First off, in theory we're all talking about the drug known as 9,10-Didehydro-N,N-diethyl-6-methylergoline-8�-carboxamide , commonly referred to as LSD, D-Lysergic Acid Diethylamide, Acid, etc. I mention this because whenever we're dealing with illicit substances, it's important to remember that unless you have a proven scientific method of identifying the substance, you really can't be sure.
I don't think I'd be wrong in assuming that a majority of those that have used LSD repeatedly have probably used other drugs as well. Was LSD the only drug this person had ever done? Can you verify that the substance in question was actually LSD? (The word of a drug dealer doesn't count, and personal testimony based on taking a sample from the same batch isn't concrete proof, since there are a variety of hallucinogenic drugs with similar effects. From personal experience with a variety of hallucinogens, I will attest that it is not possible to identify psychelic substances by taking them. LSD is an incredibly complex and unstable molecule. It's very difficult to produce, high in demand, and there's a handful of related drugs with virtually indistinguishable effects. I challenge anyone to take an unknown hallucinogen and tell me they know for a fact whether it's LSD, 2C-I, 2C-T-7, LSA, ALD-52, or any number of other drugs. They all exhibit similar effects in varying proportions, with less consistency than other types of drugs. The same dose from the same batch of the same drug can produce a wide range of experiences depending on things like setting, emotional state, physical condition, etc. 2 hits of acid might feel great if you're going to sit out in the sun and watch the clouds, but the experience won't even be recognizable if you swallow em right when the cops pull you over. So once again, can you verify that it was indeed the drug in question that caused your friend's brain damage? If so, what's the dosage? How many times? How much time in between uses? There's a lot of variables to consider.
What about family history of neurological disorders? What about physical injuries? What about psychological trauma? We're talking about an entire lifetime full of potentially brain damaging incidents. How can you blame brain damage on LSD when there's a bunch of other possible causes, and no proven method for ruling all of them out? Not to mention that even when we understand the way drugs interact with the brain, there's not nearly as much information on combinations of drugs, cumulative effects of regular use of different substances, by people of different ages or genders, etc. There's so many variables to consider before pointing to LSD as the direct cause of brain damage, neurological disorders, etc.
I'm not saying LSD is without risk, or that I know for a fact that it can't cause brain damage. But so far, I've yet to see any proof that use of LSD causes brain damage. And even if it hypothetically could cause brain damage, there's still the question of circumstances. Even if LSD has the potential to cause brain damage, does that mean everyone who tries it is at risk? How much or how often before damage occurs? Does it only happen to people with certain pre-existing conditions?
Any responses? Does anyone know of documented cases of brain damage where all the aforementioned possibilities have been ruled out, and the cause has been identified beyond a reasonable doubt as LSD?