Background

According to the DSM-5, nightmares are an intrusive dream and may be idiopathic or associated with disorders such as nightmare disorder, PTSD, substance abuse, and schizophrenia [1]. As nightmares may also be a risk factor for PTSD, and can be present after the successful treatment of PTSD, some researchers suggest that nightmares should be screened, diagnosed, and treated [2]. Furthermore, the International Classification of Sleep Disorders (ICSD) recognize and describe nightmare disorder as a REM parasomnia, affecting more than five percent of the US population [3]. Nightmare disorder is related to repeated (at least once per week), well remembered nightmares that result in rapid awakening, and mood, sleep, and behavioural problems more generally [4]. PTSD related nightmares can be considered a distinct subset of nightmare disorder [5]. Researchers believe there may be a genetic component to nightmares and a strong association with neuroticism and trauma [6]. Since 2000, research has increasingly considered nightmares as a complex phenomenon with multiple presentations and a potential stand alone disorder, rather than just a symptom of sleep disorders as previously thought.

Currently, nightmare disorders are under diagnosed, and may be prevalent in as many as 5% of the population. Nightmares have also been shown to increase the risk of suicide behaviours in depressed patients [7], and are associated with increased interpersonal violence [8]. Frequent nightmares may relate to a five-fold increase in the likelihood of having a psychiatric illness [3, 9]. Nightmares are reported more commonly by women, but no sex differences occur in children or in older adults [10]. Nightmares have also been reported across multiple geographic and cultural contexts. Due to the high prevalence of nightmares in all populations and their links to psychopathology it is important that we develop and evaluate evidence-based treatments.

Studies on nightmares and nightmare treatment in children are currently limited, especially younger children, with prevalence rates estimated to be similar to adults (approximately 5%) [11]. Nightmares in children are associated with a wide range of sleep related, emotional, developmental, and behavioral problems [12]. In a sample of treatment seeking war-exposed youths, nightmares were associated with significant suffering, with the most common nightmare themes being fear (77%), grief (20%), and hopelessness (19%)  [13].

Psychosocial treatments

The results of meta-analytic reviews suggests that psychosocial treatments can reduce nightmare frequency and intensity with medium effect sizes commonly reported [14, 15]. Systematic reviews support the efficacy of trauma focused CBT, especially image rehearsal therapy (IRT), for nightmares, however there are limited high quality clinical trials [16,17,18]. The American Academy of Sleep Medicine (AASM) recommend image rehearsal therapy (IRT) for PTSD related nightmares and nightmare disorders, and also list a number of “may be used” treatments such as cognitive behavioral therapy (CBT), eye movement desensitization and reprocessing (EMDR), and exposure, relaxation, and rescripting therapy (ERRT) [19]. They also stress the importance of tailoring treatment to the specific client and context. The British Association for Psychopharmacology review of treatments recommends psychosocial interventions for nightmares that include exposure, writing down dreams, guided imagery, pleasant images, and changing the ending [20]. There are however some inconsistencies and unknowns in the current guidelines. For example, CBT is considered a first line treatment by the British Association for Psychopharmacology, but a second line treatment by AASM. There is also a lack of evidence for psychosocial treatments for severe nightmares and severe nightmare disorders. Most of the current trials are mild to moderate cases.

Rousseau and Belleville [21] systematically reviewed the mechanisms by which nightmares are treated psychosocially. They concluded that an increased sense of mastery was the most commonly cited explanation for therapeutic benefits. Reductions in arousal, fear and avoidance, improved sleep, and modification of beliefs were also cited as mechanisms of action for psychosocial interventions for nightmares.

Consistently, IRT is listed as a first line treatment. IRT involves the client writing down the dream or drawing it in the case of children. The client is then encouraged to imagine themselves acting differently. This often involves imagining an action or series of actions that replace non-action. This encourages a re-imagining where action is taken rather than flight. The client can write or draw these alterations, and are encouraged to repeat this process consistently at home  [6].

