Introduction

Cannabis use for medicinal purposes has become popular in recent years, especially for symptom or treatment effects management among people living with cancer (PLWC) [1]. Prior research studies have well-documented the use of cannabis for the management of various symptoms including nausea, vomiting, and inducing sleep and appetite in PLWC [2, 3]. With the current trend of cannabis legalization and normalization in the United States (US) and overseas, its use is increasing rapidly among the general population [4]. In the US, medical cannabis (MC) is now legally permitted in 38 states, four US territories, and the federal District of Columbia (D.C.). Furthermore, non-medical use of cannabis has been legalized in 23 states, three US territories, and D.C. [5, 6]. The prevalence of cannabis consumption is notably higher in North America, as well as affluent European and Oceania nations, in comparison to low and middle-income countries where there has been a smaller but rising trend in cannabis use [7]. Despite varying cultural practices, cancer is an internationally accepted medical condition that qualifies for the clinical application of cannabis; PLWC frequently use cannabis as a means of symptom and treatment side-effect management [6, 8]. Recent surveys reveal that 25% to 40% of cancer patients use cannabis, obtained from state-regulated dispensaries or illicit sources, primarily to manage symptoms like pain and anxiety [9].

PLWC often face heightened stress and anxiety due to their diagnosis and treatment. Cannabis is commonly used for symptom palliation, with approximately 40% of patients in the US, Canada, and Israel using it [10,11,12]. However, PLWC frequently lack guidance from their clinicians regarding appropriate dosages, consumption frequency, and specific product usage [13]. Clear communication regarding cannabis use between PLWC and healthcare providers is crucial for monitoring therapy outcomes, optimizing dosing amid potential drug interactions, reducing the necessity for external consultations, and educating healthcare providers to seamlessly integrate cannabis into existing treatment plans [14]. Despite the increase in legalization and normalization of cannabis, studies reveal a significant knowledge gap among healthcare professionals including understanding of cannabis-related recommendations for patients and evolving regulatory guidelines [15]. Healthcare providers frequently experience a lack of adequate knowledge regarding the use of cannabis by PLWC. Additionally, healthcare providers, including oncologists, face challenges in staying up to date with cannabis science research and providing effective communication to their patients due to their lack of training around MC usage [16, 17]. On the other hand, PLWC face challenges in initiating conversations with their providers regarding cannabis use because of the stigma attached to it [11]. In a survey of 1,592 individuals treated at a National Cancer Institute-designated Comprehensive Cancer Center, it was observed that although approximately one-third of cancer patients engaged in discussions about MC with their healthcare providers, a smaller fraction received actual recommendations or instructions on how to utilize MC from their healthcare providers [18].

Along with the increased use of cannabis among PLWC, there is a dearth of knowledge around patient-provider communication in this realm, suggesting a need for a comprehensive compilation of available evidence and identification of gaps. To our knowledge, this is the first comprehensive synthesis of the available evidence regarding patient-provider communication around cannabis use in oncology settings. The purpose of this systematic review is to understand the dynamics of patient-provider communication surrounding MC use in cancer care and identify urgent gaps to pave the way for effective communication on cannabis use for PLWC.

This systematic review aims to:

  1. 1.

    Assess how often patients disclose MC use to healthcare providers and the extent of medical advice given in cancer care.

  2. 2.

    Analyze healthcare providers' knowledge, beliefs, and practices regarding MC, including their comfort in making recommendations and discussing it with patients.

  3. 3.

    Examine factors affecting providers' reluctance to discuss MC, including the role of clinical evidence.

  4. 4.

    Identify barriers and information needs related to recommending and monitoring MC use in cancer patients.

  5. 5.

    Determine the training and information needs of healthcare providers on MC in oncology settings.

Methods

Overview

Healthcare providers’ communication of cannabis use among PLWC was explored using guidelines for reporting systematic reviews. The study team followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement to complete this report [19]. No pre-registration was performed for this systematic review. The screening process as well as the management of collected articles were conducted using the Covidence website (www.covidence.org). We chose a systematic review approach to provide a comprehensive and unbiased synthesis of the limited existing evidence on this topic. This methodology allowed us to uncover international evidence to evaluate the quality and findings of included studies, ensuring that our conclusions are based on high-level evidence to inform clinical practice and future research.

