Well, being predisposed for schizophrenia or certain other mental illnesses
can put you at a higher risk of having a psychedelic (or some other drugs, such as cocaine) trigger that mental illness, so I would suggest doing a lot of research, starting very cautiously with small doses, and choosing an appropriate first-timer psychedelic if you decide to go ahead and try one. How old are you? The reports of people for whom schizophrenia was triggered by psychedelics tend to be at around the age that schizophrenia onset usually occurs without psychedelics, normally around early adulthood. But according to the reading I've done, triggering mental illness by the use of psychedelics is not nearly as common as the media and War on Drugs etc would have us believe. And some researchers have concluded that there was no evidence that those people wouldn't have gotten schizophrenia even if they hadn't used psychedelics, (and that if the onset occurred near the time of the use of psychedeclic it was likely a non-specific trigger). However, I don't think that the fact that MDMA or marijuana didn't cause any symptoms of mental illness for you is a reliable indicator that you will be fine with psychedelics, they are not very similar. I do have friends who have schizophrenic or bi-polar parents and they used psychedelics with no problems, but that doesn't mean that you aren't at any risk. But I know a lot of drug users and the only person I know who had schizophrenia onset in connection with drug use was doing copious amounts of cocaine. Read up on the effects you are going to experience with the psychedelic you choose, and choose something that isn't TOO intense and that is generally reliable (like mushrooms or LSD as opposed to, say, ayahuasca or datura). Try maybe 1/2 a normal dose the first time, that should still be plenty strong. And make sure you are with people you trust and are really comfortable with in a private, secure, positive environment. "Set and Setting", one's mindset and surroundings, are very important with psychedelics, especially for a first-time experience and especially for someone who may be predisposed to mental illnesses. Good luck and let me know if you need any help researching things or have any other questions. It's also perfectly ok to decide that maybe it isn't worth it for you to try psychedelics at this time - go with your intuition