Grapefruit adversely affects the metabolism of MANY drugs by inhibiting the cytochrome p450 pathway. I'm not sure about LSD specifically. But if I were going to take ecstasy/Molly, mescaline, or any other drug made from the a  5e31  mphetamine backbone, I would stay the fuck away from grapefruit or pomelos. Other citrus fruits are fine. https://en.m.wikipedia.org/wiki/Grapefruit%E2%80%93drug_interactions