Peter Halsten Thorkelson (born February 13, 1942), better known as Peter Tork, is an American musician and actor, best known for a member of "The Monkees".

photo right from about 1966

In 1980/81 Tork is rpeorted to have given up alcohol and drugs, which might be part of his move to a generally healthiuer lifestyle, but we have nothing specific.

from biography on imdb.com :

Declined an invitation to rejoin The Monkees for a McDonald's TV commercial, as he is a vegetarian.

from www.syl.com :

One of the vivid representatives of vegetarian musicians is Peter Tork, the member of the Monkees band. The most important print left by in the history of vegetarianism was big protest action against the Mc Donald?s industry that was accepted and supported by most of vegetarian musicians.

from www15.brinkster.com :

Things He Hates: Hate, meat (Note: he's a vegetarian),

Official website http://www.petertork.com