Pharmacological treatments

There is also extensive research on drug treatments for nightmares. According to Morgenthaler et al., [19] pharmacologic treatment may be slightly more effective than psychosocial treatments. They also suggest that there is conjecture over the lasting effects of these drugs once withdrawn, and that we are still unclear about the underlying pathophysiology of nightmares. There is also a need to better understand interaction effects between anti-depressants and nightmare specific drugs such as prazosin. The AASM currently suggest that the following drugs may be beneficial for treating nightmares; the atypical antipsychotics olanzapine, risperidone, and aripiprazole; clonidine; cyproheptadine; fluvoxamine; gabapentin; nabilone; phenelzine; prazosin; topiramate; trazodone; triazolam; nitazepam; and tricyclic antidepressants. One of the most widely studied, reviewed and utilized treatment drugs for nightmares is the alpha-1 adrenergic blocker prazosin [22]. The British Association for Psychopharmacology review of treatments stated that there was good evidence for the use of prazosin for reducing nightmares in adult and pediatric populations [20]. However, while still supporting its use, the AASM downgraded the effectiveness of prazosin for nightmares in 2018.

Suraev et al [23] and Betthauser et al [24] systematically reviewed cannabinoid therapies for managing sleep disorders and despite some promising preliminary evidence, both studies suggested that there is currently an absence of high quality clinical trials to support its use. Cowling and MacDougall [25] reported that the synthetic cannabinoid nabilone could reduce PTSD related nightmares. Dagan and Yager [26] argued that while medical cannabis could reduce nightmares, it may have negative effects on other PTSD symptoms such as dissociation and reckless behaviours. There is also some evidence for the use of anti-depressants in treating nightmares. A systematic review of the links between dreaming and anti-depressants found differing effects depending on the type of anti-depressant taken, including withdrawal effects, and concluded that more research is needed to draw conclusions [27]. In addition, side effects of some anti-depressents include an increase in nightmares. In summary, there is limited evidence supporting the use of cannabis or anti-depressants for nightmares. However, as an emerging area of investigation, an up to date review of research findings is needed.

In summary, treatment for nightmares and nightmare disorder include psychotherapeutic treatments such as image rehearsal therapy, pharmacological interventions such as prazosin and nitrazepam that affect the neurotransmitters, and atypical antipsychotics such as olanzapine. In recent times there have been numerous studies that have evaluated the effectiveness of treatments for nightmares, resulting in some changes to understanding of best practice. For example, some psychosocial treatments recently trialed include eye movement desensitization and reprocessing, and sleep dynamic therapy. In 2018, the AASM released a position paper (rather than a clinical practice guide) due to the limited number of high quality studies providing direct evidence of treatments for nightmares [19]. In addition, many studies in this area have evaluated treatments for sleep related outcomes in general, rather than treatments for nightmares specifically. There is also a lack of a universal outcome measure for nightmares which makes comparing study results difficult. As such there is a need to systematically review findings related to the effectiveness of treatment of nightmares to inform best practice. This current study reviewed psychosocial treatments for nightmares and adds to the review literature by including non-RCTs, studies on children, and a focus on newer (for nightmares) psychosocial treatments. We aimed to answer the following questions:

What is the effectiveness of psychosocial treatments for nightmares in adults and children?

What are the new promising psychosocial nightmare treatments for adults and/ or children requiring further investigation?

Method

This report followed the systematic review reporting guidelines suggested by Moher et al. [28] A review protocol was registered with PROSPERO (CRD42020204861). This paper reported the psychosocial findings from this protocol.

Searching the literature

An initial search was conducted to find current meta-analytic, systematic review, and review articles using SCOPUS (2000-Present), PsychINFO (2000-Present), and MEDLINE (2000- Present) databases and the search terms “nightmare AND review OR analysis”. This informed the focus of the current review and the information presented in the introduction section of this report. A search was performed to collect relevant studies for the systematic review. The databases SCOPUS, PsychINFO, CINAHL, and MEDLINE were searched using the search terms “nightmare AND therapy OR treatment OR intervention”. Relevant database subject heading search terms were also included. In addition, the Cochrane data base was searched for trials (n = 582) and reviews (n = 65) using the search term “nightmare”.