Eligibility Criteria

Articles were included in this systematic review if they were formally published research studies. The study population included PLWC and healthcare providers working in oncology settings. To ensure a comprehensive approach, the inclusion criteria were deliberately broad, aiming to encompass a wide range of relevant articles. The inclusion criteria for this review included (1) articles published from 2013- 2023, (2) studies related to humans, (3) published research studies, and (4) articles published in English. Exclusion criteria included: 1) articles published prior to 2013, (2) studies not related to humans, (3) review papers, experts' opinions, case reports, letters, or editorials and unpublished manuscripts, and (4) articles published in a language other than English.

Information Sources and Search Strategy

An experienced team of researchers developed comprehensive search strategies for three electronic scientific databases—PubMed, CINAHL, and EBSCO—on July 11–12, 2023. We used keywords and MeSH terms based on the Population, Intervention, Comparison, Outcomes, and Study Design (PICOS) Model to search for articles on PLWC and provider communication regarding cannabis use in oncology settings. The articles were searched using the keywords and MeSH terms “Cannabis,” “Information,” and “Cancer,” combined with the Boolean operators “AND” and “OR” to capture the study’s key concepts: cannabis use in cancer patients and their communication to healthcare providers in oncology settings. The detailed list of search strategies employed is depicted in Table 1.

Table 1 The Search Strategy of the Research
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Data Extraction and Quality Assessment

After retrieving articles from the three databases, three reviewers (AB, BD, and JG) independently screened titles and abstracts for relevance. Next, full texts of the remaining articles were examined and analyzed to ascertain their eligibility for inclusion. Disagreements were resolved through consensus. Articles were included if they reported data on PLWC and provider communication regarding cannabis use in oncology settings. Quality assessment of included articles was performed using the Johns Hopkins Evidence-Based Practice Model for Nursing and Healthcare Professionals [20]. This model grades studies based on study design on a scale from I (higher level evidence) to III (lower level evidence). Methodological quality was reviewed independently by AB, BD, and CF, with disagreements resolved by discussion or a fourth author (DV). Data on authors, publication country, title, purpose, design, provider type, variables, and major findings were extracted for comparison (Table 2).

Table 2 Study Characteristics from Included Research Articles
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Results

The flow diagram of the study selection process is provided in Fig. 1.

Fig. 1
figure 1

The process of screening articles based on the PRISMA 2020 flow diagram

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Of the 14 studies included, three were qualitative with sample sizes of 16 to 50 [21,22,23]. Whereas 11 were cross-sectional with sample sizes of 45 to 3,052; one cross-sectional study used a mixed method [15, 24,25,26,27,28,29,30,31,32,33] (Table 2). According to the Johns Hopkins Evidence-Based Practice Model for Nursing and Healthcare Professionals, all studies were level III evidence. Studies captured perspectives from both patients and providers: five among cancer patients and nine among oncology healthcare providers. Five studies were conducted in the United States, with the rest in Denmark (n = 1), Italy (n = 1), Australia (n = 3), Canada (n = 3), and New Zealand (n = 1) (Table 2).

The cross-sectional studies aimed to gather quantitative data on various aspects of MC, including patient behaviors and attitudes, such as willingness to discuss cannabis; the prevalence of use among PLWC and motives for usage; healthcare professionals' knowledge and attitudes in primary care and oncology settings; oncology fellows' preparedness to discuss MC; and the frequency and nature of cannabis consumption and information sources. The qualitative studies aimed to explore in-depth aspects of MC, including healthcare oversight and practices, oncologists' beliefs and practices, and patient access to adjuvant therapy with physician guidance. They also examined patient interactions and knowledge about medicinal cannabis. Through narratives and thematic analysis, the studies uncovered cancer patients' attitudes, barriers, and concerns, offering a comprehensive view of their experiences with MC.

Studies Reflecting Providers’ Perspectives

In a 2018 US survey conducted by Braun et al., among 400 medical oncologists, 79.8% discussed MC with patients, and 45.9% recommended it for cancer-related issues in the past year. The discussion rate was higher in the West (94.7%) compared to the South (68.9%), with recommendation rates of 84.2% in the West and 34.7% in the South. Oncologists seeing more than 60 patients per week were more likely to discuss MC. Among those discussing MC, 78% had patient-initiated conversations. Only 29.4% felt knowledgeable enough to make recommendations, and 56.2% of those recommending MC lacked confidence in their knowledge. While lacking consensus on MC as a primary pain treatment, over two-thirds supported its use as an adjunct to standard pain management [24].

