In this survey study, primary brain tumor patients physically attending the neuro-oncology outpatient clinic between August and October 2023 could be included. The medical ethics committee waived this study for the Medical Research Involving Human Subjects Act. All participants signed informed consent. Eligibility criteria included patients aged 18 years or older with either a radiological suspicion or a confirmed diagnosis of a primary brain tumor at any phase of the disease. Patients who were unable to read or understand Dutch were excluded. Those unable to complete the questionnaire for another reason, such as a significant language impairment or an inability to write or inability to visit the outpatient clinic, did not participate. Questionnaires could not be filled out by a proxy.

The questionnaire was completed by 102 people. We excluded 2 people with a secondary brain tumor, resulting in a total of 100 patients, of whom 79% had a glioma diagnosis and 11% had a meningioma. Fifty-one (51%) patients had used cannabis during their lifetime, with 14% currently using cannabis. Of the complete group, 19% currently or previously used cannabis for tumor-related reasons, including symptom relief (n = 14; 74%) and presumed effect on the tumor (n = 8; 42%), indicating that some patients (3 patients; 16%) used it for multiple therapeutic purposes. Mean age for never-users was 54 years old (SD 14), for current recreational users 31 years old (SD 6.6), and for current tumor-related users 57 years old (SD 11). See Table 1 for all demographics.

Table 2 displays details on cannabis use in prior and current users. Of the current cannabis users, most patients (n = 9; 64%) used it daily, 57% (n = 8) used it for symptom relief and 43% (n = 6) used it for presumed effects on their tumor. Tumor-related prior or current users mostly used oral forms of cannabis (n = 15; 79%). Of patients using cannabis for tumor-related reasons, 21% (n = 4) were unaware of the components of their cannabis. Patients (had) used doses ranging from 12 to 320 mg CBD and between 60 mg THC and 0.5–5 joints per day, whilst 42% (n = 8) of current users did not know the dose they were using (data not shown; results based on a combination of questions 11 and 13 regarding cannabis components and dose).

Among prior users (n = 37), 25 people (68%) did not select one of the provided multiple choice options for stopping cannabis. Four individuals (11%) did not provide any reason, while 18 (49%) stated a form of “no longer interested,” one person stopped due to their job, another due to their diagnosis, and one reported they “simply stopped” (data not shown).

For tumor-related users, the symptoms that were reported as most frequently improved through cannabis were sleep, anxiety, worrying, and depressive symptoms, see Figure 1. Only 2 symptoms (cognition and appetite) worsened a little as reported by one person, no people reported a substantial worsening of symptoms. Some patients did not respond to certain symptom-related questions, with nonresponses ranging from to individuals for the anxiety, worrying, and depressive symptoms items to 5 people for the items on muscle/spasms, appetite/weight, and epilepsy. The most frequently reported adverse events were drowsiness, dry mouth, and dizziness, see Figure 2. One person did not respond to the adverse event question.

In this study of Dutch primary brain tumor patients, a little over half of patients reported past or current cannabis use, with 14% actively using it. Of all brain tumor patients currently using cannabis, 57% used it for symptom relief and 43% used it for presumed effects on their tumor.

The percentage of current cannabis users in our cohort was comparable to that of Dutch cancer patients undergoing systemic anticancer treatment,¹² but higher than in the general population. In 2021, an estimated 1.3% of European adults aged 25–64 used cannabis daily, and in the Netherlands, 6.4% of adults used it in the last month.⁷ Cannabis use in the Netherlands seems less prevalent than in the USA, where 14% of adults aged 26 or older used cannabis in the past month.¹³ Similar to these differences in the general population, the percentage of current cannabis users was lower in our cohort than among 73 glioma patients in Florida, where 22% currently used cannabis.² Although cannabis use among Dutch patients seems less prevalent than in the USA, cannabis users still comprise a significant portion of patients.

In a comparable German study of 102 patients with an intracranial glioma, 14% used alternative therapies, although it is unclear if this included cannabis or other substances.¹⁴ Another survey among 277 French glioma patients found that 9% used medication without a prescription, and 22% used a food supplement.¹⁵ The authors did not specify the nature of these substances, but cannabis could potentially fall under either category. To our knowledge, no specific data exist on the use general complementary therapies among Dutch neuro-oncology patients.

Interestingly, a significant percentage of patients, including tumor-related users, first used cannabis before their tumor diagnosis. This could be attributed to the more relaxed regulations in the Netherlands and the high rate of lifetime cannabis experimentation, which stands at 28.8% in the general population.⁶ It is plausible that patients who had previously tried cannabis were more open to using it again following their brain tumor diagnosis.

