Anabolic-androgenic steroid administration increases self-reported aggression in healthy males: a systematic review and meta-analysis of experimental studies

Rationale Aggression and irritability are notable psychiatric side effects of anabolic-androgenic steroid (AAS) use. However, no previous study has systematically reviewed and quantitatively synthesized effects reported by experimental studies on this topic. Objective We conducted a systematic review and meta-analysis of randomized controlled trials (RCTs) investigating the effect of AAS administration on self-reported and observer-reported aggression. Methods Twelve RCTs comprising a total of 562 healthy males were identified through systematic searches of MEDLINE, PsycInfo, ISI Web of Science, ProQuest, Google Scholar, and the Cochrane Library. Results After excluding one outlier, AAS administration was associated with an increase in self-reported aggression under a random-effects model, albeit small (Hedges’ g = 0.171, 95% CI: 0.029–0.312, k = 11, p = .018), and when restricting the analysis to the effect of acute AAS administration on self-reported aggression under a fixed-effect model (g = 0.291, 95% CI: 0.014–0.524, p = .014). However, the above effects were neither replicated in the analysis of observer-reported aggression nor after restricting the analysis to the effects of the administration of higher (over 500 mg) and long-term (3 days to 14 weeks) doses. Conclusions The present meta-analysis provides evidence of an increase, although small, in self-reported aggression in healthy males following AAS administration in RCTs. Ecologically rational RCTs are warranted to better explore the effect of AAS administration on aggression in humans. Supplementary Information The online version contains supplementary material available at 10.1007/s00213-021-05818-7.


Introduction
Anabolic-androgenic steroids (AAS) are a family of hormones comprising the androgen hormone testosterone as well as its synthetic derivatives (Kanayama and Pope 2018). Use of AAS was historically associated with weightlifters and later with professional bodybuilders and elite athletes in various sports. Since the 1980s, use of AAS has gradually spread to recreational athletes as well as the general population (Pope and Kanayama 2012). Use of AAS normally comprises long-term administration of supraphysiological doses often 10-100 times the natural production or therapeutic doses of androgens (Kanayama et al. 2013). A metaanalysis on the global prevalence of AAS use indicated that 3.3% of the world's population has used AAS at least once with use being more frequent among males (6.4%) compared to (1.6%) females (Sagoe et al. 2014b;Sagoe and Pallesen 2018).
Despite benefits such as increased muscle growth, improved body image, and enhanced sports performance (Evans 2004;Sagoe et al. 2014a;Smit et al. 2020a), human case studies, surveys, and experimental studies suggest that AAS induce a plethora of physical and psychological adverse side effects. Cardiovascular disorders, particularly cardiomyopathy, are major physical side effects of AAS use (Baggish et al. 2017). Other somatic side effects of AAS include hypertension, sleep abnormalities, immunological dysregulation, decreased libido in males, and hirsutism and clitoromegaly in females (Bensoussan and Anderson 2019;Ganesan et al. 2020). Notable psychological side effects comprise manic and depressive symptoms as well as psychotic symptoms (Brower 2009;Kanayama et al. 2020). Human case studies, surveys, and experimental studies further suggest that AAS induce a plethora of symptoms such as irritability and unprovoked aggression sometimes referred to as "roid rage" or "steroid rage" (Nelson 1989;Pope and Katz 1987;Taylor 1987;Tragger 1988). Experimental animal studies show consistently that injections of AAS increase aggression (Clark and Henderson 2003;Lumia et al. 1994). For human studies, cross-sectional (Ganson and Cadet 2019;Pereira et al. 2019), case-control (Klötz et al. 2007;Lundholm et al. 2010;Thiblin et al. 2015), and longitudinal (Beaver et al. 2008) researches indicate a positive relationship between AAS use and aggression. However, results from human placebo-controlled randomized studies show an inconsistent association between AAS administration and aggression comprising negative (Björkqvist et al. 1994), positive (Panagiotidis et al. 2017;Wagels et al. 2018), and nonsignificant findings (Tricker et al. 1996).
Most previous reviews on this topic are merely narrative (Haug et al. 2004;Huo et al. 2016;Johnson et al. 2013). Additionally, a recent review (Geniole et al. 2020) on this topic lacks some studies (Anderson et al. 1992;Björkqvist et al. 1994;Su et al. 1993;Tricker et al. 1996). Hence, a comprehensive systematic review quantifying findings on the topic is overdue in line with the merit of meta-analyses in science and evidence-based medicine (Murad et al. 2016). Against this backdrop, we conducted a systematic review and meta-analysis of randomized controlled trials (RCTs) examining the effect of AAS administration on self-reported as well as observer-reported aggression in healthy males.

