[Shaun]

Originally Posted by Graham

Err, I suggest you do a little research into the drugs that are *already* used for medicinal purposes!

For example:

Morphine is an opiate (derived from the same source as heroin)

http://www.bartleby.com/59/22/morphine.html

Novacaine is chemically very similar to cocaine (but less toxic)

http://www.fas.org/news/reference/probert/E2.HTM

Interestingly they are alkaloids, like codeine and strychnine, all have similar functional groups (an amine group).

Another chemical you may have all tried at some point is quinine, found in tonic water, this is also chemically similar but doesn't affect your mental state.