I just dug out a paper I printed out a few months ago from the BBC. It seems that there is a chemical called cotinine that is a by product of nicotine and this helps with Alzheimer's, Parkinson's, and has antipsychotic properties. I'll try to put a link in case you are interested.
I'm amazed that a doctor would tell someone to smoke! I hope the other doctors don't find out about it - he's going to be very unpopular.