The nastiest drug I’ve yet heard of is PCP. Don’t take my word for it, look here: http://www.erowid.org/chemicals/pcp/pcp_info1.shtml
I’ve never heard reliable reports of any other drug producing trips that bad.
LSD can cause brain damage, or more specifically damage of neural pathway occupied by Serotonin. The neural pathway that Serotonin occupies was designed, so to speak, for Serotonin. LSD occupies this pathway hence imitating Serotonin. The LSD molecule actually burns these pathways (altering them). Occasional use will allow your brain to repair these pathways. But extreme use can leave permanent damage (scarring). I once took about 20 acid trips in a span of 2 months and had severe problems with flashbacks for 2 years. It is this altering of the pathways which I believe is the primary cause for flashbacks. It gets kinda complex to go deeper but I’m quite sure it is the real reason for flashbacks.
LSD is not stored in the body and is completely eliminated from the body 24 hours (or shorter) after ingesting (considering you don’t have liver problems).
I studied psychotropic drugs for a years when I was younger. I did research on them, and had first hand experiences with most of them (about 100 different mind altering/affecting drugs in all). Maybe that’s why I seem quite weird to some people. Actually, I’m surprised my brain even works now-a-days.
100 different drugs? Name 'em 
lessee, there’s benedryl, dramamine, lsd, marijuana, cocaine, lsa, psylocibin, psylocin, morphine, heroin, opium, pcp, freebase cocaine, bufotoxin, ketamine, dmt, jimsonweed, lithium salts, ritalin, dextromethorphan, booze, yage, kava kava, ug. too many drugs have ruined the momery. i mean memory. or do i?
that’s 23 for ya so far, Soli. damn!
I’m not sure what crackhead told you this, but…Bollocks!
Try gettin yer learn on someday, and come back when you understand what psychotrpoic drugs and hallucinogens do.
As stated by Silo, every time you come into contact with a drug as mind-altering as LSD(ever wonder why they call it Mind-altering?), your brain is essentially chemically re-mapped. Things change in your head every time. It might not affect you today, and maybe not even tomorrow, but you might find yourself down the road, 20 years later with severe Serotonin deficiency issues.
Ya wanna play with hallucinogens? try messing around with something a bit less malevolent, like Mushrooms. Out of all Hallucinogens, AFAIK, they do the least damage, and maybe close to nothing(I’m still the same ol GaWd I ever was :)).
And, no, the 3 hit Urban legend is just that, an Urban Legend…
-Sam
Who’s to say that the changes that occur in brain chemistry are bad? I feel that my experiences with psychedelics have led me to greater understanding of the universe – and have lessened my fear of the unknown. And besides, I believe that the chemicals I ingest unwittingly (car exhaust, factory exhaust, food preservatives and dyes, etc.) are at least as harmful, if not more harmful, than chemicals I ingest knowingly.
Lesseehere…
Knowingly ingest NaCN (sodium cyanide) or,
Unknowingly ingest NaCl (table salt)…
Hmmmm… 
Steve-O, you are way out of line. Did you think you could compare sodium cyanide to lsd and not get called on it? Do you realize what the LD50 of acid is?
and conversely, comparing smog and acid rain (no pun) to table salt?
Are you daft, boy?
Silo, interesting that you made the connection with LSD and serotonin. I used to drop acid quite a few years ago. Haven’t had any in 16 years now. But once a psychiatrist prescribed Paxil to me (it’s similar to Prozac). It’s a “serotonin reuptake inhibitor.” I used it a few times. I noticed an odd similarity to LSD. Not the trippy part, of course – there was nothing trippy about it. It was that edgy electric feeling that slightly sets your teeth on edge, the first signal that LSD is beginning to take effect before the trip begins.
GaWd: I’ve never noticed any signs of brain damage from the trips I have taken. Then again, some say I’ve always been crazy.
jrishaw: The last time I did LSD, about eight years ago, I was having – I guess flashes is the only appropriate word – flashes similar to the rush of amphetamines more than 18 hours after ingesting the acid. I appreciated this as I had to drive more than 360 miles that day and those flashes helped keep me alert.
Did I think that I wouldn’t get called on it?
Yes, that’s EXACTLY what I thought, because I figured that everyone would have realized that I was PLAYING with what Boots had written in the post just before mine. I was intentionally taking
“…I believe that the chemicals I ingest unwittingly… are at least as harmful, if not more harmful, than chemicals I ingest knowingly”
out of context, and taking the implications to an extreme for the purposes of having fun.
purpose… dag-nabbit
I never said you would crazy.
When you deal with people who use drugs enough, and step back from it and reflect(if you yourself are of sound mind), you realize that there are certain types of people who will become damaged, and those who will come out of it nearly unscathed.
My mom hung around with 2 girls in high school. They all did the same drugs, in the same quantities more or less, at the same time. One girl ended up a baglady in our town, one girl ended up in a Pacific Northwest mental institution, and one girl went to college and got several degrees, had children and led a life of normal mental capacity.
So, different people can do different things to their brains and come out of it differently. The brain is very fragile and we don’t yet understand wht we’re doing to it when we use chemicals like LSD and other drugs.
-Sam
This is the kind of question that’s really hard to answer.
First, many of the people who use it tend to use a bunch of other drugs too, so if someone goes nuts, who’s to say exactly which drug did it? And who’s to say it was the fault of any drug at all? Many researchers believe that, though it doesn’t cause insanity itself, LSD may bring underlying mental problems to the surface (i.e. the user was going to go crazy sooner or later. The acid just made it sooner).
And call me jaded, but I have a tough time swallowing any government-sponsored research after the way they tried to pull the wool over our eyes with the “work” of Gabriel Nahas. This man would suffocate moneys almost to the point of death with pot smoke, then record the effects as proof that pot was harmful. After being blasted by many medical journals, Nahas recanted all of his dozens of anti-pot studies as meaningless.
Research on Schedule 1 drugs is unbelievably biased in favor of the the drug warriors. To do research on these drugs, you need to have government approval. To get approval, the aim of your study must be to prove the harm of the drug. You must be actively trying to prove the drug will mess you up. Objective studies not allowed. Take a look at some of the results of drug research performed in the U.S. Now take a look at similar studies peformed overseas, most of which have results contradictory to the U.S. studies. We could believe that every study ever done in Europe was peformed by corrupt hippies who have a vested interest in the legalization of drugs, as the drug warriors would have you believe. Or we could believe that the drug warriors are full of sh*t.
FWIW, my wife once took a Psychology of Substance Abuse course at a major university. The professor told the class that LSD was practically harmless. YMMV, of course…
wow, i get that from Zoloft (another SSRI). that weird feeling of kinesthetic rising action. it kept me from getting asleep at night sometimes.