Reference lists of more recent studies were screened for studies not picked up by the search. The final search was performed on August 30, 2020.

The following inclusion criteria was used to screen studies:

  1. 1.

    Available in English or English translation.

  2. 2.

    Published in 2000 or later. Prior to 2000, research more commonly considered nightmares as a symptom of sleep disorders more broadly rather than a stand-alone disorder.

  3. 3.

    Reported findings related to the effectiveness of psychosocial or pharmacological treatments.

  4. 4.

    Included any nightmare symptoms reported as an outcome variable, either as a specific focus of the study such as in nightmare disorder, or as part of a broader outcome evaluation such as sleep disturbance or PTSD.

  5. 5.

    A peer reviewed scientific journal article.

Excluded from the review were review articles, theoretical or commentary articles, books, audio documents, posters, symposiums, and classification manuals. For this manuscript, only studies evaluating psychosocial treatments were presented.

Study selection and data extraction

The first author reviewed all eligible studies. Studies were screened at two stages, title and abstract, and full text. Eligibility assessment was performed independently in a blind standardized manner by two reviewers for title and abstract, and one reviewer for full text using the software COVIDENCE. Overall agreement rates were 84.5%, for title and abstract screening with discrepancies solved through discussion in regular meetings between the two reviewers.

Data were extracted by two reviewers, and included the following:

  1. 1.

    Study, authors, date, and country

  2. 2.

    Sample characteristics (age, sex, military or civilian, nightmare severity/ presentation)

  3. 3.

    Study design/ protocol (experimental, RCT, trial, case series, pilot)

  4. 4.

    Outcome measures; nightmare frequency (number of nightmares, number of nights with nightmares), nightmare severity (intensity, distress caused)

  5. 5.

    Treatment type/ format/ length/ duration

  6. 6.

    Attrition rate/percentage

  7. 7.

    Outcomes (effects within and between groups, including follow up)

  8. 8.

    Study limitations

Risk of bias within studies

A process for assessing bias within RCT studies was formulated according to Cochrane recommendations [29] and using the COVIDENCE software template. For RCTs an assessment for each study was made and reported as either low risk, high risk or unclear risk;

  1. 1.

    Selection, allocation, group differences at baseline

  2. 2.

    Blinding of participants, personnel, and outcome assessment, non-planned treatment differences

  3. 3.

    Differences in how group outcomes were assessed, non-validated measures of nightmares

  4. 4.

    Incomplete outcome data, Attrition differences between groups

  5. 5.

    Selective Outcome Reporting

For non-RCTs, several tools were considered including the Risk of Bias in Non-Randomized Studies—of Interventions (ROBINS-I) [30], and the Joanna Briggs Institute (JBI) critical appraisal checklist for case reports [31]. However, due to the variability of study designs included, a selection of relevant criteria were assessed for each study and reported as either low risk, high risk, or unclear risk. These assessments were made based on a comparison to the other non-RCTs in this collection rather than in comparison to the stringent RCT expectations.

  1. 1.

    Participant selection – minimum frequency of nightmares stated or met (once per week)

  2. 2.

    Confounding variables – concurrent psychological or pharmacological treatment

  3. 3.

    Blinding of outcome assessors

  4. 4.

    Selective Outcome Reporting

  5. 5.

    Data Sampling

The percentage of published articles with significant findings were also considered along with collective estimates of conflicts of interest and funding sources.

Data synthesis

Data synthesis was performed narratively. Due to the diverse outcome measures, treatments, and samples evident in the literature on nightmares, a focused narrative approach allowed for the best synthesis of the data. Studies were grouped into main categories in relation to the type of treatment, including group or individual, type of psychosocial treatment, and also by age, adults and children. Further sub-categories were devised for grouping treatment types; CBT based, Exposure based, Image rehearsal/rescripting based. Once all articles were grouped into categories, the collective efficacy was assessed. This process was completed in discussions between two of the researchers and resulted in therapies being classified at low, medium, or high on quantity of evidence, quality of evidence, and support for use. This process was informed by the effects reported and the risk of bias. A conclusion was generated for all groups and sub-groups and then reported.

