Risks at a glance
While under the influence
- Memory, attention, reactionswork less wellwell established
- Risk of road accidentsabout 1.25 to 2.66 times higherwell established
- Anxiety, panic, confusionmore common with high THCwell established
- Heart attack in the first hourespecially with pre-existing conditionsearly indications
With frequent use over a long period
- Dependenceabout one in eleven peoplewell established
- Psychosishigher risk, especially for vulnerable peoplewell established
- Coughing and bronchitiswhen smokedwell established
- Memorylargely recovers after stoppingwell established
- Anxiety and depressionslightly increased riskcause unclear
- Lung cancer from cannabis smoke alonenot established
Well established: confirmed in many studies. Cause unclear: there is a link, but it is unclear what is cause and what is effect. Early indications: few data so far.
While under the influence
As long as THC is active, memory, attention and motor control work less well. This is well established. That is why the risk of road accidents rises: reviews put it at 1.25 to 2.66 times higher. Combined with alcohol, driving ability is impaired even more, and it can still be reduced when the intoxication already feels over.
The heart beats faster. Studies suggest that the risk of a heart attack rises in the first hour after use, especially in people with pre-existing conditions. The data on this are still limited.
Restlessness, anxiety, panic and confusion, even paranoid thoughts, are also possible. This happens more often with little experience and with high THC, but it can affect anyone. In some people, intoxication triggers a temporary psychotic episode.
With frequent use over a long period
Airways
People who smoke cough more often, bring up more phlegm and more often have chronic bronchitis. Tobacco in a joint does additional harm. Whether cannabis smoke alone promotes lung cancer has not been established; for one form of testicular cancer, however, studies do show a link.
Thinking and memory
Regular use mainly impairs memory. After stopping, these impairments largely reverse. Whether lasting damage remains is disputed.
Psychosis
The risk rises with the intensity of use. People who use cannabis and develop psychosis do so almost three years earlier on average than people who do not use it. Cannabis acts as a trigger in people who are already vulnerable. With high THC, the risk is particularly high.
Risk of psychosis compared with people who do not use cannabis
Anxiety and depression
The risk is slightly increased, but not in all studies. Whether cannabis is the cause, or whether people with anxiety or depression are more likely to turn to cannabis, is an open question.
Dependence
From weekly use onwards, the risk rises markedly. In Germany in 2024, about 1% of 18- to 64-year-olds met the criteria for dependence. How dependence develops is explained in the module How dependence develops.
How many people develop a cannabis-related disorder
About one in eleven people who have ever used cannabis. Among those who use it regularly, the proportion is higher.
Synthetic cannabinoids
There is no evidence of fatal poisoning from cannabis alone. Synthetic cannabinoids, which may be mixed into products of unknown origin, are a different matter: their effects are barely predictable, and there have been cases requiring intensive care as well as deaths.
Reducing the risks
The safest option is not to use cannabis. If you do use it, however, you can reduce the risks considerably. The following points come from international guidelines for lower-risk use; the BIÖG (Federal Institute for Public Health) recommends them to adults.
Reducing the risks
Start late or not at allThe later you start, the better. The brain matures until around 25.
Less THCThe more THC and the less CBD, the greater the risk of dependence and psychosis.
No smoking, no tobaccoSmoke harms the airways, and tobacco adds to the harm. Vaporising puts less stress on them. Do not inhale deeply or hold your breath.
Take care with ediblesThe effect comes on with a delay and is hard to predict. Taking more risks an unintended overdose.
Occasionally rather than dailyAt most once or twice a week. Daily use over a long period harms mind and body.
Take breaksIf your memory or concentration declines, use less or take a break.
Know where it comes fromWith cannabis of unknown origin, the active ingredient content is unclear and it may be contaminated. Synthetic cannabinoids are particularly dangerous.
Don’t mixAlcohol, tobacco and other substances increase the risks. If you take medication, ask a pharmacist or doctor first.
Don’t driveHow long you should wait is explained in the module Road traffic and the law.
Who should avoid cannabisDuring pregnancy and breastfeeding, and with psychosis in the family, cardiovascular disease or an addiction. More under Who should avoid cannabis.
The risk is highest when several factors come together, such as starting early, frequent use and high THC. If you find it hard to stick to these points, the self-test or a conversation with a counselling service can help.
Putting it in perspective
The risks grow with frequency, amount and THC content, with an early start and with existing mental health problems. The self-test shows where your own use stands. Who is better off avoiding cannabis altogether is explained in the module Who should avoid cannabis.
Sources
- Bundesministerium für Gesundheit (2017): short report “Cannabis: Potenzial und Risiken” (CaPRis)
- National Academies of Sciences (2017): The Health Effects of Cannabis and Cannabinoids
- drugcom.de (BIÖG): Drogenlexikon, entry Cannabis
- NIDA (2024): DrugFacts Cannabis
- DHS: Cannabis, Zahlen, Daten, Fakten (ESA 2024)
- cannabispraevention.de (BIÖG): Gesundheitliche Aspekte
- drugcom.de (BIÖG): Welche Safer-Use-Empfehlungen für weniger schädlichen Cannabiskonsum gibt es (für Erwachsene)?
- Fischer et al. (2022): Lower-Risk Cannabis Use Guidelines (LRCUG), International Journal of Drug Policy 99, 103381