Many people experience back aches during or after an acid trip. This is the basis of the infamous myth that LSD stays in your spine and causes flashbacks. Pure LSD will, in fact, not cause this phenomenon. The back aches are caused by the vascular-constrictive (constricting of blood vessels) properties of the various other amides of lysergic acid that will undoubtably be found in street acid. LSD is nearly impossible to synthesize and it is also nearly impossible to obtain pure ergotamine tartarate, from which LSD is made. Furthermore it is a very fragile molecule. It can be broken down by light or in the presence of strong acids or bases. This happens when a water solution of LSD crystals is futher dilluted by a dope peddeler with chlorinated tap water or applied to treated "blotter" paper. Some of the amides that it breaks down into are still psychoactive (although not to the same degree) but they have been blamed for many of the side effects.