BGH stands for Bovine Growth Hormone, which is naturally produced by the pituitary gland of cows, and regulates their growth and metabolism.  BGH is the layperson’s term for what is known in the scientific community as Bovine Somatotropin, or BST.

The small "r" in front of BGH or BST stands for "recombinant", meaning that the BGH or BST is genetically engineered, and is therefore a synthetic version.  All milk contains naturally produced BGH, but rBGH can only be found in cows that have been injected with the synthetic version.

Yes, Posilac is Monsanto’s brand name for rBGH.  In 2008, Monsanto sold its artificial hormone business to Eli Lilly, one of the largest pharmaceutical companies in the world.

Dairy cows are injected with rBGH to increase their milk production, and subsequently increase profits.

Yes, the Food and Drug Administration approved the use of Prosilac in 1993 stating that the residue levels of this hormone in food has been demonstrated to be safe. However, critics point out that rBGH has not been properly tested in humans for long-term effects. In fact, rBGH has been banned in Canada, New Zealand, Australia, Japan, and all 25 members of the European Union because of the lack of evidence supporting the safety of rBGH for human health.

Milk from rBGH-treated cows contains higher levels of Insulin Growth Factor 1 (IGF-1), a hormone considered to be a high risk factor for breast, prostate, colon, lung, and other cancers. Cows given rBGH also experience higher rates of mastitis, a painful udder infection.  These cows are treated with antibiotics, which ultimately end up in the milk they produce, and facilitate the creation of antibiotic resistant bacteria, which poses a health issue for humans.Using rBGH has also been linked to an increased incidence of birth disorders in calves. Since the introduction of rBGH injections in the dairy industry, the number of calves born with birth defects to dairy cows has increased significantly. Other side effects of rBGH in dairy cows include hoof problems, increased pus in milk, heat stress, and gastrointestinal problems.

Milk products that do not contain rBGH are labeled as such.  In fact, there has been a significant decline in the use of rBGH by dairy farmers since 2002, largely due to increased consumer awareness about its potential health risks.