In recent years, Spyros Mezitis, MD, PhD, has found himself talking to a lot more male patients about low testosterone, a diagnosis he says is becoming increasingly common.

"More men are getting older, and men are more open about talking about erectile dysfunction," Mezitis, an endocrinologist at Lenox Hill Hospital in New York City, tells WebMD.

On the one hand, increased diagnosis of low testosterone is driven by an aging population, less stigma, and more precise tests. But there's another big reason why men come to Mezitis' office for a testosterone test.

"Men are bombarded by media, by advertising campaigns -- 'Don't feel well? Ask your doctor about low testosterone,'" he says.

They come in saying they feel excessively fatigued, weaker, depressed, and that they have lost their sex drive -- all common symptoms of a drop in testosterone.

"As an endocrinologist, I'm thinking hormones," says Mezitis, who estimates that about a quarter to a third of the men he tests for low testosterone have levels below normal. "Sometimes it is testosterone, sometimes it is the thyroid, and sometimes it's something unrelated to hormones."