Why do you think nobody has replied to your physical harmfull question that could possibly kill 'your friend '. This is a harm reduction/ prevention site with regards to drugs, illicit or prescription, and provides essential pre, and post Drug use information and how to deal with such matters.
Baking powder may mess with the blood gases and pH buffer of the blood given its alkaline nature..
This is indeed a Harm Reduction forum, we cannot encourage anyone to shoot up drugs that are cut - especially if not with an inert (neutral / innocent) cut!
Also sorry but this rather belongs in the Other Drugs forum, I will move this thread for you.