Of all brain tumor patients currently using cannabis, most people use it for symptom relief. The most commonly reported improvements were in sleep, anxiety, worrying, and depressive symptoms. Patients reported cannabis use to be beneficial with one patient reporting only a little worsening of cognition and appetite, whereas most other symptoms either improved a little or improved a lot. Of note, some answers were missing. Possibly, patients did not experience a specific symptom such as epilepsy or cognitive problems prior to starting cannabis so therefore did not know cannabis’ effect on it, did not remember the effect if they were prior users, or had a lack of time as they completed the questionnaire in the waiting room. Nevertheless, our findings align with the findings in the Florida glioma cohort, where patients also reported an improved ability to cope emotionally, to relax, and to sleep. However, that study only reported 7 symptoms and they did not report if any symptoms worsened.²

Our findings on perceived improvements in sleep corroborate a recent meta-analysis in patients with sleep disturbances, which found modest evidence for small benefits of cannabis on sleep quality and sleep disturbance among chronic pain patients.¹⁶ However, they did not differentiate between different cannabis components.

Additionally, patients in our cohort frequently reported improvements in mental health symptoms, ie, anxiety, worrying, and depressive symptoms. This corroborates a 2019 meta-analysis among patients with various diseases¹⁷: THC did not affect depressive symptoms but improved anxiety, though the evidence was graded low-quality and the effects were small. Conversely, another meta-analysis shows that acute administration of THC induced both anxiety and depression in healthy volunteers.¹⁸ CBD, however, shows less conflicting results and might be promising in the management of anxiety based on animal research and some small studies in healthy volunteers and patients with an anxiety disorder.¹⁹

A significant part of current cannabis users also reported using it for presumed effects on their tumor. This is more than in the Florida glioma cohort, where only 3 out of 73 patients independently reported this reason,² but aligns with a Dutch study involving 153 patients with extra-cranial cancer, where 46% used cannabis for presumed antitumor effects.¹²

While some preclinical studies have suggested potential benefits on cell growth, apoptosis, and angiogenesis, clinical evidence remains insufficient with just one placebo-controlled clinical trial.^20,21 In the randomized, double-blind, and placebo-controlled part of this phase 1b study involving 21 patients with a recurrent glioblastoma, a CBD:THC spray alongside Temozolomide resulted in a more favorable survival.²¹ However, the small sample size, favorable demographics, 2 early deaths in the placebo group, and unavailable molecular information complicate the interpretation of the results.^4,21

In our cohort, few adverse events were reported, with the most commonly reported being drowsiness, dry mouth, and dizziness. Given the observational design of our study, the self-reported adverse events could possibly be attributed to other medications or treatments. Moreover, 21% of patients were undergoing chemotherapy at the time of questionnaire completion, and 7% were receiving chemoradiation, which may have also contributed to these reported adverse events. However, these findings are consistent with known adverse events of medical cannabis, which are common and include somnolence, dizziness, dry mouth, and nausea.²² The occurrence of adverse events might depend on various aspects such as the cannabis components and dosage of cannabis used. The few self-reported adverse events in our study could be due to the preferred use of CBD among participants. CBD has a more favorable adverse event profile than THC with few serious adverse events, and is generally well-tolerated.²³

We found that a considerable proportion of patients were unaware of the constituents of their cannabis. Of the patients using cannabis for tumor-related effects who did know the constituents, the majority favored CBD-dominant products. Doses of cannabis varied greatly among those who knew the dose of their cannabis product. These findings underscore the need for more comprehensive information regarding the distinct effects of both CBD and THC and of different doses.⁵

A considerable proportion of Dutch people with a primary brain tumor use cannabis, with the most frequently reported reasons being symptom relief and presumed beneficial effects on tumor growth. The user rate reflects the patients’ needs for randomized controlled trials into the effects of cannabis, mainly on sleep, mental health, and tumor effects.

Supplementary material is available online at Neuro-Oncology Practice (https://academic.oup.com/nop/).

We thank Myra E. van Linden, Mathilde C.M. Kouwenhoven, and Anine H. Stam for their role in data collection.

Vera Belgers, Department of Neurology, Amsterdam UMC location Vrije Universiteit Amsterdam, Amsterdam, The Netherlands; Cancer Center Amsterdam, Brain Tumor Center, Amsterdam, The Netherlands.

Niek A Rietveld, Department of Neurosurgery, Amsterdam UMC location Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.

Philip C de Witt Hamer, Department of Neurosurgery, Amsterdam UMC location Vrije Universiteit Amsterdam, Amsterdam, The Netherlands; Cancer Center Amsterdam, Brain Tumor Center, Amsterdam, The Netherlands.

Johanna M Niers, Department of Neurology, Amsterdam UMC location Vrije Universiteit Amsterdam, Amsterdam, The Netherlands; Cancer Center Amsterdam, Brain Tumor Center, Amsterdam, The Netherlands.

None declared.

This study was funded by the Anita Veldman Foundation (CCA2018-2-17). The funder was not involved in the design or interpretation of this study.

All authors have seen and approved the final manuscript. Conceptualization: VB, JMN, PCdWH; Data collection: NAR, VB; Descriptive analyses: VB, Writing: Original draft: VB, Writing: Review & editing: all authors.

Data of this study is not publicly available due to privacy regulations.