Literature search strategy
Systematic literature searches were conducted in MEDLINE, PsycInfo, ISI Web of Science, ProQuest, Google Scholar, and Cochrane Library. There was no time constraint for the search. Keywords for AAS were combined with keywords for aggression. An overview of the keywords and search strategy can be found in Appendix A in the Supplementary information. The latest systematic literature search was conducted on 31 December 2019 followed by additional ad hoc searches to ensure comprehensiveness. The search and selection process are presented in Fig. 1.

Inclusion criteria and data extraction
Included studies were as follows: (1) RCTs, (2) investigating the effects of AAS administration on aggression in healthy persons, (3) based on valid aggression measures, and (4) published in English. The first author (RC) independently conducted the search and selection of articles based on the aforementioned criteria. Using a standardized data extraction form, the first and last (RC and DS) authors independently extracted the following data from the identified studies: study authors, country, design (e.g., double-blind), sample type (e.g., healthy males), sample size, age (range, M ± SD), study groups (e.g., placebo group), AAS type, AAS dose, AAS administration mode (e.g., injection), study duration, assessment type (e.g., self-report), aggression measure, results, and risk of bias (see Table 1). Furthermore, the testosterone levels both at baseline and post-administration for each study are shown in Table 2. The two authors reached consensus in cases of discrepant extractions through discussions, with the involvement of the second author SP) when necessary. We also contacted corresponding authors or, when unavailable, coauthors via email for missing information.

