Probably the biggest no-brainer on this list is the use of anabolic steroids; it's how the cast of Jersey Shore was able to drink copious amounts of alcohol and still maintain giant biceps and six-pack abs. Technically termed "anabolic agents" in the WADA guide, steroids are the synthetic form of the male hormone testosterone, and can help you get jacked. Quick.
"Steroids increase muscle mass, strength, endurance, recovery time, and they essentially signal growth in muscle, and growth in everything that feeds energy," says David M. Ferguson, PhD, and professor of medicinal chemistry at the University of Minnesota. "You can watch someone struggle to bench press 200lbs, and [in] two or three weeks they're benching 400lbs, and it's all from the anabolic steroids... everything just goes to excess on steroids."
Athletes usually cycle on and off of them, especially during training when steroid use is the most beneficial for athletic gains. While they can be tested for them at any time, it's not uncommon for athletes to stop taking steroids a few weeks before competition and still test clean. Not that anyone would ever do that...
Human growth hormones (HGH) are usually mentioned along with steroids, and can increase muscle mass, bone density, strength, and even aid in recovery. But unlike steroids, which yield results pretty quickly, HGH must be taken over longer periods of time to reap the rewards, and aren't as common among Olympic athletes. Same with hormone and metabolic modulators, which are more rare but are used to help treat the side effects of using anabolic steroids, and can mess with hormone production.
Beta-2 agonists are lifesavers for athletes with asthma. Literally. When inhaled, they help dilate the blood vessels and relax the muscles surrounding the lungs, allowing them to breathe. They're allowed by the WADA, so long as the athlete has an approved therapeutic use exception (TUE) for them. But they won't do a non-asthmatic athlete much good in terms of performance anyway; beta-2s only have performance benefits when they're taken orally or injected, Dr. Ferguson says, and both forms are banned.
On the testing side of things, diuretics and other masking agents totally mess with the urine samples, which is kind of the point, but also why they're called out by the WADA. There's no other reason for healthy Olympic athletes to have a diuretic in their systems other than to dilute their pee.