Changes to PROSPERO

The primary change to this study was in study selection. Full text reviewing was conducted by one reviewer rather than two reviewers. This occurred due to the withdrawal of one of the reviewers from the research. It was decided to proceed with the primary reviewer alone rather than include a new reviewer who was less familiar with the studies. Due to the large number of studies included, the decision was made to report the study in two separate papers (psychosocial and pharmacological). We acknowledge that comparisons between the two broad treatment modalities are important, and will be discussed in a subsequent manuscript.

Results

Description of selected studies

The strategy for literature search and selection is outlined in Fig. 1. Title and abstract review resulted in 454 eligible studies. After excluding 389 studies for the reasons listed in Fig. 1, there remained 65 studies for the qualitative synthesis. The 35 RCT studies comprised a combined 3048 participants (F = 1940, M = 1108), with mean ages ranging from 10 to 59 years. The 34 non-RCT studies comprised a combined 500 participants (F = 170, M = 327, Transgender = 3) with ages ranging from 4 to 71 years. Only two RCTs and 7 non-RCTs included children and/or adolescents. Most RCT studies originated from either the USA (N=19) or the Netherlands (N=7), and 12 of the studies had military or military veteran samples. For the non-RCT studies, most studies originated from the USA (N = 27) and had civilians with PTSD (N = 11) or military or military veteran sample with PTSD (N = 13). Participants were most commonly suffering from PTSD (N = approximately 1880) or idiopathic (N = approximately 450) nightmares. Female participants were commonly victims of sexual assault, while males commonly suffered from war related trauma. The most common therapies evaluated were image rehearsal/rescripting-based therapies (N= 34), exposure-based therapies (N= 8), mixed exposure and image rehearsal based therapies (N=11), and CBT based therapies (N=6). The interventions consisted of individual, group, and self- help/directed modalities, ranging from 1 to 20 sessions in total, with each session lasting between 60 and 180 minutes. Attrition rates for the 35 RCT studies ranged from zero to 46% from baseline to final measurement. For the non-RCT studies, attrition rates ranged from zero to 64.7%. Most studies included follow up measurement/s of between 4 weeks and 12 months. The nightmare related outcomes measured included frequency (total number, number of nights with), intensity, and related distress, measured by self-report or a standardized instrument. The majority of RCT studies assessed both within and between group effects using analysis of variance, whereas most of the non-RCTs did not use a comparison group, assessing within-subjects effects only.

Fig. 1
figure 1

PRISMA Flowchart of Literature Search and Selection

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RCTs

One study (see Table 1) assessed the efficacy of treatment for children [32] and found that a self-help form of IRT significantly reduced nightmare frequency compared to a passive control (sustained at 9 month follow up). Another study assessed IRT with an adolescent (13 years to 18 years) female only cohort and found significant reductions in nights and nightmares per month compared to no significant changes in the control group [33].

Table 1 Summary of RCTs examining psychosocial treatments of nightmares
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Of the remaining studies that assessed forms of image rehearsal or rescripting therapies, all but one showed significant reductions in nightmare symptomatology. All of the exposure and exposure plus image rehearsal studies found significant symptom reduction. While the CBT and CBT-I interventions were found to be effective, two of the five studies found exposure or IRT treatments to be superior. The two studies of cognitive processing therapy (CPT) showed significant symptom reduction, while the two studies of lucid dreaming therapy (LDT) showed inferior results to exposure therapy. Psychosocial therapies outperformed passive controls in most studies and were at least equivalent to pharmacological interventions. Group and individual therapies were shown to be equally effective across a range of treatment types, and all but one self-guided therapy study produced significant symptom reduction. Treatment effects were sustained or increased at follow-up in most studies. Effects appeared independent of the sample presentation (idiopathic or part of a more complex presentation).

