The attribution of the poisoning to the CIA in Albarelli's book has been roundly criticized. Historian Steven Kaplan, author of an earlier book about the events, said that this would be "clinically incoherent: LSD takes effects in just a few hours, whereas the inhabitants showed symptoms only after 36 hours or more. Furthermore, LSD does not cause the digestive ailments or the vegetative effects described by the townspeople."
To be clear: I have no reason to believe that the CIA circa 1951 wouldn't or couldn't pull this kind of stunt, just that the evidence that they in fact did is pretty shaky.