FDA’s Safety Assessment of rbGH
Consumers Union questions the US Food and Drug Administration (FDA) review and approval of recombinant bovine growth hormone (rbGH) after Health Canada investigated a 1989 90-day Monsanto rbGH rat feeding study and found toxicologically significant changes in the rats. This means that when rbGH was fed to laboratory rats, a proportion of those rats showed some type of biological changes that could be of concern. In an earlier article in Science magazine, the FDA earlier claimed the rats showed no toxicologically significant changes. Health Canada, Canada's equivalent of the FDA, has since banned rbGH.
You can read the FDA's response to the criticism here, where the Agency responds that "the Canadian reviewers did not interpret the study results correctly and that there are no new scientific concerns regarding the safety of milk from cows treated with rbGH."