Statistical analysis
We first investigated the overall effect of AAS administration on self-reported aggression using a random-effects model. AAS users typically administer supraphysiologic doses of AAS for 4 to 28 weeks (Kanayama et al. 2013;Copeland et al. 2000). We therefore subsequently pooled studies in which higher doses (over 500 mg) of AAS were administered for the examination of the effect of high-dose AAS administration on self-reported aggression (O'Connor et al. 2004;Pope et al. 2000;Su et al. 1993;Tricker et al. 1996;Yates et al. 1999). Furthermore, we pooled studies in which AAS were administered over longer periods (i.e., 3 days to 14 weeks: Anderson et al. 1992;Cueva et al. 2017;O'Connor et al. 2002;O'Connor et al. 2004;Pope et al. 2000;Su et al. 1993;Yates et al. 1999) as well as studies investigating acute AAS effects (Carré et al. 2017;Dreher et al. 2016;Panagiotidis et al. 2017;Tricker et al. 1996). Due to the low number of studies administering higher doses (k = 5) or investigating acute AAS effects (k = 4), a fixed-effect model was used for these analyses (Borenstein 2009). Moreover, we conducted a meta-regression analysis to elucidate a potential dose-response association, regressing AAS dose (mg) on self-reported aggression. Finally, we investigated the overall effect of AAS administration on observerreported aggression using a fixed-effect model due to the low number of studies (k = 3: O' Connor et al. 2004;Tricker et al. 1996;Yates et al. 1999).
Some studies used multiple aggression measures and reported multiple aggression scores (O'Connor et al. 2002(O'Connor et al. , 2004Panagiotidis et al. 2017;Pope et al. 2000;Su et al. 1993). In these cases, we set the correlation between aggression measures to 0.60 (Diamond and Magaletta 2006;O'Connor et al. 2001) to provide the best estimates of between-study variance and corresponding confidence intervals (Gleser and Olkin 2009;Marín-Martínez and Sánchez-Meca 1999). For crossover studies (O'Connor et al. 2004;Pope et al. 2000;Su et al. 1993;Yates et al. 1999), we used an average correlation of 0.50 between aggression measures over time to provide optimal effect size estimates (Krahé and Möller 2010). Effects were estimated as Hedges' g, where 0.20 is considered small, 0.50 moderate, and 0.80 as large effect sizes, respectively (Hedges and Olkin 2014). For studies including a passive control group (e.g., no intervention), a placebo group, and a treatment group (Björkqvist et al. 1994), data from the placebo and treatment groups were used to estimate meaningful relative-effect estimates (Karlsson and Bergmark 2015;Magill and Longabaugh 2013). Effect sizes were calculated by pooling post-intervention mean and standard deviations of aggression scores. When mean and standard deviation were not reported or unavailable in the original paper, authors were approached by email (Björkqvist et al. 1994), and asked to provide statistical information (i.e., F and p values) necessary to calculate effect sizes. For the assessment of heterogeneity, we used the Q-statistic and the I 2 index. The latter indicates the proportion of the observed variance that reflects real differences in effect size. It is expressed as a percentage (0-100) with 0% indicating no heterogeneity,  25% indicating low heterogeneity, 50% indicating moderate heterogeneity, and 75% suggesting high heterogeneity (Higgins et al. 2003) respectively. Additionally, we used Duval and Tweedie's (2000) trim and fill method, and Orwin's (1983) fail-safe N to assess publication bias. The trim and fill method (Duval and Tweedie 2000) screens for missing studies and adjusts the effect size by trimming the asymmetric studies and filling a funnel plot symmetrically. Orwin's (1983) fail-safe N quantifies the number of studies required to bring the observed effect size down to a chosen "trivial" estimate (Hedges and Olkin 2014). In the current meta-analysis, we set the "trivial" estimate to g of 0.05. The quality of each included study was assessed using the Cochrane risk of bias tool (Higgins et al. 2003). The protocol for the meta-analysis was pre-registered in PROSPERO (CRD 42019117834). The literature search, coding of variables, and reporting were conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) procedure (Moher et al. 2009). The meta-analysis and the meta-regression were performed using the Comprehensive Meta-Analysis version 3.3.070 (Borenstein et al. 2014).

Literature screening and selection
From an initial pool of 30,407 hits, 18,988 records remained after removal of duplicates (k = 3772) and gray literature (k = 7649) during initial identification and screening. Of this pool, 18,752 were removed after eligibility screening by title and abstract leaving 238 records for further evaluation. After screening the 238 full-text records, 12 studies were finally included. Figure 1 presents the literature search and selection process.
Testosterone enanthate was administered in four studies (Anderson et al. 1992;Dreher et al. 2016;O'Connor et al. 2002;Tricker et al. 1996) and two studies administered testosterone cypionate (Pope et al. 2000;Yates et al. 1999). In addition, two studies administered testosterone undecanoate (Björkqvist et al. 1994;O'Connor et al. 2004), and three studies administered testosterone gel (Carré et al. 2017;Cueva et al. 2017;Panagiotidis et al. 2017) whereas one study administered methyltestosterone (Su et al. 1993). AAS doses ranged from a one-time application of 50 mg of testosterone gel (Panagiotidis et al. 2017) to a one-time injection of 1000 mg of testosterone undecanoate (O'Connor et al. 2004), and a cumulative injection of 7000 mg of testosterone cypionate over a 14-week period (Yates et al. 1999). When various doses of AAS were used in one study, we used results from the highest dose for calculating the effect size.

