Does cannabis increase the risk of psychosis?

Cannabis use can increase the risk of psychotic illness. According to the BIÖG, studies show that people who use regularly and over long periods are more often affected by psychosis, and a high THC content has an additional negative effect. Whether cannabis actually causes psychosis is not proven by this. For you, this means that the risk should be taken seriously, and whether you yourself belong to the more vulnerable group cannot readily be said.

What the state of research shows

The Bundesinstitut für Öffentliche Gesundheit (BIÖG) writes that people who use cannabis more often develop psychosis than people who do not. In psychosis, a person temporarily loses touch with reality and develops hallucinations and delusions. The BIÖG also notes that several risk factors are usually involved in the development of a mental disorder.

No single figure for your personal risk can be derived from this. The BIÖG names age, frequency of use, THC content and an inborn predisposition as factors.

High THC content and psychosis risk

An analysis reported by drugcom concludes that cannabis with a high THC content roughly doubles the risk of psychotic symptoms. The BIÖG classes varieties with a THC share above 10 per cent as having a high THC content, and writes that people who consume cannabis with a high THC content are probably more likely to suffer from an anxiety disorder, even if they do not use it so often.

Factor	What the sources report
Cannabis with a high THC content	Roughly double the risk of psychotic symptoms (drugcom)
Use among 12 to 19-year-olds	According to the report, 11 times higher risk of a psychotic disorder (drugcom)
Frequency and age	The harmfulness depends on both (cannabispraevention.de)
Predisposition	With an inborn predisposition, even small amounts can be enough (cannabispraevention.de)

Age and frequency of use

According to the BIÖG, the harmfulness of cannabis depends on the age of the person using it and on how often they use it. Young people are particularly at risk, because their brain is still in an important stage of development. According to the BIÖG, important remodelling and maturation processes take place in the brain until around the age of 25, which cannabis can disrupt, and this increases the risk of mental illness.

According to drugcom, one analysis of young people aged 12 to 19 reports an 11 times higher risk of a psychotic disorder when they use cannabis. These are figures from a single study, which cannot be transferred one to one to every person.

Predisposition is a separate factor

Not everyone reacts the same way. The BIÖG writes that for people with an inborn predisposition to psychosis, even small amounts of cannabis may be enough to trigger one. If you know of cases of psychosis in your family, you can discuss this with a doctor before using cannabis.

A predisposition is often impossible to judge on your own, which makes it all the more important to take changes in your own experience seriously and discuss them with a doctor.

What the link does not prove

The link between cannabis and psychosis is statistical. This means that the two occur together, but it does not necessarily follow that one causes the other. The BIÖG also names it as possible that people with a tendency towards psychosis turn to cannabis more often. Drugcom states that there is no cannabis psychosis as a separate condition. Cannabis is, however, seen as a possible stress factor in people who are already vulnerable. The DHS adds that with heavy use, existing mental illnesses can worsen and dormant psychoses can break out again.

Take warning signs seriously

When thinking, perception or behaviour change noticeably, this belongs in medical hands. This applies especially when new fears, thoughts of persecution or unusual perceptions appear. Do not wait for it to get better on its own. Contact a GP practice or the out-of-hours medical service, and in acute danger call the emergency number 112.

The first doctor’s visit: what to mention

For a good assessment, information about your use is important. Be honest about how often and in what amount you use, since when this has been the case, and whether anything has changed, for example in your sleep, concentration or mood.

Pre-existing conditions and mental illnesses in the family also belong in the conversation. A note with your questions helps you not to forget anything at the appointment. Ask, for example, which warning signs are important and when further investigation is needed.

• Amount and frequency of use over the last few weeks
• Changes in mood, sleep, thinking or perception
• Pre-existing conditions and medication you take regularly
• Mental illnesses in the family

Prevention: start late and keep use low

The BIÖG writes that young people should not use cannabis at all, for health reasons. Anyone who nevertheless uses cannabis can reduce how often they use, pay attention to the THC content and plan breaks. Parents and specialists find material on these questions under youth protection.

Your surroundings matter too. If you notice that friends are running into problems with their use, you can seek a conversation early and point them to help.

When relatives should look more closely

Pay attention to patterns that repeat over time, as well as to individual events. Among the typical signs of addiction, the BIÖG names withdrawal, mood swings and giving up interests. If you notice this in someone, an open conversation is worthwhile.

According to drugcom, problematic use usually starts well before dependence. What matters most, therefore, is whether negative consequences have already occurred. These include problems at school, in training or in relationships. These signals are a better reason for a conversation than the question of how much someone uses.

Cannabis and psychosis: what you can keep in mind day to day

Anyone who suspects an increased risk for themselves should discuss their use with a doctor. A diary of use and how you feel can show patterns.

If mental illnesses already exist, the question of cannabis belongs in medical treatment. Anyone taking medication should talk to the doctor about possible interactions.

What you can do now

Think honestly about how often and at what age you use, and whether there are pre-existing conditions or psychoses in your family. Raise this with your GP, especially if you notice changes in yourself. For questions about your own use, the Sucht & Drogen Hotline can be reached on 01806 313031 (calls are charged, daily 8 a.m. to midnight), and a local addiction counselling service also offers advice. More on the connection is in the overview of the studies and in the article on the young brain.