Acid.

Several urban legends claim that intermittent flashbacks are the result of trace amounts of LSD or related chemicals being dislodged and released into the body after having been crystallized and stored in fat or spinal fluid cells. However, there is no evidence for this and scientific research suggests that it is not the case; LSD (which is water soluble) is metabolized in the liver, as with many other drugs, and its metabolites are excreted normally in the urine

You have to realise that screen writers aren't sceintsts they simply write what they have heard/know for the most part. This belief was taught in scools in the 70's and 80's and began from the notion of flash backs and from observations that The drug experience sometimes spurs long-term or even permanent changes in a user's personality and life perspective.

While there is no proof that LSD stays in your system there is proof that taking it can have a pro-longed effect on a person for years after taking the drug.

Not really SPOILERS below, but more at the LSD trip the author of the script took in the 60's.

Actually the movie is autobiographical of the enormous hit and subsequent trip and madness the writer, James Toback, experienced in the late 60's, after [allegedly] taking the largest recorded hit of approximately 100,000 micrograms, and living through it. It began with 9 hours of bliss. A friend from Arizona shattered his state of bliss, when James asked how long his trip was supposed to last, the friend stated, "Sometimes it never ends." which shattered James' state of bliss in an instant. What followed was 8 days of indescribable catastrophe — physically, emotionally, and every other way.

In this movie "Harvard Man" [Chapter 16 on DVD titled "15,000 micrograms"], the character Alan Jensen, had taken 15,000 micrograms (188 to 750 modern doses); this is slightly over the toxic estimate.

In the sixties a hit was 200 to 1000 micrograms, 100,000 micrograms is therefore around 10 to 50 hits in the case of James Toback. Appears a 1960's formulation is the same as the modern formulation as far as Wikipedia goes, near top speaks of dosing strengths.

http://www.harvardindependent.com/ViewArticle.aspx?ArticleID=9822

http://en.wikipedia.org/wiki/Lsd

http://www.everything2.com/index.pl?node_id=1433919

The toxic quantity is currently estimated at 14,000 micrograms of LSD-25 from below link (a single dose today is from 20 to 80 micrograms), but above 100,000 microgram dosing is of an earlier era wherein 200 to 1000 micrograms was a dose; so currently a toxic amount is estimated at 175 to 700 doses (the lower the dose the better the trip, probably why the dose is smaller now). Still, if this is the same drug (strength as is usually administered in a dry form), James Toback took 1250 to 5000 modern doses, over 7 times the toxic estimate. Very very lucky that an antidote was administered by Max Rinkel, the researcher from Boston Psychopathic who first brought LSD to the States.

http://www.emedicine.com/ped/topic2809.htm

It's hard to say which is more ignorant about acid; the things said and shown in the movie, or some of the things being said on this thread. I'll deal with the movie first. The psych prof says essentially that everyone who took acid in the sixties is either meditating in Nepal, or in a psych facility. Of course, that is nonsense; most of us who took acid back in the day simply moved on to other phases of our lives. After all, acid isn't really a "lifetime use" drug, such as marijuana or alcohol. Secondly, the amounts discussed in the movie are ridiculous. If that chem major did such a great job researching Sandoz acid, she would have known that a typical dose was 100 mics, with 500 being enough for an extreme trip. Why the hell would she put 5000 mics on each sugar cube, and then give three such heavy overdoses to one friend? Of course, after taking all 15,000 mics at once, on an airplane no less, the character would be in for an extremely long, extremely bad trip. However, both the visual and aural effects portrayed in the movie were in no way reminscent of the actual LSD experience. Faces were more likely to turn paisley then distort the way they were shown, and where were the echo effects on his hearing? Most important, where was the sh!t eatiing grin that was always plastered on the face of people tripping on real acid, regardless of whether the trip was bad or good? The director may have taken acid once himself; it doesn't appear that he ever observed others in that state.

Now, as to a couple of comments here on the board; one, that acid doesn't last forever, and two, that flashbacks are an urban legend. Both ignore what LSD-25 was originally developed for, to simulate pychosis, specifically schizophrenia, in test subjects, for study purposes. If a person takes LSD who is already biochemically prone to schizophrenia, the drug can precipitate a full blown case, which can last a lifetime. You see, there actually are people who've been in mental health facilities for decades after using acid. It's relatively rare, but can happen. Flashbacks also do happen, but they're not caused by deposits of the drug in the body. It's a more complicated, mental reaction. The proximate cause could be use of another drug, especially some of the more potent strains of marijuana, or some incident that recalls an experience while under the direct influence of acid. One of the semi-accurate things said about acid, is that some effects can last long after the use of the drug. Specifically, the insights gained through what we might call a "meditative" use of acid, as oppposed to simple thrill seeking, might have a profound and lasting effect on someone's understanding of self, and how they relate to others.

