Interest in cannabis-based medicines for mental health is growing. As more countries allow medical cannabis, more people are asking whether it could help with anxiety, depression or post-traumatic stress disorder (PTSD). Others want to know whether it has any role in problems with alcohol, opioids, tobacco or cannabis itself.
A recent systematic review and meta-analysis, published in the journal Psychiatry Research, set out to answer these questions. Researchers at UNSW Sydney brought together 200 studies of medicinal cannabinoids across ten mental health and substance use conditions.
Key Takeaways:
- The review included 200 studies. Of these, 95 studies with 66,698 participants had data that could be pooled in a meta-analysis.
- In clinical trials, medicinal cannabinoids were associated with a modest reduction in anxiety symptoms. The certainty of this evidence was very low.
- One small trial of 20 people found a reduction in PTSD symptoms. Larger studies are needed to confirm this.
- There was little or no effect on depression or ADHD, or on overall symptoms of psychosis. Small changes were seen in some symptoms of psychosis and Tourette syndrome, again at very low certainty.
- No benefit was found for alcohol, opioid or tobacco use disorders.
- People taking THC were more likely to stop treatment because of side effects than people taking a placebo. The authors conclude the evidence does not support cannabinoids as a first-line treatment for any of these conditions.
Why are people interested in cannabis for mental health?
Medical cannabis is now legal in many countries. Beyond chronic pain, mental health symptoms are one of the most common reasons people access the medication. There are also growing reports of people trying to manage problems with alcohol, opioids and other substances through medical cannabis.
Cannabis contains many active compounds. The two best-known are tetrahydrocannabinol (THC) and cannabidiol (CBD). They act on the body’s endocannabinoid system, which is involved in mood, stress and reward. This has led researchers to ask whether cannabinoids could be useful in mental health care.
The same research team published a review on mental disorders in 2019. It found scarce evidence that cannabinoids improve depression, anxiety, PTSD or psychosis. The new review updates that work and adds substance use disorders.
How are these conditions usually treated?
There are well-established treatments for all the conditions in this review. In the UK, these are guided by the National Institute for Health and Care Excellence (NICE).
- Anxiety and depression: talking therapies, such as cognitive behavioural therapy (CBT), and antidepressant medicines. These are often available through NHS Talking Therapies.
- PTSD: trauma-focused psychological therapies, such as trauma-focused CBT or EMDR. Medicines may also be used.
- Psychosis: antipsychotic medicines, psychological therapies and support from specialist mental health teams.
- ADHD: stimulant and non-stimulant medicines, alongside psychological and practical support.
- Tourette syndrome: behavioural therapies, and sometimes medicines, to help manage tics.
- Alcohol, opioid, tobacco and cannabis use disorders: psychological support, with licensed medicines available for some conditions. Free support is available through the NHS and local drug and alcohol services.
These treatments have a much stronger evidence base than cannabinoids. The review authors make this point directly.
What did the researchers do?
The team carried out a systematic review and meta-analysis. This means they searched for every relevant study, then combined the results where they could.
They searched four major medical databases for studies published up to May 2025. They looked for studies of adults given medicinal cannabinoids for:
- Mental health conditions: anxiety, depression, PTSD, psychosis, ADHD and Tourette syndrome
- Substance use disorders: alcohol, cannabis, opioid and tobacco use disorder
The treatments fell into three groups: pharmaceutical-grade THC (with or without CBD), pharmaceutical-grade CBD, and herbal medicinal cannabis.
The review included two types of study:
- 82 experimental studies. All were randomised controlled trials (RCTs), where people are randomly given either a cannabinoid or a comparison, such as a placebo. RCTs are the best way to test whether a treatment works.
- 118 observational studies. These follow people using cannabinoids in everyday life. They can show links but cannot prove cause and effect.
Two researchers rated how reliable each study was. The team then used a system called GRADE to judge how certain they could be about each finding. “Very low certainty” means the true effect could be very different from what the studies found.
What types of studies were included?
The trials were small. The typical (median) trial had just 48 participants. Most tested CBD-only products, and most gave the cannabinoid by mouth.
One finding is important for reading the results. Only 20% of the anxiety trials, and just 3% of the depression trials, were in people whose main diagnosis was that condition. Most measured anxiety or low mood as a secondary outcome in people treated for something else, such as chronic pain, cancer or multiple sclerosis.
What did the review find for mental health conditions?
Anxiety
Anxiety had the largest evidence base. Across 41 trials with 4,878 participants, cannabinoids were associated with a modest reduction in anxiety symptoms compared with a placebo or other treatment. However, the certainty of evidence was very low. Results varied widely between studies, and most people in these trials did not have an anxiety disorder as their main condition.
Post-traumatic stress disorder (PTSD)
A single small trial of 20 people found a reduction in PTSD symptoms. The evidence was rated as moderate certainty, but the authors note that one study this small gives a very imprecise result. Observational studies also reported lower PTSD symptoms over time, but these studies were at high risk of bias.
Depression
Trials found that cannabinoids had little to no effect on depressive symptoms (very low certainty). Some observational studies reported improvements, but these studies had no comparison group, so the changes cannot be put down to cannabinoids.
Psychosis
Cannabinoids had no effect on overall or negative symptoms of psychosis, such as low motivation. A small reduction in positive symptoms, such as hallucinations, was seen. All findings were very low certainty.
