Why?
She has said nothing about this man thats bad.
He used to smoke weed every day but it made him paranoid and he stopped - that is not bad because when he had a problem he addressed it and stopped.
He has taken LSD. He hasn't lied to her about it he has told her about it. LSD is not addictive and is an intense experience. It is extremely unlikely he is going to start taking this drug problematically.
Many people have positive life improving / changing experiences from having experienced a strong haluncinogen but even if he hasn't experienced it like this and it is just a thing he has experienced, it is a life experience, that as long as he is sensible about it, wont impact him negatively and therefore wont impact her negatively.
Sure there are some risks, with a strong hallucinogen the risks are mental health related but harm is pretty rare with these drugs especially if people are sensible with company place and setting. There are risks to many parts of life.
Honestly there are a lot of judgemental and likely very hypocritical comments here (because the changes of everyone saying to leave him are drug free is slim, are you all tee total and never have a drink?) that are pretty ignorant regarding what he has taken and risks to the OP.
I cant imagine being in a relationship and thinking i had a right to dictate to another what they can and cant do with their body when they are away from me when that thing does not impact me. He is not cheating on her and risking her health. He is not deceiving and lying. He is not abusing her emotionally, physically or mentally. You are all talking as if hes disclosed he's been taking crack cocaine and he is about to start stealing her finances and self distructing his life or taking drugs around his kids because he has tried LSD with some friends and had a psychedelic experience. It is really ridiculous