Cannabis / THC

What cannabis and THC are

The cannabis plant contains many cannabinoids. THC is the one that intoxicates. CBD (cannabidiol) is not intoxicating and CBN (cannabinol) is marketed mainly as a sleep aid; both have their own entries, this one is about THC and the whole plant. As a medicine, THC is available in several forms: as the pure substance dronabinol, as the synthetic derivative nabilone, as an oral spray with THC and CBD (nabiximols), and in cannabis flowers and extracts of pharmaceutical quality, whose content differs depending on the strain.

What is rated is the state of knowledge. It is broad: numerous randomized trials on pain, spasticity and nausea, an accompanying survey by the BfArM with around 21,000 reported treatments, and large epidemiological studies on the risks. More on pain can be found under Chronic pain, on sleep under Sleep & sleep hygiene.

How it works

THC activates the cannabinoid receptors CB1 and CB2. CB1 is found mainly in the brain and spinal cord, CB2 mainly in the immune system. These are the same receptors through which the body’s own endocannabinoids such as anandamide act. CBD, by contrast, does not activate them.

Via CB1, THC dampens the transmission of pain signals and muscle tension, counteracts nausea and stimulates appetite. The same target in the brain explains the high and the impairments in memory, attention and reaction. Desired effects and side effects therefore cannot be cleanly separated.

What the studies show

Whiting 2015: the big overview

The review evaluated 79 randomized trials on ten uses, from nausea through pain and spasticity to anxiety, sleep and psychosis. Only 4 trials had a low risk of bias. Most showed an improvement, but it was not statistically significant in all trials. On the pain scale from 0 to 10, scores fell on average by 0.46 points more than on placebo. For weight gain in HIV, sleep disorders and Tourette syndrome there was only low-quality evidence. Short-term side effects, including serious ones, occurred more often on cannabinoids.

Wang 2021: how large the benefit for pain is

The meta-analysis included 32 trials with 5,174 adults, 29 of them against placebo, with cannabis taken by mouth or applied to the skin and observation periods of 1 to 5.5 months. Pain fell on average by 0.5 cm on a 10 cm scale, with moderate certainty of evidence. Physical function and sleep quality improved very slightly to slightly, with high certainty; emotional and social functioning did not. In trials of three months or longer, dizziness was considerably more common than on placebo.

What users report: the BfArM’s accompanying survey

Between 2017 and 2022, doctors had to report anonymized data on statutorily insured patients who received cannabis. 16,809 complete data sets were evaluated. The main conditions treated were chronic pain (76.4 percent), then spasticity (9.6 percent) and loss of appetite and wasting (5.1 percent). In just under 75 percent of cases the symptoms improved, in 70 percent quality of life. One third stopped before a year was up, mostly because of lack of effect (38.5 percent), less often because of side effects (25.9 percent). Those who received flowers were on average 45.5 years old, more than two thirds male, rated the success higher and reported a euphoric effect three times as often. There was no control group; the BfArM stresses that the data do not replace clinical trials.

Where the data stop

• Small effects on pain. The relief averages about half a point on the ten-point scale. For individuals it can be more, on average it is little.
• Flowers without approval trials. The meta-analysis on pain covers only cannabis taken by mouth or applied to the skin, no inhaled flowers. According to the German federal government, cannabis flowers are prescribed without a marketing authorization under medicines law, without evidence tested in approval trials in patients. In the accompanying survey, the amounts of THC with flowers were far above all scientifically studied dosages.
• Sleep and appetite. Here the evidence is of low quality. In pain patients, sleep quality improved only slightly.
• Long-term data from therapy. The controlled trials ran for a few months at most. What years of medical treatment achieve is shown only by observational data without a comparison group.

Status, approval and legal

Since April 1, 2024, cannabis is no longer a narcotic in Germany. The Cannabis Act split the rules into two laws. The Medical Cannabis Act (MedCanG) covers flowers, extracts and THC including dronabinol for medical purposes. Only physicians may prescribe, not dentists or veterinarians; it is dispensed only in pharmacies on prescription, since 2024 on a normal prescription instead of a narcotics prescription. Statutory health insurance pays after approval by the insurer.

A tightening is planned. The government draft of December 3, 2025, justifies it by the fact that imports of medical flowers rose by 170 percent from the first to the second half of 2024, but prescriptions reimbursed by statutory insurers by only 9 percent, and that telemedicine platforms arrange flowers after an online questionnaire without personal contact with a doctor. In future, flowers are to be prescribed only after personal contact in the practice or on a home visit, and follow-up prescriptions without new contact only if such contact took place in the last four quarters. Mail-order delivery of flowers to consumers is to be banned. As of November 2026, the law has not been passed; the Medical Cannabis Act applies in the version of June 20, 2024.

For adults aged 18 and over, the Consumer Cannabis Act (KCanG) regulates handling without a prescription. It is permitted to carry up to 25 g, up to 50 g at one’s place of residence and up to three live plants. Advertising and sponsorship are banned. Use is banned in the presence of minors, public use in and within sight of schools, children’s playgrounds, children’s and youth facilities and publicly accessible sports facilities, with the line of sight ending after 100 m, and in pedestrian zones between 7 a.m. and 8 p.m.

In road traffic, a limit of 3.5 ng/ml THC in blood serum applies; anyone who reaches it commits an administrative offence, and in combination with alcohol a higher fine is imposed. THC from taking a prescribed medicine as directed is exempt. In sport, according to the WADA list 2026, all natural and synthetic cannabinoids are banned in competition, with the exception of CBD.

Safety

Dependence is the most common serious risk. According to a meta-analysis of 21 studies, 22 percent of people who use cannabis meet the criteria for a cannabis use disorder and 13 percent those for dependence. In young people who use weekly or daily, the risk of dependence rises to 33 percent.

The second major risk concerns mental health. In the European EU-GEI study with 901 people with first-episode psychosis and 1,237 controls, daily use was associated with 3.2-fold and daily use of high-potency strains with at least 10 percent THC with 4.8-fold higher odds of psychosis. Assuming a causal relationship, 12.2 percent of first-episode psychoses could be prevented without high-potency cannabis, 30.3 percent in London and 50.3 percent in Amsterdam.

In the therapy trials, dizziness, dry mouth, nausea, fatigue, euphoria, confusion and balance problems are common, and serious side effects also occur more often than on placebo. For flowers, the BfArM urges that the risk of misuse and dependence be considered already when planning therapy, because of the high amounts of THC, the high proportion of men and the younger age of those treated.

Sources

• Whiting PF et al., JAMA 2015 – systematic review and meta-analysis, 79 trials on cannabinoids in medicine
• Wang L et al., BMJ 2021 – meta-analysis, 32 trials on medical cannabis for chronic pain
• BfArM 2022 – final report of the accompanying survey under § 31 (6) SGB V (German Social Code, Book V)
• Di Forti M et al., Lancet Psychiatry 2019 – cannabis use and psychosis in Europe (EU-GEI)
• Leung J et al., Addict Behav 2020 – meta-analysis on the prevalence of cannabis use disorders
• Medical Cannabis Act (Medizinal-Cannabisgesetz, MedCanG)
• Consumer Cannabis Act (Konsumcannabisgesetz, KCanG)
• Bundestag, printed paper 21/3061 of December 3, 2025 – draft of a First Act Amending the Medical Cannabis Act
• German Road Traffic Act (StVG), § 24a – THC limit
• WADA – Prohibited List 2026, S8 cannabinoids