Bodybuilders often take a powdered form of protein, the essential building blocks for muscles, as a supplement as it is necessary to consume large quantities and protein shakes are convenient. The most commonly consumed type is whey protein since it is a naturally complete protein and is a rich source of branched chain amino acids (BCAAs), containing the highest known levels of any natural food source. It is also very quickly absorbed by the body and metabolized.

     Casein is the richest in glutamine, and has casomorphins which help release aminos over a long time. Soy protein is also naturally complete and also contains isoflavones. Many people also will use egg (white) protein, as it is a lactose- and dairy-free complete protein. Protein powder is generally consumed immediately after exercising, or in place of a meal.

Glutamine

     Glutamine is the most abundant amino acid found in human muscle and is supplemented as supplement manufacturers claim the body's natural glutamine levels are depleted during anaerobic exercise and therefore may cause a deficiency. Glutamine is not an essential amino acid which means the body can naturally replenish its own stores. It is argued that supplementation by bodybuilders may still be required as deficiency may lead to a weakened immune system and wasting of muscle tissue. Many bodybuilders supplement with glutamine. It plays a vital role in protein synthesis. It is sold as a micronized, instantly soluble powder.

Branch chain amino acids

     Amino acids are the building blocks for protein – the body breaks consumed protein into these in the stomach and intestines. There are three branch chain amino acids (BCAAs); each has numerous benefits on various biological processes in the body. For more information on this visit the articles on each of the specific aminos: leucine, isoleucine, and valine.

Meal Replacement Products (MRPs)

     Meal Replacements Products (MRPs) are either pre-packaged powdered drink mixes that you mix with water, milk, or juice and then drink; or bars that you eat. Both are consumed in the place of a whole-food meal. Generally MRPs are high in protein, low in fat, have a low to moderate amounts of carbohydrates, and contain a wide array of vitamins and minerals.

     The majority of MRPs use whey protein, calcium caseinate or micellar casein, soy protein and egg albumin as the protein source. Carbohydrates are typically derived from maltodextrin, oat fiber, brown rice, or wheat flour. Some also contain flax oil powder as a source of essential fatty acids (EFAs).

     MRPs can also contain other ingredients that are deemed beneficial to bodybuilders. These can include, but are not limited to creatine monohydrate, glutamine peptides, l-glutamine, calcium alpha-ketoglutarate, additional amino acids, lactoferrin, conjugated linoleic acid (CLA), and medium chain triglycerides (MCT).

Prohormones

     Prohormones are precursors to hormones - and were most typically sold to bodybuilders as a precursor to the natural hormone testosterone. This conversion requires naturally occurring enzymes in the body. Side effects are not uncommon, as prohormones can also convert further into to DHT and estrogen. To date most prohormone products have not been thoroughly studied, and the health effects of prolonged use are unknown. Although initally available over the counter, in 2004 their purchase was made illegal without a prescription in the US, as it now is in almost all countries and sporting bodies.

Creatine

     Creatine monohydrate is an organic acid naturally occurring in the body that supplies energy to muscle cells for short burst of energy (such as lifting weights) via creatine phosphate replenishment of ATP. A number of scientific studies have proven that creatine can increase strength, energy, and muscle mass in addition to reducing recovery time. Also, recent studies have shown that creatine improves brain function, improves recognition memory, and reduces mental fatigue. It increases what is known as cell volumnization as it draws water into muscle cells, making them larger.

     This intracellular retention should not be confused with the common myth that creatine causes water retention (or intercellular water retention).

Thermogenic Products

     Thermogenics is a broad term for any supplement that the manufacturer claims will cause thermogenesis – resulting in an increased metabolic rate, increased body temperature and consequently (the promise of) an increased rate in the burning of bodyfat. Until recently almost every product found in this supplement category was comprised of the "ECA stack": ephedrine, caffeine and aspirin (however these were normally found in their herbal form of Ma Huang, Kola nut or Guarana, and white willow bark, respectively). However, on February 6, 2004 the FDA banned the sale of ephedrine and its alkaloids and manufacturers were forced to look for alternatives. Nowadays, the "ECA" stack is more likely comprised of bitter orange or Citrus aurantium (containing synephrine) instead of the ephedrine. To date the effectiveness of this new combination is far from conclusive.

Testosterone Boosters

     There are several naturally-occurring plants and vitamins as well as synthetic chemicals that supplement companies claim may produce an increase in testosterone levels. However, the validity of many of these products is questionable due to a lack of valid scientific research showing their effectiveness at this time. The most commonly taken supplements of this type are ZMA and Tribulus terrestris.

     A relatively new drug/supplement marketed as 6-OXO is gaining popularity as a testosterone booster.

Nitric Oxide Stimulators

     Many studies show that nitric oxide (NO) acts as a signaling molecule that plays a vital role in causing the relaxation of the smooth muscle tissue that makes up the walls of blood vessels. NO freely crosses the endothelial cell membrane into the smooth muscle tissue of the blood vessels to facilitate vasodilation. Promoters argue this allows more blood and oxygen, and hence more nutrients to be delivered to muscle tissue, while increasing waste removal – aiding muscle growth. This is called active hyperemia. However, NO supplements do not actually contain nitric oxide but the amino acid arginine and other precursors such as citrulline, Pycnogenol, L-aspartic acid, and ginsenosides – which the body uses to synthesize NO.

-Wikipedia.com