One important point in this subject is that the fact that two things are correlated or linked does not necessarily mean that one is the cause of the other.

I read a study some time ago which suggested that «people who read the composition of the food have less problems with obesity». Possibly, people who read food labels are more health-conscious and have better dietary habits. However, simply reading a label is not enough to keep one healthy or in good shape.

Here are more examples of events associated, but not necessarily caused one by the other. 

This idea is crucial when discussing about drugs and mental health. In the model used to explain schizophrenia, there is a susceptible or pre-morbid personality and various «stressing factors» that trigger the disease. Examples of such factors include divorce of parents, military service, or a sentimental break-up.

The use of psychedelics, understood as a stressor,  can also trigger schizophrenia. But only happens in susceptible, pre-morbid individuals. It is worth noting that the use of cannabis has increased worldwide in the past 20 years. Nevertheless, ºthe incidence of schizophrenia remains stable at around 1%.

In this sense, a family history of schizophrenia is an accepted risk factor for developing the disease. Your risk of developing schizophrenia may be higher than that of other individuals, but it does not necessarily mean that you will definitely develop the disease. So, many factors come into play, including age, personality, and previous responses to other drugs. For individuals with a family history of schizophrenia, the use of psychedelics is not recommended as a general rule.