In a 2021 Italian study by Filetti et al., an electronic questionnaire assessed cancer care professionals' knowledge and attitudes toward MC prescription. Out of 2,616 respondents, 475 (18%) were analyzed. Most were medical oncologists/hematologists (61%) and anesthesiologists/pain specialists (13%) focusing on breast (20%), gastrointestinal (29%), and lung cancers (26%). Most were familiar with MC (90%), having been asked about it by patients (79%) or caregivers (66%). Approximately half of the healthcare professionals reported receiving requests to prescribe MC, but only 29% had actually done so. Few cited legislative references, and there was a notable lack of knowledge regarding the comparative effectiveness and safety profile of MC. Factors increasing the likelihood of prescribing included the professional's age, patient requests, positive views on effectiveness, and familiarity with normative references [26].

In a 2019 survey at an Australian cancer hospital, Hewa-Gamage et al. evaluated the attitudes of 150 health professionals (32 nurses, 10 pharmacists, and 24 allied health workers) toward medicinal cannabis in cancer care. Sixty-two percent of the respondents reported patient inquiries about medicinal cannabis, but over half felt insufficiently informed about access (74%), evidence base (59%), and potential drug interactions (65%). Recommendations varied, with 34% in favor, 20% against, and 46% unsure. Despite awareness of legislative changes in Victoria, only 11% felt informed about accessing medicinal cannabis. Twenty-nine percent were knowledgeable about its evidence base and 20% about drug interactions. While 77% of medical practitioners would "consider" prescribing it, none had done so. Education and knowledge gaps were common concerns, with 62% unsure about recommending medicinal cannabis despite receiving patient inquiries [27].

In a 2020 study, McLennan et al. surveyed 103 oncology healthcare providers (HCPs) at the Tom Baker Cancer Center in Calgary to identify barriers and preferences regarding MC. Most respondents were female (75%), including oncology nurses (40%), radiation therapists (9%), and pharmacists (6%). About 75% were directly involved in patient care. Findings revealed that 69% had discussed cannabis with a patient in the past month, and 84% felt insufficiently informed. Barriers included monitoring patient use (54%), prescribing accurate doses (61%), and lack of research (50%). Fifty-three percent wanted more training on cannabis in oncology. Notably, 69% had patients disclose cannabis use, and 41% were asked for advice. Additionally, 59% referred patients to other HCPs, mainly oncologists (35%) and MC practitioners (33%). Twenty-three percent requested patients stop using cannabis, citing concerns about interactions, harm, or lack of efficacy. Despite limited knowledge, many HCPs engaged with patients on cannabis and expressed interest in professional training on its use in oncology [15].

Oldfield et al. (2020) surveyed 45 doctors in New Zealand oncology settings to explore experiences with cannabis as medicine. Findings revealed that 37% received patient requests for cannabis-based products, and 98% noted patients using illicit cannabis. About 84% had patients who requested cannabis prescriptions, primarily for pain, cancer, and nausea. Among consultants, 46% attempted prescriptions, and 25% of registrars attempted. Reasons for not prescribing included a lack of knowledge around evidence and understanding. Despite concerns, 52% expressed a likelihood to prescribe a pharmaceutical-grade cannabis product. Side effects reported included drowsiness, nausea, and psychotic symptoms, with 73% aware of pharmaceutical-grade cannabis products. Educational sources included CME sessions, journals, Ministry of Health website, and others. CME sessions were preferred for future education. Some doctors faced impediments, like cost and paperwork in prescribing [28].

Panozzo et al. (2019) conducted a study within palliative care settings to understand information-seeking and requests for medicinal cannabis in clinician-patient consultations. The aim was to characterize patients and carers initiating discussions and the clinical outcomes. Twenty-eight palliative care clinicians in three major hospitals in Victoria, Australia, completed case reports for 104 interactions discussing medicinal cannabis. Patients and carers initiated 93% of discussions, with 66% indicating multiple reasons for cannabis use, primarily for pain, nausea, and poor appetite. One in four sought cannabis for cancer control or cure. About 40% of discussions involved requests for medicinal cannabis, and 27% resulted in prescription or management of existing ones [29].