ADHD and Tourette syndrome
Two trials with 127 people found no clear effect on ADHD symptoms. Three trials with 138 people suggested a small reduction in Tourette syndrome symptoms. Both findings were very low certainty.
What did the review find for substance use disorders?
No observational studies of substance use disorders had data that could be pooled. All the findings below come from a small number of trials, and all were very low certainty.
- Alcohol use disorder: no difference between cannabinoids and placebo in overall symptoms or cravings.
- Cannabis use disorder: one trial found that overall symptoms were worse in people given cannabinoids than in those given a placebo. There was no clear effect on withdrawal or cravings.
- Opioid use disorder: no effect on withdrawal symptoms or cravings. No trial reported overall symptoms.
- Tobacco and nicotine use disorder: no difference between cannabinoids and placebo in overall symptoms or cravings.
What did the review find about side effects?
All medicines can cause side effects. Most of the safety findings in this review were very low certainty, because few trials reported them and the results were imprecise.
The clearest safety finding was for THC. Across 15 trials with 1,758 participants, people taking THC were more likely to stop treatment because of side effects than those taking a placebo. The odds were almost three times higher.
There were also less certain signals of more side effects with CBD, and of more serious side effects with THC and CBD combined. The authors say these signals are clinically important and should be carefully weighed in any decision about treatment.
How strong is the evidence?
The authors describe the overall evidence as very low certainty, with major limitations. These are important for understanding the results.
- Small, short trials. Most trials had few participants and short follow-up, so results are imprecise.
- Mixed results between studies. Studies used different products, doses, routes and ways of measuring symptoms. This makes pooled results harder to interpret.
- Wrong population for many questions. Much of the anxiety and depression evidence came from people treated for other conditions. It should not be taken as evidence of benefit for anxiety or depressive disorders.
- Different products in research and real life. Most trials used pharmaceutical products with lower THC doses. Many people who use cannabis for mental health use plant products with higher THC and less CBD.
- High risk of bias in observational studies. Most observational studies were at serious risk of bias. The improvements they report are changes over time, not proof that cannabinoids caused them.
- Few studies for substance use. Very few trials looked at alcohol, opioid or tobacco use disorders.
- Methods. One researcher extracted the data, with a second checking it. The authors note this is not the same as fully independent double extraction.
The authors identified 33 ongoing or unpublished trials, 17 of which are still running. These may provide better evidence in future.
What does this mean for patients in the UK?
In the UK, no cannabis-based medicine is licensed to treat any mental health or substance use disorder. Established treatments such as talking therapies and licensed medicines remain the recommended first options.
This review supports that approach. The authors conclude that the current evidence is insufficient to support medicinal cannabinoids as a first-line treatment. They note that some findings, particularly for anxiety, warrant further research. They also stress that higher-quality trials are needed before firm conclusions can be drawn.
In the UK, cannabis-based medicines can only be prescribed by a specialist doctor, on an individual basis, where there is an unmet clinical need. The specialist must consider the evidence, the possible risks and the person’s history, including any history of psychosis or substance use.
Looking after your mental health
If you are struggling with anxiety, low mood, trauma or your use of alcohol or drugs, speak to your GP or a qualified healthcare professional. Talking therapies and prescribed medicines are the established first-line treatments. You can also refer yourself to NHS Talking Therapies in England. In an emergency, or if you feel unable to keep yourself safe, call 999, go to A&E, or contact NHS 111 or a crisis helpline, such as Samaritans (116 123).
Curaleaf Clinic is a specialist medical cannabis clinic. To find out whether a consultation with one of our specialist doctors may be appropriate for your circumstances, you can complete our online eligibility check. All treatment decisions are made by a specialist on an individual basis after a full assessment.
Frequently asked questions
Does medical cannabis work for anxiety?
This review found a modest reduction in anxiety symptoms in clinical trials, but the evidence was very low certainty. Most participants were being treated for other conditions, such as chronic pain, rather than an anxiety disorder. Larger, better-designed trials are needed. Talking therapies and licensed medicines remain the recommended first-line treatments.
Can medical cannabis help with depression?
The trials in this review found little to no effect on depressive symptoms, with very low certainty. Very few trials included people whose main diagnosis was depression. If you are struggling with low mood, speak to your GP about established treatments such as talking therapies and antidepressants.
Is CBD safe for mental health?
No medicine can be described as completely safe. In this review, there was a less certain signal of more side effects with CBD than with placebo. People taking THC were more likely to stop treatment because of side effects. Any treatment decision should be made with a doctor who knows your medical history.
Can cannabis help with addiction?
This review found no benefit for alcohol, opioid or tobacco use disorders. In one trial, cannabinoids were linked to worse symptoms of cannabis use disorder. Free, confidential support for alcohol and drug use is available through the NHS and local drug and alcohol services.
Is medical cannabis legal in the UK?
Yes. Since November 2018, specialist doctors have been able to prescribe cannabis-based medicines in the UK. They are usually considered only where other treatments have not worked well enough. Recreational cannabis remains illegal.
Can medical cannabis be prescribed for mental health conditions in the UK?
No cannabis-based medicine is licensed for any mental health condition in the UK. A specialist doctor may consider an unlicensed product in some cases, after other treatments have been tried, following a full assessment. You can read about how our specialists approach anxiety, depression and PTSD on our condition pages.
