If you mean creatine, advil, caffine, multi vitimins, gatoraide, etc. you are correct. Weight lifting is an artifical performance enhancer.
Indeed, in the past, professional athletes may have indulged in steroids, etc., but nowadays it is extremely rare. There is constant random testing---in season and off. The penalties are draconian.
The only scenario where I could understand a pro-player taking illegal PED's is where he (she) knows he will be cut if he doesn't vastly improve his performance. Then he might risk the drugs cause if they catch him he'll be suspended or waived, but that's what was going to happen anyway if he didn't turn it around.
Other than those cases, I don't think either college or professional athletes take illegal PEDs.
There are a lot of performing enhancement drugs that are not "illegal" in terms of US law but will still get you suspended from your sport. In my old sport, if you drank too much coffee, you could test positive (caffeine); if you took an over-the-counter cold medicine, you could test positive. If you want to take anabolic steroids, you can totally do it and be totally legal about it and still get suspended.
Every professional athlete -- if they really want to succeed and at the professional level, that should be everyone -- should be looking at every possible way to boost their performance and gain an advantage. That includes weight training, brain training, lifestyle choices, and diet.
For athletes with as much money as these guys have, they should exploring every avenue to boost their performance and that means exploring drugs and compounds that border on legality, drugs and compounds that can't be tested for, and methods to take drugs so that they won't show up on tests.
I imagine, and I could be wrong about this, but there should be designer versions of many of these drugs that don't show up on tests but give benefits. I imagine, and I could be wrong about this, that athletes are on protocols of compounds that the lay public hasn't heard of, yet, and that the NFL doesn't even know it needs to test for, yet. When testing for anabolics, they don't test for the drug itself, or even for having unusually high levels of testosterone, they test for its effect on the testosterone/epi-testosterone ratio and one of the things BALCO was doing was giving people a combination of drugs that maintained the test/epitest ratio so it didn't test positive.
For me, the concept of "performance enhancing drug" is problematic because there are some drugs that should be considered performance enhancing that are allowed... painkillers. And those are allowed in a lot of cases. If the NFL wants these guys to go out there without being chemically supported, then they shouldn't allow guys to get painkillers (or any other kind of injection) on the sidelines or in the locker rooms.