Risk of bias (RCTs)

As shown in Table 2, all studies randomly assigned participants to treatment groups, although nearly half of the studies failed to report the randomization technique in sufficient detail for replication. The majority of studies blinded participants, however, several studies reported problems with the blinding process, which may have resulted in participants being aware of their group allocation. All studies were single blinded based on the difficulty of blinding clinicians to the treatment they deliver. There was little evidence of incomplete outcome data and selective reporting, and the majority of studies blinded the outcome assessment. It was noted that many studies failed to report between group effects in the abstract and in concluding, reporting just the within group changes. In a minority of studies, this gave a false impression that reported effects were based on comparisons to the control group. A minority of studies failed to report attrition rates.

Table 2 Risk of bias of RCTs examining psychosocial treatments of nightmares
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Non-RCTs

The studies reviewed (see Table 3) included 7 case studies, 10 case series, and 16 before and after studies, of which one utilised a control group for part of the study [68]. The case studies were mostly medium (5 – 10 sessions) to long (15+ sessions) in length of treatment, whilst the case series were mostly brief (1- 2 sessions) or short (3 - 4 sessions). The before and after studies included a mixture of different lengths. Effectiveness comparisons by length of treatment did not reveal notable findings. All 34 studies reported an improvement in one or more nightmare symptom, with half of these studies conducting analyses of significance.

Table 3 Summary of Non-RCTs examining psychosocial treatments of nightmares
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The image rehearsal or rescripting therapies were the most common form of intervention used. Half of these rescripting studies also included CBT-I or select features (e.g., stimulus control, sleep restriction, and/or sleep hygiene) in their treatment delivery. Significant reductions in various nightmare symptomatology were reported in half of the rescripting studies. Six of the remaining studies reported decreases in symptomology however did not conduct analyses of significance. One of these also reported a slight increase in mean frequency of nightmares whilst observing decreases in nightmare distress, intensity, and vividness [69]. The final study found non-significant improvements, however measured dreams rather than nightmares specifically [81]. The only study delivering CBT-I alone provided weak positive results  [79].

Two of the six studies employing mixed exposure and image rehearsal-based therapies through ERRT reported significant improvements in nightmare symptomology. The remaining four studies reported improvements, without measuring statistical significance. Kovacevic and Davis [86] used CPT following ERRT and found nightmare frequency and severity reduced following ERRT and then further decreased until cessation during CPT. Of the two exposure-only studies, the self-directed study found that significant reductions were maintained over 4 years of follow-ups [82] and the other study reported an extinction of nightmares maintained at 1 and 3month follow-ups but did not conduct analyses of significance [72].

The two EMDR studies [98, 101] reported improvements in nightmare symptomology, however, both were third person accounts (mother and doctor), with no formal statistics or analyses. The two hypnotherapy studies reported improvements, however neither used analyses of significance. Furthermore, Hauri et al [85] post assessment did not separate nightmares participants from the other parasomnia participants. The embodied imagination case report [100] declared an extinction of nightmares however did not use statistics or follow up. The lucid dreaming therapy study reported a decrease in mean nightmare frequency, however, the number of participants who were successful in lucidly changing their dreams was the same as the number of participants whose dreams changed without lucidity.

Seven of the 34 studies explored treatments (3 IRT, 1 ERRT, 2 hypnotherapy, and 1 EMDR) in adolescents and children (aged 4 – 16 years). Nightmare symptoms improved in each study, however, Davis et al [75] and Fernandez et al [78] noted the need to rewrite the child’s script before improvements occurred. Interestingly, this coincided with the end of therapy; which meant no further therapist driven exposure work. Also noteworthy was that Hauri et al [85] used a mixed sample of children and adults and did not comment on child outcomes specifically.

Regarding sample presentations, three studies clearly stated the use of civilians with idiopathic nightmares, nine studies included posttraumatic civilian cohorts, and 12 studies included posttraumatic military cohorts. The remaining nine studies consisted of cohorts which were either mixed (idiopathic and posttraumatic), unclear (did not state civilian/military and/or idiopathic/posttraumatic), or complex (e.g., psychiatric) in their presentations. There was a mixture of therapies amongst the different cohorts however, the posttraumatic cohorts (civilian and military) mostly received IRT with CBT-I or its sleep features.

