My wife is 56 years old, fit and active. A year ago she wouldn't even take a pill for a headache.?

No, you were right to state what you did. If a situation degrades down that you need to issue an ultimatum like that one - it's pretty acceptable. (For the readers: please note that his wife is taking drugs - if it was a matter of choosing between him and her friends, that's an entirely different matter.) She's putting crap in her body and for what? To do better athletically? I hate making suggestions like this but maybe she has a mental image problem. Anorexics always feel they look fat and will keep going and going if people let them. Your wife will probably continue to do so if she goes unchecked. I think it's time you informed her doctor and tell her that she needs to seek help.

I'd seek counseling together, find out the safety of what she's taking, the reason(s) for her new obsession with these enhancing products (if she's not a competitive athlete, what's the point???) and the chances it could be harmful and/or lead to things that are harmful...

Many people who smoke pot, don't move on to harder drugs...so, one could also assume someone who injects safe/legal products to enhance their fitness or performance, may not ever move on to the 'hard stuff'...