Cannabis is the drug most teenagers encounter first, and it has a reputation among young people for being low-risk, close to harmless. That reputation has not kept pace with the research. A large study published in February 2026 in JAMA Health Forum followed more than 463,000 adolescents and found that those who reported cannabis use in the past year had roughly double the risk of later developing a psychotic or bipolar disorder, compared with teenagers who did not use it, even after accounting for prior mental health history and other substance use.
This is not a reason to panic if your teenager has tried cannabis once at a party. It is a reason to take the subject seriously, know what the evidence actually says, and keep the conversation open rather than closed.
What the research actually shows
A few things are worth being precise about, because this is an area where exaggeration undermines trust, and so does minimising.
The risk is clearest for mental health, and it rises with how early and how much a teenager uses. The adolescent brain is still developing, broadly into the mid-twenties, and the evidence consistently points to younger, heavier use carrying more risk than occasional use starting later. The same 2026 study found elevated risk not only for psychosis and bipolar disorder, but also for depression and anxiety disorders, though the size of the effect was smaller for those.
It can be addictive. Cannabis use disorder is a recognised condition. Some people who use cannabis regularly find it hard to stop, and if they do try to cut down or quit, they can experience real withdrawal symptoms: irritability, trouble sleeping, anxiety, low mood, and reduced appetite. This surprises a lot of people, because cannabis is often talked about as if dependence does not apply to it the way it does to other drugs.
It affects memory, attention, and school performance. Regular use, especially when it starts early, is associated with more school absences, lower grades, and young people leaving education earlier than their peers who do not use. This tends to improve after stopping, but while someone is using regularly, it is a real cost.
It is not safe to drive under the influence of cannabis. It roughly doubles to triples the risk of a car accident, and combining it with alcohol increases that risk further.
The association with worse mental health outcomes does not mean cannabis causes every case. Researchers are honest that the studies show a strong statistical association and a biologically plausible mechanism, not absolute proof that cannabis alone causes every diagnosis that follows it. Some young people use cannabis because they are already struggling, and the substance use and the underlying difficulty can reinforce each other. Either way, the practical message for parents is the same: cannabis use in a teenager who already seems low, anxious, or is showing early signs of something else is worth taking seriously rather than writing off as experimentation.
A few specific myths worth correcting
“Young people are less at risk than adults.” The opposite is closer to true. Younger age at first use, and heavier use, are both associated with higher risk, largely because the brain is still developing.
“You can’t get addicted to weed.” You can. Cannabis use disorder and withdrawal are both real and documented.
“It makes you more interested in sex.” Most evidence points the other way. Long-term users often report lower interest, and in males it can affect sperm production and the ability to get an erection.
“It gives you more energy and motivation.” Regular users typically report the opposite: lower energy, lower motivation, and school or work performance suffering as a result.
How to talk to your teenager about it
This works better as an ongoing, low-key conversation than a single big lecture. A few things that tend to help:
- Lead with curiosity, not accusation. “What do your friends think about weed?” opens more doors than “Have you been smoking?”
- Share what you actually know, without exaggerating. Teenagers are good at spotting scare tactics and will tune out if the facts feel inflated. Stick to what the evidence says.
- Acknowledge that it is common and that trying it once does not make someone a drug user. The goal is honest risk information, not shame.
- If your teenager discloses regular use, resist a big reaction in the moment. A calm, “Thanks for telling me, I want to understand what’s going on,” keeps the door open for more conversation than a punishment-first response.
- If you suspect regular use, particularly alongside signs of low mood, anxiety, or withdrawal from friends and activities, it is worth talking to your GP or a school counsellor about next steps. Our piece on who can actually help, and what confidentiality means explains the realistic options and how privacy typically works with each one.
If you are supporting a teenager through this and the picture includes thoughts of self-harm or suicide, treat that as urgent. Contact your local emergency number, or Find A Helpline for a free, confidential crisis line in your country.
