I'd highly recommend reading "Drugs without the hot air" as a relevant resource for better understanding the risk profile of different drugs.
One of the key papers which it talks about is the 2010 paper "Drug harms in the UK: a multicriteria decision analysis" which found that LSD and Mushrooms are low harm.
However, as many others have already mentioned, the specific experience and consequences of taking any drug will depend on dosage and the context in which the drug is taken. If John does ever end up taking any psychadelics, he will be much safer to start with a low dose, and to take them with someone sober present as a trip sitter.
It may be interesting to raise that the evidence for LSD microdosing having the claimed effects is looking less promising these days. https://www.nature.com/articles/d41586-022-02876-5 provides a good discussion and https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9731343/ is the key placebo controlled LSD micro dosing trial result which came out in 2022.