In comparing individual delivery (n = 22) with group delivery modes (group = 5, mixed group and individual = 3, and mixed parent-child dyad = 3), the group delivery made up the majority of reported significant improvements in nightmare symptomatology. Many of the individual delivery studies reported improvements but either did not conduct analyses (e.g., all the case reports) or did not report formal statistics.

Finally, many studies collected formal follow up data (n = 16), whilst others used informal follow up through third parties (e.g., doctor/parent report; n = 2). In most of these studies, treatment gains were sustained or increased. This left 15 studies that did not employ any follow up.

Risk of bias (non-RCTs)

As shown in Table 4, the majority of studies included participants with the common baseline frequency of nightmares of at least one per week. Those rated as high either used vague terms such as “frequent” or “recurrent” to describe baseline nightmare frequency or included participants with less than 1 nightmare per week, or without nightmares at all. Most studies did not comment on whether participants were receiving concurrent psychological or pharmacological support or only addressed one of these elements. Most studies did not explicitly report on blinding of outcome assessors, or reported that the outcome assessor was also involved in the delivery of the treatment and the in-session assessments. No other blinding was reported. Regarding selective outcome reporting, studies were mixed in their attention to reporting on all outcomes and dropouts. Finally, in considering data sampling in the context of this group of non-RCTs, there was a mixed response. Data collection and reporting methods were considered, with several studies failing to use formal statistics or collection methods. The frequency of data collection (e.g., daily/each session/follow-up), and sample size were considered as part of risk.

Table 4 Risk of bias of non-rcts examining psychosocial treatments of nightmares
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Discussion

This review examined the effectiveness of psychosocial treatments for nightmares. In line with evidence hierarchies [102] and the author’s risk of bias assessments, conclusions drawn around efficacy prioritised information gathered from the RCTs over the non-RCTs. Results demonstrated that image rehearsal and rescripting based therapies had the highest quantity of evidence and strong support for their effectiveness in adults (Table 5). Symptom reductions were generally held or improved at follow up. Similarly, there was strong support for the use of exposure-based therapies and ERRT. There was moderate support for the use of CBT based therapies, while the use of LDT, hypnotherapies, and EMDR require more evidence.

Table 5 Summary of psychosocial treatment efficacy for nightmares
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While most studies reported changes in symptomology with medium to large effect sizes, very few studies reported high remission rates. These findings are consistent with current guidelines where IRT is a recommended treatment along with other “may be used” treatments [19, 20]. It appears that rehearsal and exposure-based therapies specifically target the nightmare content, reducing the emotional arousal associated with the nightmare and/or modifying the content of the nightmare [6]. Harb et al [103] described the core aspects of IRT, as commonly reported in intervention studies, as “choosing a target nightmare, rescripting it, and rehearsing a new dream” (p. 571). This supports Rousseau and Belleville’s [21] review findings where the client’s increased sense of mastery was the mechanism of change in reducing nightmare frequency and intensity. As such, techniques that promote control over the dream content or responses to dream content appear to be most effective for treating nightmares.

There was insufficient evidence to warrant recommendations for promising new (in relation to nightmares) treatments such as CPT and EMDR, however, these treatments would benefit from further high-quality research. Both RCTs assessing CPT [43, 52] reported significant decreases in nightmare symptomology, and the non-RCT study investigating CPT reported an extinction of nightmares [86]. Unfortunately, there were no RCTs of EMDR within the timeframe searched for this review to be able to reevaluate Morgenthaler et al.’s [19] label of EMDR as a treatment to only be “considered”. However, the two non-RCT EMDR studies [98, 101] reported an extinction of nightmares. Hence, RCTs are required to confirm the effectiveness of EMDR.

