Mental health issues tend to arise with long term use of psychostimulants.

Every time you use a drug like speed, crystal, ice or meth it creates a chemical reaction in your brain. Once it wears off, your serotonin and dopamine levels in your brain drop, often below their normal levels. That's why you feel lousy and often depressed when coming down. Given enough time between use, most brains "restock" their normal chemical levels naturally. But if you use again, these levels will surge back up and then crash again.

Over time, however, your serotonin and dopamine levels may drop well below their normal level and stay there. That's why some users believe they are unable to experience feelings of happiness, satisfaction or enjoyment without methamphetamine. The more you use and the longer you use, the longer it may take for your mood chemistry to even out at high enough levels.

Some people will already have mental health issues before they start using. Depression, anxiety, schizophrenia and attention deficit disorder are not uncommon in Australia. Psychostimulants have an uncanny ability to bring out compulsive and/or psychotic behaviour. When using you can bring on psychosis (you can't tell the difference between what's real and what's not). Psychosis and compulsive behaviour can come on slowly or very quickly and are usually fear driven.

You may discover that methamphetamine provides relief from some of your troubles - like you feel less depressed or less anxious while speeding. This is called "self-medicating", but this relief is only temporary. Often the symptoms can return even more strongly, during or after the come down, making the symptoms even worse.

For those with more serious mental health conditions (like schizophrenia or psychosis) their symptoms will get more severe while using speed.