Surely, that's dosage dependent and frequency dependent. One per week vs once every three months vs once per year. Low dose vs medium dose vs high dose.

Plus, these things are illegal which means that most of the time you are not getting the real but instead pharmacologically similar substances that might have secondary effects. This is way you can't reliably imply a correlation because it is a black market and often what you think you consumed is not what you actually consumed.

Unless you actually tested what your friends consumed, you don't know what it was.