Hey moron, shut up. LSD is not a bad idea. LSD, is illegal because it is too useful. Did you know there were studies done in the fifties about LSD as a painkiller, stress reliever etc. Did you know they never released the results to anyone? Do you know why? NO, you don't. Because the usefulness of LSD was too good to be true. It proved to have painkilling effects up to a week after being dosed at a SUB psychedelic amount. On top of all that LSD is one of the most safe chemicals known to man *physically not psychoactive* and is less neuro-toxic than vitamin C or E.
Flashbacks= A lie. There is no such thing as a flashback that will just suddenly occur. HPPD is what a "flashback" is. Hallucinogenic Perceptual Persistence Disorder. HPPD will be noticed after coming down from a trip, or waking up the next day in most cases. No, it will not make you think that the world is going to end. You may see things in the corner of your eye that aren't truly there. Or there may be some patterns in the lawn (awsome).
Now that this ignorance has been dealt with. To the OP.
DXM is fun, not the best thing for your liver. No worse than drinking though. Look at the bottle that your roommate drank. You should not take any cough syrup that contains any other active ingredient than Dextromethorphan Hbr or Hcl. DXM Hbr is the extended release. Meaning smoother trip, less intense and longer. My best guess is that your roommate is an idiot and drank some syrup with guaifenesin in it. Guafenesin is an expectorant A.K.A. makes you puke.
I have no more to say, except this.
/endthread