From what I've read and experienced the above is correct, it can cause short psychotic episodes even in people not prone to them. Though usually this is in cases of abuse. I also saw first-hand that in people that already have an established psychotic disorder, even normal use can trigger episodes. Speed is much worse for this but MDMA also has this potential. I also suspect that amphetamine abuse (and by extension, perhaps MDMA) can worsen an established psychotic disorder long-term. This I do not know for sure because it's possible that even without the drugs it would have gotten worse but I know two mates of mine, brothers, went downhill exponentially fast as soon as they started using amps and coke. Their symptoms were relatively stable for about 4-5 years until they started on a serious binge. It all came crashing down in 6 months. One needs to take about 6-7 different meds a day just to be able to have anything approaching a normal life. The other one will never have anything approaching a normal life, but he still uses speed as well so yeah. They are 24 and 27 years old now, they were 18 and 21 at that time
In general I would strongly discourage the use of amphetamines if someone has a (suspected) pre-existing psychotic or severe anxiety disorder. There are other mental disorders where the same applies but a bit too much to list. One could make a case that drug use in general is to be discouraged when there are pre-existing mental disorders but that differs from person to person and from drug to drug. To conclude I would like to point out that this is not meant as a horror story. When used wisely, certain drugs can be used long-term and without much influence on the user. Hundreds of millions of people are proof of this. But when mental disorders come into play, certain drugs can become real dangerous to abuse or even use. If you suspect or know you have some psychological issue, research the hell out of it and weigh your choices when it comes to drugs 10 times more than you already should. When in doubt ask a professional first or just don't do it. Don't take risks when it comes to this, please