I first heard this song as recorded by the great Jim Kweskin Jug Band; it was the title cut of one of their albums:

http://www.amazon.com/Relax-Your-Mind-Jim-Kweskin/dp/B0000C509U

What a wonderful ensemble, but prehaps not as well-remembered as they should be. Those of you younger than 60 or so, as well as those not living in the US during the 60s: if you haven't given a listen to this band, do yourselves a favor...