Risk of bias
The two authors disagreed once on the random sequence generation dimension for all the included studies yielding a Cohen's kappa of .58 (Cohen 1988). All studies were evaluated as having a high selection bias as there was no description of the randomization method or concealed allocation process.
In addition, all studies were evaluated as having high risks of performance and detection bias as the effectiveness of blinding was not tested. Moreover, all studies had a low risk of attrition bias as there was sufficient reporting and handling of attrition and exclusion. Furthermore, except for one study that did not present means and standard deviations or inferential indices (Björkqvist et al. 1994), we evaluated all studies as having low reporting bias. Figure 2 depicts the risk of bias of the included studies.

Effect of AAS administration on self-reported aggression
Of the twelve included studies, one study (Björkqvist et al. 1994) did not overlap with the 95% CI of the overall pooled effect size. Exclusion of this outlier resulted in a mean and significant random-effects size of g = 0.171 (95% CI: 0.029-0.312, k = 11, p = .018), and there was no significant heterogeneity between the included studies (I 2 = 0.000, Q = 8.891, p = .542). The effect sizes and associated 95% confidence intervals are presented in Fig. 3. The overall random-effects of AAS administration on selfreported aggression, including the outlier (Björkqvist et al. 1994), was not significant (g = 0.081, 95% CI:

Effect of long-term AAS administration on self-reported aggression
The random-effects of administering AAS over longer periods (3 days to 14 weeks) on self-reported aggression under a random-effects model was g = 0.100 (95% CI:−0.079-0.278, p = .273). There was no significant heterogeneity across studies in terms of effect sizes (I 2 = 5.286, Q = 6.335, p = .321). (See Fig. 4.)

Effect of AAS administration on observer-reported aggression
The overall fixed-effect of AAS administration on aggression based on observer ratings resulted in an effect size of g = 0.157 (95% CI: −0.026-0.581, p = .469, Q = .249, p = .833). The effect sizes and associated 95% confidence intervals for each study are presented in Fig. 7.

