I read a great book in the early 80's, the basic premise is that an experimental drug allows peoples consciousness to time travel, I thought it was E van Vogt but it seems not, different coloured pills allow different effects.
closed as unclear what you're asking by user56, DVK-on-Ahch-To, The Fallen, phantom42, Ward Oct 9 '13 at 5:26
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It sounds a bit like Now Wait For Last Year by Philip K. Dick, though I'd guess this isn't the book you're thinking of because in Dick's book there aren't different coloured pills and the book isn't principally about time travel. Still, I thought I'd mention it just in case (and also to encourage people to read Dick's book :-).
Or possibly Cryptozoic! by Brian Aldiss. I don't have a copy of this book, but the description on Wikipedia sounds plausible.
Philip K. Dick's Ubik (1969) is another possibility. Drugs and time travel are involved, but the late 60's and early 70's are too hazy for me to remember anything about the color of the pills.