I don't think he just "sampled drugs", but rather probably used them for an extended period of time. That doesn't necessarily mean any long-term mental health consequences. Normally it may be actually the opposite, i.e., being a regular drug user, especially beyond your high school/unversity years , is a symptom of a preexisting mental health condition, rather than the drugs inducing that condition.
Regardless of drug use, what caught my attention, as I said before, is that Harry appears to have been gaslighted in the sense that he has been manipulated into doubting his own memories or past experiences. That is clear for example when he says that he now realizes that happy moments that he thought he had with his family shooting birds were actually part of a "cult of death" built around "the blood of animals". Without discussing the morality (or lack thereof) of shooting or hunting animals, clearly that is an opinion that was planted in his psyche, either by a therapist, or Meghan, or both, and that is troubling to me.
I read somewhere that “ Re therapy Harry wrote in the memoir that his dad sent him to a real therapist and psychiatrist and they recommended medication which he refused”. I hope I’m not crossing a line here, has anyone seen such an info in a publication? If not, could I ask HRH Hermione to see if it’s true when she’ll be so nice to us to give us a review of the book, please?