Findings of the current review suggest that psychosocial treatments have the potential to be beneficial across varied lengths or modes, and for both idiopathic and PTSD nightmares, however further trials and meta-analyses are required. Treatment effects were consistent across gender and age. However, as most studies were US based, research would benefit from investigation of other cultural groups. Treatments as short as two sessions and self-guided treatments produced significant benefits [48, 49, 51]. This suggests that image rehearsal and exposure techniques might be used as part of broader treatment plans for complex presentations such as PTSD. They may be introduced early in treatment to produce relatively quick symptom relief, helping to facilitate subsequent treatment benefits. For this early introduction to be employed with children, and further investigated in RCTs, the appropriateness of the script is important [75, 78]. This includes ensuring that children believe their script, and are not too afraid of the script for its resemblance to the nightmare. After discovering these issues, two non-RCTs reported on the need to rewrite the children’s scripts before observing positive gains [75, 78]. It must also be noted that exposure therapies were found to be effective when delivery was spaced at once or twice a week over 8 weeks, but not effective when delivered once a day for two weeks [61]. Due to the observed flexibility in delivering exposure and image rehearsal techniques in brief, group, and self-guided modes, these modes and techniques may provide clinicians and clients an affordable, efficient, and effective means of reducing nightmare symptoms. More high-quality research on brief and self-guided therapies is needed to support these claims.

One of the difficulties in reviewing studies for the current review was the broad range of often overlapping treatments. For example, IR, IRT, RTM and LDT all involve reimagining the nightmare but differ in other treatment protocols. Similarly, the authors chose to group different but related exposure-based treatment protocols. Furthermore, the non-RCTs demonstrated that protocols within therapies can differ (e.g., IRT or ERRT), with many studies reporting modifications such as removing exposure components [86, 96], lengthening or adding sessions or interventions (i.e., mindfulness) [69], or sometimes drawing instead of writing the dream in the case of children [68]. Similarly, Harb et al’s [103] review of IRT studies found fundamental differences in study quality and protocols. Currently, there is insufficient evidence to explore the nuanced differences in the treatment effectiveness of more specific treatment protocols. Most RCT studies in this review reported that a proportion of participants were using pharmacological treatments for nightmares at baseline, making interaction effects a confounding variable. Due to the high prevalence of nightmares in children, there is an urgent need for RCTs that examine treatment effectiveness in this cohort. The non-RCT child studies demonstrated a variety of data collection methods. It is recommended that future researchers take into account the underestimation effect of parent report and the potential for exaggeration of child self-report by using immediate and frequent reporting. Moreover, it is difficult to determine whether younger children can accurate self-report the difference between distressing dreams and nightmares that awaken the dreamer [104].

It was also noted that some of the studies reviewed made unwarranted conclusions based on within group effects and were potentially misleading. It is therefore recommended that comparison effects between treatments and controls be clearly stated in the abstract. In contrast to a recent review [21], and despite the numerous instruments used to measure nightmare symptoms, measurement of outcomes was not found to be a limitation in evaluating studies. However, there were some non-RCT studies that did not report formal statistics and instead used descriptors such as “recurrent” to “stopped” when explaining nightmare frequency [100]. Overall, most research measured some combination of frequency, intensity, and distress, making comparisons possible. Adverse events were also not recorded or reported in many studies.

There were also limitations associated with the current review. Firstly, due to research team changes, full text inclusion review was conducted by one researcher at a time. As meta-analytic synthesis techniques were not used, combined treatment effects cannot be specified. Additionally, the search strategy was limited to four databases and a specific timeframe which resulted in the most recent research not being included. Risk of bias across studies was not assessed. Finally, we did not specifically synthesize treatment effectiveness for idiopathic and PTSD related nightmares separately. While they did appear to overlap in terms of effective treatments, this may represent limitations in the studies reviewed and in the current synthesis of data. The data tends to homogenize and understate the range of nightmare presentations.

In conclusion, this study systematically reviewed nightmare treatments from 2000-2020. Thirty-five RCTs and 34 non-RCTs were included and provide strong evidence for the efficacy of exposure and image rehearsal-based treatments. These treatments reduced nightmare frequency, severity, and distress, in civilian, military, idiopathic, and PTSD cohorts. There is emerging evidence that self- guided and brief treatment modalities offer efficient and effective treatment options, however more high-quality research is needed. Additionally, there is an urgent need for clinical trials on treatment effectiveness in children. Overall, the results suggest that treatments are most effective when they facilitate a sense of control or mastery by directly targeting the nightmare content and/or the client’s emotional responses to nightmare content.