I've taken LSD roughly a dozen times over the last 5 years give-or-take, and I'm not joking. I will admit that I embellished a couple of details because I was remembering rather than citing. Technically, no, it is not possible to overdose on LSD, but I think everyone who has taken it can attest that bad trips can and do happen sometimes, and it has the potential to be truly traumatizing. Annecdotally, I've certainly had my fair share of bad trips... Going back to Miller, here's an article going over some of the allegations in question. Admittedly, there is a lot of he-said-she-said, but just going off of the facts, Erza developed a close relationship with a minor 11 years younger than him, and allegedly gave them access to drugs and alcohol (LSD included), took away their ability to communicate with others (their parents), and "took control" over their personal possessions (i.e. ID and passport). The parents are the ones who claim their child suffered from a "days-long bad trip" just fyi. While Ezra and the (now) young adult deny it being sexual in nature... it has been described by many third-party witnesses as "extremely uncomfortable" and "basically a mini R. Kelly situation"