Erowid is a pretty good source of info on drug use experiences: https://erowid.org/chemicals/lsd/lsd_faq.shtml
It mentions that niacin (B3) and vitamin C are both reported as helping with after-effects from LSD, and tomato juice contains both. Hydration and salt replacement probably won't hurt, either.
(I think the strychnine thing is a myth, in the same sort of vein as razorblades in Halloween apples? I'm not aware of any reason why either LSD or psilocybin would contain it; mushrooms certainly can contain lethal alkaloids but AFAIK strychnine isn't among them.)