Low testosterone treatments were slapped with another black-box warning—adding a general risk of blood clots in the veins to a growing list—FDA announced this past Friday.

The agency already had required testosterone-product labeling to mention risk of blood clots, due to polycythemia—or an abnormal increase in the number of red blood cells that often accompanies testosterone treatment.

FDA revised its initial guidance to include a general warning for risk of blood clots in the veins due to evidence from postmarket reports showing that venous blood clots were forming unrelated to polycythemia.

The category includes blockbuster AbbVie testosterone treatment Androgel, which reported $1.4 billion in US sales for 2013. Auxilium, which manufactures the testosterone replacement therapy gel Testim, announced that drugmaker Prasco would launch an authorized generic of its drug starting on June 11, 2014.

In February this year, FDA stated that low-T treatments may be associated with an increased risk of death, heart attack and stroke. A month later, The EMA (European Medicines Agency) said it, too, would conduct a risk assessment of testosterone treatments.

The announcement was sparked by a JAMA study which suggested the treatments are associated with cardiovascular safety issues, concluding, “Among a cohort of men in the VA health care system who…had a low serum testosterone level, the use of testosterone therapy was associated with increased risk of adverse outcomes.”

Another study by PLoS ONE also observed “a two-fold increase in the risk of MI [heart attack]” after filling an initial prescription, and that that risk then “declined to baseline…after initial TT prescription, among those who did not refill their prescription.”

The FDA did note that the new warning was unaffected by the agency’s ongoing assessment of adverse outcomes.