Both the European Food Safety Authority (EFSA) and the United States Food and Drug Administration (FDA) have evaluated TBHQ and determined that it is safe to consume at the concentration allowed in foods. The FDA sets an upper limit of 0.02% of the oil or fat content in foods.
At very high doses, it has some negative health effects on lab animals, such as producing precursors to stomach tumors and damage to DNA.
A number of studies have shown that prolonged exposure to very high doses of TBHQ may be carcinogenic, especially for stomach tumors. Other studies, however, have shown opposite effects including inhibition against HCA-induced carcinogenesis (by depression of metabolic activation) for TBHQ and other phenolic antioxidants (TBHQ was one of several, and not the most potent). The EFSA considers TBHQ to be noncarcinogenic. A 1986 review of scientific literature concerning the toxicity of TBHQ determined that a wide margin of safety exists between the levels of intake by humans and the doses that produce adverse effects in animal studies. Michigan State University scientists are studying a possible link between TBHQ and food allergies.