Patell et al. (2022) surveyed 189 trainees from 40 US oncology fellowship programs, assessing MC practices and knowledge. Fifty-seven percent discussed cannabis with over five patients in the past year, but only 13% felt sufficiently informed to make recommendations. Formal training, received by 24%, was linked to increased discussions and confidence (risk ratio: 1.37, 5.06; P < 0.002, P < 0.001). Participants viewed cannabis as a useful adjunctive therapy, with 91% discussing it during training, often initiated by patients and families (80%). Common information sources were peer-reviewed literature (30%) and colleagues' lectures/webinars (29%). Formal training correlated with more frequent discussions (risk ratio: 1.48; P < 0.001). About 54% believed cannabis was somewhat more effective than conventional therapies for anorexia or cancer cachexia. Concerns included infections in immunocompromised patients using combusted MC. Identified barriers were lack of clinical data, training, stigma, and regulatory policies [30].

In 2017, Zylla et al. surveyed 552 oncology providers in Minnesota to assess their practices, knowledge, and attitudes toward MC. The study aimed to understand providers' views, identify barriers to patient enrollment, and assess interest in a MC clinical trial for stage IV cancer. Of 529 eligible participants, 153 (29%) responded, with 68 registered in the Minnesota Medical Cannabis Program. Most respondents were medical oncologists or medical oncology nurse practitioners/physician assistants (82%) with many practicing in the community setting (67%). For a patient scenario, 65% recommended MC, 25% opposed, and 10% skipped the question. Barriers included perceived cost, inadequate research, uncertainty about side effects/benefits, and lack of FDA approval. Additional concerns were abuse/misuse, quality of cannabis in Minnesota, legal ramifications for providers and patients, social stigma, and health group restrictions. About 36% lacked confidence in discussing risks/benefits, with registered respondents having greater confidence (12%). 85% desired additional training, preferring written summaries (75%), online programs (51%), symposiums/conferences (32%), and newsletters (18%) [31].

In a 2022 Danish study, Buchwald et al. conducted qualitative research with 50 healthcare professionals, including oncologists, palliative care specialists, general practitioners, and nurses, on their perceptions of cancer patients inquiring about MC for adjuvant palliative therapy. Professionals discussed MC only when initiated by patients or relatives due to a lack of clinical evidence in palliative care. Oncologists hesitated due to the absence of RCTs and inquired only if the patient showed adverse effects. Palliative care physicians engaged upon patient or caregiver requests. Nurses felt constrained by the lack of RCTs, and primary care physicians avoided the topic due to knowledge gaps. Oncologists viewed the Danish MC pilot program as politically driven, and the Danish Medicines Agency’s control frustrated primary care physicians. Oncology and palliative care nurses faced dilemmas and conflicting policies. Some palliative care physicians were willing to prescribe MC as a last resort, emphasizing respectful communication, while oncology physicians, understanding patients' hopes, refrained from prescribing on principle [22].

Studies on healthcare providers' perspectives on MC in oncology show common issues. Providers frequently get patient inquiries but feel inadequately informed to recommend MC. In the US and Canada, many oncologists discuss MC but lack confidence due to insufficient evidence and training. European and Australian providers also face barriers like limited clinical evidence and policy constraints. Overall, there's a clear need for better education and guidelines to help providers address MC inquiries effectively.

Studies Focused on Patients’ Perspectives

Cousins et al. (2023) examined cannabis-related discussions among 3,143 adult radiation oncology patients in Michigan, using the Michigan Radiation Oncology Analytics Resource (M-ROAR) to capture medical record data on cannabis use, motives, administration modes, and frequency. Among patients, 2.9% (91 individuals) chose not to answer cannabis-related questions. Univariate findings indicated that patients over 50 were less likely to withhold answers as compared to younger patients (OR: 0.433; 95% CI: 0.272–0.718; P = 0.001), while those with curative intent were more open than those with palliative intent (OR: 0.580; 95% CI: 0.382–0.883; P = 0.011). Patients with prior radiation history were more likely to decline answers than those without radiation history (OR: 2.165; 95% CI: 1.416–3.310; P < 0.001). In the multivariable model, age (aOR:0.419; 95% CI: 0.251–0.700), treatment intent (aOR:0.539; 95% CI: 0.343–0.846), and prior radiation history (aOR:1.944; 95% CI: 1.222–3.092) remained significant factors influencing patients' willingness to discuss cannabis-related topics [25].

