WASHINGTON — Drugmaker Endo Pharmaceuticals said Thursday that it received U.S. approval for its long-acting testosterone injection, Aveed, which joins a crowded field of hormone-boosting drugs aimed at aging American men.

The Irish drugmaker said the Food and Drug Administration (FDA) approved Aveed for men with low testosterone, a condition sometimes associated with fatigue, weight gain and low libido.

Endo’s injection is to be taken once every 10 weeks, versus weekly or biweekly dosing for currently available products. The company said it expects to launch the drug this month. The Dublin-based company also markets Fortesta, a prescription gel form of testosterone, the male hormone that begins to decline after age 40.

The FDA approval comes amid growing scrutiny of popular testosterone drugs.

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In January, the FDA said it was reviewing the safety of the drugs after a federal study of 45,000 patients suggested testosterone therapy could double the risk of heart attack in men 65 and older. Last month, the consumer-advocacy group Public Citizen called on FDA regulators to add a bold warning label about the cardiovascular risks to all testosterone drugs.

The Aveed approval was criticized by Public Citizen’s Health Research Group founder Dr. Sidney Wolfe, who sent a letter to the FDA on Thursday asking it to reverse its decision. He noted that an FDA panel of outside advisers issued a split opinion on Aveed’s safety last year, voting 9-9 on the question of whether the drug was safe for treatment of low testosterone. He added that the meeting, held last April, did not include a discussion about heart risks.

“It is likely, if not certain, that the vote against safety would have been even greater had there been a presentation and discussion of the cardiovascular risks known at that time,” Wolfe states.

FDA spokeswoman Andrea Fischer said the FDA is continuing its review of testosterone products, but there is no evidence that Aveed’s risks are any greater than those of other testosterone drugs already on the market.

U.S. prescriptions for testosterone therapies have increased more than fivefold in recent years, with sales exceeding $1.6 billion.

FDA labeling on the drugs states that they are only to be used by men who have been diagnosed with hypogonadism, a form of abnormally low testosterone caused by injury or illness.

But the latest advertising push by drugmakers has focused on otherwise healthy older men with lower-than-normal levels of testosterone.