The late writer Jules Siegel had enjoyed a particularly close relationship to the reclusive Thomas Pynchon, and much of what is thought to be known about the latter comes from the former’s interview with and observations of the author of Gravity’s Rainbow.  How much, or how little influence drugs, particularly hallucigenic drugs like lysergic acid diethylamide, LSD, had on Pynchon’s narrative is unknown.  If Siegel, however, is to be believed, and he should be despite any resentment he felt regarding Pynchon’s affair with his wife, then the writing of Gravity’s Rainbow was heavily influenced by drugs.  In Pynchon’s most famous quote regarding this particular novel, which is notoriously difficult to interpret, he is alleged to have told Siegel,

“I was so fucked up while I was writing it . . . than now I go back over some of those sequences and I can’t figure out what I could have meant.”

A 2003 article in the British newspaper The Guardian titled “Have You Seen This Man” about a documentary on the reclusive author noted the following:

“One writer, Jules Siegel, tells how his wife ran off with Pynchon in the 1960s, and alleges, bizarrely, that Pynchon was involved with the US government's LSD experiments on unwitting subjects. Others tell anecdotes of Pynchon haunting bookshops in disguise, or turning up incognito at Pynchon-lookalike parties. The man himself, of course, is nowhere to be seen.” http://www.theguardian.com/film/2003/may/05/artsfeatures.fiction

That it has become a given that Pynchon indulged from time to time in hallucinogenic drugs is evident in the popular mythology that has grown up around the author, who is still alive.  A 1994 article by Andrew Gordon had this to say about the times in which Pynchon was most active and about the pervasive influence of drugs:

“I returned to a different country than the one I had left four months earlier. The first teach-in on the War had been held at Rutgers that spring. The number-one tune was no longer the Beatles' sweet chant, "I Want to Hold Your Hand"; now people were listening instead to the angry, insistent lament of the Rolling Stones, "I Can't Get No Satisfaction." A chemistry major told me about his experiences with a new wonder drug called LSD. He said he had found nirvana and met God. I thought, if it could do that for this schnook, then what could it do for me? I ingested 250 micrograms and wound up in the hospital.” [“Smoking Dope with Thomas Pynchon: A Sixties Memoir,” http://web.clas.ufl.edu/users/agordon/pynchon.htm]

Gravity’s Rainbow is about the search during the final days of World War II and in the immediate post-war period by American, British and Russian agents for the German scientists behind the development of that country’s sophisticated and exceedingly threatening ballistic missile program.  Such searches did, in fact, occur, with the rush by the “Allies” to locate and appropriate as much of the German rocket program and the scientists behind it as humanly possible.  Whether this missions was surrealistic or not, one can be forgiven for suggesting that Pynchon’s interpretation of it was heavily influenced by drugs.  Read the following passage and, in the context of the novel’s plot, determine for oneself whether the author was experimenting with LSD or with any other mind-altering substances:

“Now there grows among all the rooms, replacing the night’s old smoke, alcohol and sweat, the fragile, musaceous odor of Breakfast: flowery, permeating, surprising, more than the color of winter sunlight, taking over not so much through any brute pungency or volume as by the high intricacy to the weaving of its molecules, sharing the conjuror’s secret by which—though it is not often Death is told so clearly to fuck off—the living genetic chains prove even labyrinthine enough to preserve some human face down ten or twenty generations . . . so the same assertion-through-structure allows this war morning’s banana fragrance to meander, repossess, prevail. Is there any reason not to open every window, and let the kind scent blanket all Chelsea? As a spell, against falling objects. . . .”

At the end of the day, the best evidence that drugs played a role in Pynchon’s vision comes from the quote above recorded by Jules Siegel.  Personally, I’ll take Siegel at his word that the quote was fairly and accurately reported.