Weiss et al. (2021) studied cannabis use among US breast cancer patients, focusing on reasons, timing, information sources, satisfaction, safety perceptions, and physician discussions. Of 612 participants (age ≥ 18 years) from Breastcancer.org and Healthline.com communities, 42% used cannabis; 23% used it solely for medical reasons, while 77% used it both medically and recreationally. Sixty-four percent were very or extremely interested in MC. Among 302 seeking information, most were dissatisfied: only 6% found it extremely satisfying, while 25% were very satisfied, 44% somewhat satisfied, 19% minimally satisfied, and 6% dissatisfied. Thirty-nine percent discussed cannabis with their physicians, with 76% of these conversations initiated by patients. Older participants (≥ 66 years) were more likely to consult their physicians (87%) compared to younger groups (76% for ages 50–65 and 69% for < 50 years, respectively, p = 0.03). However, a notable 28% felt uncomfortable discussing cannabis with their physicians. Younger patients were more likely to view their physicians as supportive, with 72% of those < 50 years feeling very or extremely supported, compared to 52% in the 50–65 age group and 46% in the ≥ 66 years group, respectively (p = 0.03) [33].

Black et al. (2023) studied 46 gynecologic cancer patients, primarily with ovarian and uterine cancer, undergoing chemotherapy at Calgary's Tom Baker Center to assess cannabis use patterns. Among participants, 37% used cannabis, mainly for pain, anxiety, and insomnia, sourcing it from recreational dispensaries without prescriptions. About 50% hadn't discussed cannabis with their doctor, relying on retailers and friends/family for information. Over half were open to discussing cannabis if initiated by their physician. Non-users preferred friends/family and dispensaries for information. Only 8 of 17 current users had spoken to their oncologist about cannabis, and just 2 found their doctor helpful. Overall, 28.3% wanted to discuss cannabis with their doctor, while 56.5% would if the physician started the conversation, 41.3% if they provided useful information, and 10.9% if the discussion was non-judgmental [32].

In a 2021 Braun et al. study, 24 individuals in MC authorized states reported using it for symptom management and as a substitute for standard treatments, claiming antineoplastic properties. They self-experimented without formal medical advice, relying on non-medical sources. Most obtained MC certifications through brief meetings with unfamiliar professionals with limited access to quality clinical information and brief consultations. Discussions about MC were patient-initiated, and few received certifications from primary care providers or specialists. Many providers, though neutral, were reluctant to advise on MC [21].

Davis & Wilson (2022) conducted a qualitative study with 16 Australian cancer patients to explore attitudes and concerns about medicinal cannabis. Participants aged 36–82 experienced pain, poor sleep, nausea, anxiety, and depression from various cancer treatments. Due to COVID-19, they joined face-to-face or online focus groups and interviews. Common issues included sleep and pain concerns. Support from family and cancer support groups was generally positive, but some hesitated to discuss cannabis. Many did not disclose use to health professionals, citing systemic limitations and lack of GP support. They often turned to the internet or friends for information. Challenges included obtaining legal prescriptions and frustrations with GPs' limited knowledge about cannabis and its efficacy [23].

Studies on patients' perspectives on MC reveal that older patients are more likely to discuss it with healthcare providers, though there is dissatisfaction with the information and support received. Many patients rely on non-medical sources and are frustrated with limited professional guidance. Regardless of methods or sample sizes, a common finding is that patients often initiate cannabis discussions and lack comprehensive medical advice, highlighting the need for improved communication and education in oncology care.

Discussion

Studies reveal a complex interplay of attitudes, knowledge gaps, and communication challenges in MC use. Providers show limited knowledge and confidence despite interest in prescribing MC. Patients increasingly view MC as a complementary therapy but face challenges due to insufficient physician support, systemic constraints, and reliance on non-medical sources. This discussion highlights key findings and their implications for the use of MC in cancer care.