Discussion
The present systematic review and meta-analysis of eleven studies (Anderson et al. 1992;Carré et al. 2017;Cueva et al. 2017;Dreher et al. 2016;O'Connor et al. 2002O'Connor et al. , 2004Panagiotidis et al. 2017;Pope et al. 2000;Su et al. 1993;Tricker et al. 1996;Yates et al. 1999), after excluding an outlier (Björkqvist et al. 1994), indicates that AAS administration is associated with an increase in self-reported aggression, albeit small, among healthy males in RCTs. This finding is consistent with the results of a recent meta-analysis (Geniole et al. 2020) indicating that testosterone administration has a small and positive correlation with aggression in males. Relatedly, our finding that acute AAS administration has a positive effect on self-reported aggression is consistent with evidence that acute increases in testosterone have a positive correlation with aggression (Geniole et al. 2020).
The present study is the first comprehensive systematic review and meta-analytic investigation of the effect of AAS administration and aggression in healthy males in RCTs. However, our results should be interpreted with caution. Firstly, a meta-regression examining dosage as a moderator of the identified effect of AAS on self-reported aggression turned out not significant. Similarly, we did neither detect an effect of AAS administration on observer-reported aggression nor for the effects of long-term (3 days to 14 weeks) and highdose AAS administration on self-reported aggression. Also, as noted previously, only healthy males were examined in the included RCTs and the duration and doses used in the twelve RCTs deviate from the prolonged use of high-dose cycles consisting of the ingestion of supraphysiologic doses of different types of AAS per week over several months (Kanayama Study Fig. 4 The effect (random-effects model) of administering AAS over longer periods on self-reported aggression et al. 2013) often reported by users in ecologically valid settings. In one study, the reported weekly AAS dose ranged from 125 to 7000 (mean = 1278) mg per week over an average of 9.1 years (Bjørnebekk et al. 2017). In another recent study, it was shown that an AAS cycle usually comprises the ingestion of five different AAS with an average dose of 901 mg per week for a typical duration of 13 weeks (Smit et al. 2020b). In the present meta-analysis, the highest dose administered was a one-time injection of 1000 mg of testosterone undecanoate (O'Connor et al. 2004) and a cumulative injection of 7000 mg of testosterone cypionate over a 14-week period (Yates et al. 1999). Inferably, AAS doses and duration of administration in the RCTs included in our meta-analysis are far lower than the actual doses reported by AAS users (Bjørnebekk et al. 2017;Kanayama et al. 2013). Similarly, besides the administration of methyltestosterone in one study (Su et al. 1993), fluoxymesterone, oxymetholone, and trenbolone that are anecdotally associated with increased aggression in humans (Barker 1987;Llewellyn 2011) were not administered in the RCTs included in the present review. Moreover, testosterone undecanoate administered in two studies (Björkqvist et al. 1994;O'Connor et al. 2004) is a depot with a very gradual decay and long half-life leading to relatively stable testosterone levels over a prolonged period of time (Hirschhäuser et al. 1975). Hence, discrepancies in AAS doses, type, duration of use, and half-life between the AAS in the RCTs and naturalistic contexts should be noted when interpreting our findings.
In addition, evidence from cross-sectional studies indicates that polypharmacy and stacking (Sagoe et al. 2015;Salinas et al. 2019) may account for increased aggression among AAS users (Lundholm et al. 2015). The absence of polypharmacy in the RCTs included in our meta-analysis may also explain the discrepancy between findings from RCTs and those reported in more ecologically valid contexts. Other potential confounding factors include small sample sizes and lack of a priori power analyses, diversity in aggression measures, risk of bias (selection, performance, and detection biases), diversity in route of administrating AAS (injecting, transdermally), diversity in time gap between AAS administration, incomplete data reporting, and sampling of only males in included RCTs.
Moreover, the inclusion of only healthy volunteers in the RCTs may have precluded vulnerable subjects from participating which may have led to the underestimation of the effects of AAS administration on aggression. Sampling is important with evidence that testosterone increases aggression in men with certain personality profiles especially among those with fewer cytosine-adenineguanine repeats in exon 1 of the androgen receptor gene (Geniole et al. 2019). The importance of sampling is further evidenced in that, apart from bodybuilders and competitive athletes, a large portion of non-experimental research linking AAS use with aggression has been conducted among subgroups associated with aggression such as drug users, offenders, and prisoners (Lundholm et al.  Fig. 6 The effect (fixed-effect model) of administering higher (over 500 mg) doses of AAS on self-reported aggression 2010; Pope et al. 1996), as well as policemen, doormen, and nightclub bouncers (Hoberman 2017;Midgley et al. 2001). Future researchers considering the aforementioned factors may conduct more ecologically valid RCTs (e.g., by using dosages and duration of use similar to those by real AAS users) to better elucidate the effect of AAS administration on aggression in humans. Furthermore, more studies should explore factors of AAS administration (e.g., type of AAS, duration of use, premorbid functioning, and genetics) that might moderate the effects of AAS on aggression.

Conclusions
The present systematic review and meta-analysis provide evidence for an increase, although small, in self-reported aggression in healthy males following AAS administration in RCTs. Moreover, when restricting the analysis to the effects of acute AAS administration on self-reported aggression, we found a significant effect. We also identified important limitations of the RCTs on issues such as nonecological doses, lack of personality and polypharmacy controls, small sample sizes, risk of bias, short study duration, and the inclusion of only healthy males. While future RCTs adjusting for the above factors may contribute better to contemporary understanding of the effect of AAS administration on aggression in humans, the present study provides an important foundation for addressing this important public health issue. As the appreciation of the heterogeneity of AAS use matures, there is a need to identify the role that AAS plays in aggression and violence and what may be attributed to the set and setting of their use.
Funding Open access funding provided by University of Bergen (incl Haukeland University Hospital).

Declarations
Conflict of interest The authors declare no competing interests.
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