- When mixed, effects add up or mask each other. That is riskier than any substance on its own.
- Alcohol, sedating medication and other drugs are particularly risky.
- If someone is unconscious, has a seizure or breathing problems: call 112.
Why mixing is riskier
Effects can reinforce or mask each other. Then it is hard to predict how someone will feel shortly afterwards. According to drugcom, uncontrolled mixing is considerably riskier than using a single substance. The BIÖG therefore advises against taking cannabis together with other psychoactive substances such as alcohol or medication.
Alcohol
Most people with problematic cannabis use also drink alcohol in risky amounts. In a survey of young adults, cannabis intensified the effect of alcohol: participants felt more dazed and confused and found it harder to concentrate. The body’s warning signals are noticed less, and nausea, vomiting and circulation problems are common. Health Canada writes that impairment increases sharply when the two are combined. Separate rules apply to driving, see Road traffic and the law.
Tobacco and nicotine
Nicotine is quickly addictive and harms the heart and circulation. Anyone who smokes cannabis with tobacco risks becoming dependent on both substances. Tobacco in a joint is also considered a risk factor for a cannabis use disorder and increases the risk of lung cancer.
Medication
Together with sedating medicines such as opioids, benzodiazepines or some antihistamines, that is, some painkillers, sedatives and sleeping pills, the effects can add up. Cannabis can also change how the liver breaks down other medicines. More on this in the module Who should avoid cannabis. If you take medication regularly, ask at your doctor’s or at the pharmacy. Doctors are bound by medical confidentiality.
Other drugs
- Ecstasy and speed: dizziness, nausea, vomiting, up to circulatory collapse. Under THC, the body temperature raised by ecstasy stays high for longer.
- Ecstasy, speed, cocaine: anyone who mixes them with cannabis gets psychotic symptoms more often.
- LSD, mushrooms and other psychedelics: the effect intensifies, nausea and vomiting are common, and a psychosis can be triggered more easily.
- Unknown origin: cannabis from the black market can contain synthetic cannabinoids, which are considerably stronger. More on this in the module When it gets too much.
Warning signs
Seizures, dizziness, feeling faint, headache, sudden tiredness, pale and clammy skin, a fast pulse, unconsciousness, faltering or laboured breathing, blue lips.
In an emergency
1. Call 112. 2. If the person is unconscious, put them in the recovery position. 3. Do not leave them alone. 4. Tell the paramedics what was taken, as far as you know, and hand over any leftovers.
Don’t be afraid: doctors are bound by medical confidentiality. For questions about possible poisoning, including when a child has eaten something, the Informationszentrale gegen Vergiftungen Bonn helps in NRW on 0228 19240, around the clock.
Sources
- BIÖG (2025): information on cannabis, information sheet for members of cultivation associations
- drugcom.de (BIÖG, 2009): mixing substances, an experiment with an uncertain outcome
- drugcom.de (BIÖG, 2017): more unwanted effects from combined use of alcohol and cannabis (Lee et al. 2017)
- drugcom.de (BIÖG): cannabis and alcohol, expert comments
- mindzone (Caritas Bavaria, funded by the Bavarian State Ministry of Health, Care and Prevention): mixing substances
- Health Canada (2023): Cannabis impairment and safety risk
- Federal Ministry of Health (2017): summary report CaPRis
- cannabispraevention.de (BIÖG): health aspects
- Pharmazeutische Zeitung (2022): cannabis as an interaction partner, pages 1 and 2
- drugcom.de (BIÖG): drug emergencies
- Informationszentrale gegen Vergiftungen Bonn (Bonn poison information centre)