On the issue of strychnine in LSD:

The following text was written by Alexander T. Shulgin in response to the overwhelming misconception that strychnine is commonly found in street samples of LSD:

"The observation of strychnine as being present in any street drug, as a by-product, or a contaminant, or an impurity has never been documented.  It is a natural plant product, as are the ergots which are used in the synthesis of LSD.  But they come from totally unrelated plants;  there has never been a report of strychnine and an ergot alkaloid co-existing in a single species.  So if the two materials are together in a drug sample, it could only be by the hand of man.  I have personally looked a large number of illicit street offerings and have never detected the presence of strychnine.  The few times that I have indeed found it present, have been in legal exhibits where it usually occurred in admixture with brucine (also from the plant nux-vomica) in criminal cases involving attempted or successful poisoning.

The same argument applies to the myth that occasionally surfaces, that strychnine occurs in the white tufts of peyote.  This is equally fraudulent -- it has never been reported in that cactus or any other cactus."

Furthermore, it should probably be spelled out that strychnine is not needed to bond LSD to blotter paper, nor is strychnine a breakdown product of LSD.  these are probably the two most commonly repeated gross misconceptions.

The source of the "strychnine is commonly found in LSD" myth may be somewhat grounded in truth.  For example, in "LSD: My Problem Child" Albert Hoffman cites a case in the late sixties of Strychnine being found in an "LSD" sample that was a white powder.  However, what is commonly claimed is that strychnine is found in a significant percentageof LSD, specifically blotter LSD, which is *not* true.  Shulgin's note that he has analyzed many samples of LSD and never found strychnine is backed up by published analyses done by PharmChem and the LA County Street Drug Analysis program, which likewise never found any strychnine.
 
This is intuitively backed up by the fact that a 5mm x 5mm "standard" square of blotter LSD only weights about 2mg and if the paper itself was made completely out of pure strychnine it is still on the very low end of Strychnine's threshold of activity.Strychnine is not the cause of tracers, cramps, nausea, or amphetamine-like LSD-effects.  Its possible that poorly synthesized LSD might have other ergot derivatives in it, which might contribute to the harsh body load that some get on taking LSD.  Also, the very close chemical relatives 1-Methyl-LSD and 1-Acetyl-LSD (which break down into LSD in aqueous solution) might be present in some street samples and might contribute to the harsh body load.  (Petter Stafford has claimed in his _Psychedelics Encyclopedia_ that 1-Acetyl-LSD is supposedly "smoother" than d-LSD -- thus "strychnine laced acid" may acutally be pure d-LSD, while "pure lsd" may be 1-Acetyl-LSD or some substitute).  And the chemicals iso-LSD and lumi-LSD which are breakdown products of LSD might contribute to the body loading on some trips, particularly via a hypothetical synergistic effect.  Given this plethora of possible chemicals in street "LSD", its not needed to look to a chemical which has hardly ever been found in analyzed samples to explain variations in the strength and "cleanliness" of street acid.
 
Its also possible that LSD itself simply causes adverse physical effects, particularly muscle cramping, in persons suceptible to it. The reported side effects of LSD (the nausea and apparent CNS stimulant effects) are commonly reported side effects of seritonergic drugs such as fluoxetine (Prozac) and buspirone (Buspar), and also are commonly reported (and typically more severe) with other psychedelics like Mescaline.

Or its quite likely that the "strychnine" reactions to LSD are entirely psychosomatic.  Both Leary ("The Psychedelic Experience") and Lilly ("Programming and Metaprogramming...", "Center of the Cyclone") have each observed this reaction in people who cannot handle the surge of emotion associated with a trip.
 
Further advice would be to avoid methylxanthines (caffiene, theophylline in tea, etc) prior to dosing.  Some have noted a possible synergistic effect between them and LSD causing, or contributing, to a harsh body load during a trip.  And prior use of dramamine may alleviate the nausea sometimes associated with LSD, and other psychedelic drugs (although it may also effect the quality of the trip -- Shulgin has noted in PiHKAL that he shuns the use of anti-nauseants in order to experience the effects of the psychedelic, both good and bad, with no possible interference).

In summary, it can't be said that we know specifically why sometimes acid feels "cleaner" than other times.  However, based on the availability of plausible explanations, and the evidence of drug analysis, and general implausiblity of the whole strychnine concept, we can conclude that it isn't due to any concentration of strychnine.  Also, while it can't completely be ruled out, the presence of strychnine in LSD is so minimal that the majority of LSD users will never once come across it.