I don't always say this, but I'd do what the doctor says in this case. It's not worth the risk, and who knows, they may know what they are doing.
The other factor is if you do have any problems and you're taking medication the doctor told you not to will that affect you insurance? Even if it's completely unrelated I'd expect the insurance company to try to get out of paying for anything and everything. You'd also probably lose any legal ability to go after the doctor if you had problems.