Limited Medical Guidance and Patient-Initiated Disclosures

Patients with cancer often initiate discussions and disclose their use of MC but receive minimal advice from their medical teams [21, 22, 29, 33]. Many clinicians feel insufficiently informed to make recommendations about MC, despite growing patient interest. This discrepancy between self-reported knowledge and clinical practice highlights a critical need for improved provider education and guidelines on MC.

Patient-Driven Information and Self-Experimentation

The study highlights that patients often rely on personal experimentation and anecdotal sources for MC knowledge due to a lack of formal medical advice [21]. This underscores the need for comprehensive, evidence-based resources to help patients make informed decisions about cannabis use. The risks of self-experimentation, especially among medically fragile patients on complex treatments, are understudied but significant.

Access and Prescription Practices

A key finding is the reluctance of healthcare providers, especially oncologists, to discuss MC due to a perceived lack of clinical evidence. None of the oncologist participants had prescribed cannabis, though some palliative care specialists and general practitioners had occasionally done so [22]. This suggests a potential role for specialists and underscores the need for more research and clinical evidence to guide prescription practices.

Patient Characteristics and Disclosure Patterns

The study shows that patients over 50, those with curative intent, and those with a history of radiation are more likely to discuss MC use [25]. Recognizing these demographics helps providers approach discussions in a way that respects patient preferences and addresses concerns related to symptom palliation and prior radiation history.

Healthcare Provider Perspectives and Barriers

The study findings emphasize that healthcare providers, including oncology nurses, radiation therapists, and pharmacists, encounter barriers in discussing MC. These barriers include a lack of knowledge, concerns about monitoring, dosing, strain selection, and limited research [15]. Providers clearly need more research, education, and training on MC to better assess treatment risks and benefits.

Perceived Benefits and Access Difficulties

Participants reported potential benefits of MC, like improved chemotherapy tolerance and symptom management, underscoring its value in cancer care [23, 32]. However, access challenges—such as legal barriers, high costs, and lack of information—pose significant obstacles [23, 32]. Addressing these issues is crucial to ensure that patients who could benefit from MC can access it safely and legally, with proper monitoring by their oncology team.

Uncertainty and the Need for Reliable Information

This review highlights PLWC’s frustration with the perceived lack of evidence, limited practitioner knowledge, and misunderstandings about MC [23]. Patients frequently turned to non-medical sources for information, emphasizing the need for accessible, evidence-based resources. While family, friends, and cancer support groups provide valuable support, mixed experiences with general practitioners highlight the need for standardized guidelines and provider education in this emerging field.

Significant gaps exist in education and communication about MC in cancer care. Patients often lack clinical guidance and rely on anecdotal sources [24]. Despite its potential to alleviate symptoms, federal illegality complicates patient-provider discussions [34]. Oncologists often feel unprepared to advise on MC, underscoring the need for enhanced education and motivational interviewing to improve dialogue [9]. Legislative changes like the States Reform Act may reduce stigma, but challenges such as a limited evidence base and societal stigma persist [34]. Cancer education professionals must engage in research and education to improve outcomes [35]. Continuing education for healthcare providers on MC is crucial, including workshops, seminars, online certification, case studies, peer-reviewed journals, and clinical trials [36]. Training in legal and ethical issues, combined with patient education, supports informed decision-making and helps navigate regulatory challenges [37].

Limitations

The study designs and outcomes varied widely, complicating data extraction and synthesis. Quantitative studies lacked validated measures of cannabis knowledge and attitudes, hindering direct comparisons. With the topic still emerging, existing evidence levels were low. Despite this, the review mapped current knowledge and identified evidence gaps and research opportunities. Some studies might have been missed due to differing interpretations of selection criteria. To address this, we used Covidence software, established clear criteria, and held meetings to discuss the selection process. Non-English studies and those published before 2013 were excluded to focus on recent research.

Conclusions

As interest in medicinal cannabis grows among people living with cancer, healthcare providers' knowledge, attitudes, and training on its use vary widely. With increasing legalization and cultural acceptance, it is crucial to invest in education for providers and promote non-judgmental, open communication with patients. Public health initiatives should also aim to de-stigmatize medicinal cannabis discussions among people living with cancer.