In some rare occations it does last forever... sad but true. If u rule out those individuals who "last forever" by oblivionate themselves by the means of suicide (aka kill themselves under the influence of LCD...), there are still some people living today under the diagnosis schitzophrenia, which were triggered by the drug when taken in the late 60's.
I have myself during my psych studies encountered 3 patients whom still, after over 30 years (early 70's), have not been recovered from their trip.
The happy news is that some of these poor souls are still alive, so there might still be a chance that one of them will get well before dying of old age at 84.
So i guess this would be the 2nd most stupidest goddamn thing you've ever heard;)

Went to Harvard myself, so i won't bother telling u all the real stupid things about the movie you'd annoy yourself with:) - like why he'd be running into one of the libraries when in the next scene it's supposed to be at the dorm...

In my own way, I am king. -Hail to the king, baby!

actually it is widley accepted that people that are genetically predisposed to mental illness can have said mental illnes triggered by constantly taking softer drugs for even just a month or two or taking harder drugs (which would include acid) just once. flash backs are also common to people both people who do suffer from mental illness and those who dont. this has nothing to do with acid remaining in your system, it is more to do with the damage it causes your brain. it is called hallucinogen persisting perception disorder or HPPD. over 30 percent of LSD users claim to have had "flashed backs". a higher proportion of psychiatric patients report flashbacks than "normal" users but i can't remember the actual percentage. it is not common for someone to enter a permenent state of psychosis from taking acid but it has happened alot of the time because of the amount taken by the user was far too much.

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I did a bunch of acid when I was younger. I tripped every single day for the entire month of December 2000. Hell of a good time. Haven't touched it since, although I did try some shrooms this past summer. They don't even begin to compare to a good acid trip, in case anyone was curious.

I get random flashbacks, but not very often. I think I've had maybe 10 in the past 9 years. Are they acid related? Who knows. I'm also bipolar so they could be from that, but they've never happened while I was manic so I kind of doubt it. I do hallucinate when I'm in a manic psychosis but it's nothing like the flashbacks.

ETA: I've been bipolar my entire life. Seriously. I started showing symptoms as a toddler but childhood bipolar wasn't widely known to exist at that time so nobody knew what was wrong with me. I was diagnosed with major depression in my early teens, put on Paxil, and went into a manic episode that lasted all through high school until I quit the Paxil. It was kind of fun. The acid did not trigger my bipolar disorder but it may have contributed the manic psychosis I started getting later on. I would go into the psychosis once in awhile as a teen but had mostly the "good" fun mania. Now when I don't catch the mania in time, I always go into a psychosis. That sucks.

I had a friend in college who had been taking so much acid that she had to take 10 hits at once in order to trip. Her body had built a tolerance to it. I had the same experience with mushrooms. I spent a month in Amsterdam doing them, and the highs get less and less each day. I'd have to do more and more to get the same high as the first night. If I went a week without doing them I'd get the same high on one gram(my initial dose). If I did it daily, I'd have to do several grams. I was never willing to experiment like this with acid, but I did watch my friend take up to 10 hits one night just to get the same high as the one hit the rest of us were doing.

I think the movie portrays the faces swirling during the hit in order to show the viewer what a trippy effect was like. I've never seen faces swirl, but I doubt that I could adequately show what I was seeing in a video. I remember one very tan girl looked like a human face carved into a piece of driftwood. So I think this was a good depiction, even if not so accurate. What I did find realistic was when Adrien Grenier was talking to the one girl in his dormroom and the character in the painting on the wall started moving. I've never had the image come out of the painting, but I've definitely seen images moving like that. I specifically recall a bunch of us staring at a dartboard and watching it spin so fast that its colors were swirling. Of course it wasn't spinning at all, but we all saw that. And when he was in the taxi with Eric Stoltz and everything coming out of his mouth sounded like gibberish at high speed. I've never spoken like that, but that's how other people sounded at times.

I don't know anyone who's ever had flashbacks from acid, and I know people who have done a ton of it. But I do know of people who's lives were ruined forever. One guy went to Cornell. He had to drop out, move back home and never really got his life together. And then there's the famous Syd Barrett of Pink Floyd. His was a combination of too much acid and undiagnosed mental disorders. It's thought that he probably would have lost his mind eventually, but acid brought it about at a much earlier age.