How do I know if I need testosterone? If you are a man who feels your energy and sex drive have decreased, have your doctor do a blood test to see if your testosterone is low.

"Testosterone should only be used with a clinical indication, meaning clinical signs and low lab values," Dr. Ryan Terlecki, assistant professor of urology at Wake Forest Baptist Medical Center, told ABC News.

Dr. Michael O'Leary, a senior urologic surgeon at Brigham and Women's Hospital, said many of his patients request testosterone.

"The questions patients ask are the ones they see on television," he said. "Direct to consumer marketing may be creating this disease entity. I'm not saying it doesn't exist, but an awful lot of men come in and their testosterone is just fine. Testosterone replacement is not the answer. It's not a panacea."

What side effects does testosterone have? Testosterone can cause infertility and increase the number of red blood cells in the body, resulting in hyperviscosity, Terlecki told ABC News. It should also not be taken if you have prostate cancer.

"Testosterone used appropriately does not cause prostate cancer," said Terlecki. "However, it might have negative effects with untreated prostate cancers. Also in patients with a history of prostate cancer, testosterone should be used with caution."

What results can you expect if you take testosterone? The effects of testosterone vary from person to person. While some people experience increased sex drive and more energy, the results are not universal.

O'Leary tells his patients that they should be in tune with their bodies and make note of any changes they experience, instead of having specific expectations.