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Due to the controversial nature of this topic and the target audience (young people) it is important that the reader reads the complete answer and not
simply one paragraph or a few sentences. Taking one part of the answer out of context can lead to a misinterpretation of the intended message.
Paul Dillon speaks to thousands of students across Australia providing information on alcohol and drugs, particularly in relation to looking after
themselves and their friends. Some young people make contact with him to ask questions that they did not feel comfortable asking in front of their peers.
The Real Deal on Drugs allows young people to ask questions about drugs and provides them with access to accurate and up-to-date information.

We've been told that weed can cause mental health problems but I'm guessing that this is only if you use the drug a lot. Can smoking weed once have any lasting effects?

Cannabis, marijuana, weed, pot, grass, ganga, mull or whatever you want to call it is a drug that continues to be popular across the world. It is also a drug that causes people like me (who are trying to provide good quality information to young people) great problems because there are no simple answers to most questions that people have…

This is a particularly difficult question to answer… I certainly believe that there are some people who should never smoke cannabis - not even once!

Some people certainly have very frightening experiences the first time they try the drug and this is often the reason that they choose to never use it again! Only a couple of weeks ago I met a young woman who had used cannabis once and had to be hospitalised because of the effect that it had on her. Her parents went out for the evening and she and a couple of friends decided to experiment with smoking a bit of weed. Almost immediately, she experienced great anxiety and her first ever panic attack. She was convinced she was going to die and threatened to hurt those around her if they did not take her to a hospital. The effect was so extreme that she eventually had to be physically restrained and taken to the emergency department. She had still not fully recovered from the experience when I met her and was still seeing a psychiatrist who was trying to help her cope with the anxiety and panic attacks she continued to experience from time to time.

Was this a typical experience? Absolutely not. As I said, some people have an unpleasant or scary time the first time they use cannabis but this extreme response this girl experienced is highly unusual. It could have been due to the young woman having a pre-existing condition that was 'unlocked' when she smoked the drug, or it could have been caused by her not feeling totally comfortable about smoking and the anxiety that she felt became overwhelming when she got stoned…

As you said, we certainly know that the more often you use cannabis, the greater the risks, particularly when you are young and don't have a fully developed brain. Others, however, even when they use it once in a while, (although this isn't the norm) can develop major mental health problems as a result of their cannabis use (usually due to the 'unlocking' of a pre-existing condition, as has been discussed above). But, in all honesty, there are others who'll use cannabis for a period of time and then just get bored with it and never use it again and never experience problems… that's what makes what I do so difficult.

There are no definites, no easy answers – there is no way of knowing if you are going to be one of the people who has no problems with cannabis or great problems – like any drug, you can never know exactly what effect you will have. Every young person has to make a decision whether they believe the possible risk is worth it…

Of course, you also need to remember that cannabis is an illegal drug. If you get caught with it in your possession there are very real consequences, even if it is your first experience with the drug.

So can smoking weed once have a lasting effect? I would have to say most probably not for most people, but it is important for me to say that I have certainly had contact with a number of people whose lives have changed after smoking cannabis, in some cases, just the one time. Will smoking cannabis once ‘unlock’ a condition like schizophrenia or bi-polar? On the evidence we have, you would most probably have to say you would have to be incredibly unlucky for this to happen - as it appears to be regular use that causes the greatest problems. That said, a one-time use can lead to a terrifying experience, usually around anxiety or a panic attack, and it may be something you never forget!