Testosterone replacement therapy is rising in popularity. What is it and what are there risks?

Testosterone replacement therapy, which involves taking manufactured forms of testosterone, has surged in popularity.  Prescriptions for the treatment rose from 7.3 million in 2019 to more than 11 million last year.

"It's exploding," CBS News chief medical correspondent Dr. Jon LaPook said Tuesday on "CBS Mornings Plus." 

But the treatment, also known as TRT, carries health risks to be aware of. 

And while it is approved by the Food and Drug Administration for some conditions, and is widely marketed as a way to improve health and stay young, data on long-term effects is limited.

"We did a big investigation five years ago, went across the country, and there are a lot of places that are pushing this as a fountain of youth. Who doesn't want to be younger?" LaPook said. "But there are problems."

What is testosterone replacement therapy?

TRT involves the use of anabolic steroids, a synthetic drug, to increase testosterone levels. It can be administered via injection, oral medication or topically with gels or patches. 

Testosterone is a hormone produced primarily in the testicles that helps develop or maintain bone, muscle and fat, as well as facial and body hair, red blood cells, sex drive and sperm production. Though testosterone levels are naturally higher in males, both testicles and ovaries produce testosterone, the Cleveland Clinic notes.

"For adult females, testosterone enhances libido. However, the majority of testosterone produced in the ovaries is converted to the primary female sex hormone, estradiol," the clinic's website reads.

What is testosterone replacement therapy approved for?

The FDA only approves the use of testosterone for people who have symptoms and are hypogonadal, meaning they have a condition that causes lower-than-normal testosterone levels, LaPook said.

"So it's not just a low testosterone. You have symptoms of erectile dysfunction, decreased libido. You're fatigued," he added, advising people to seek proper medical care to determine if this therapy is right for them. "This is something where you don't want to be going online and just getting it and taking it at home and not following the levels. You need somebody who's professional."

How do I know if I have low testosterone?

Multiple blood tests can measure testosterone levels. Before testosterone therapy is recommended, a doctor may test levels multiple times to determine the best treatment option. 

Treating normal aging with testosterone therapy is also not advisable, according to the Mayo Clinic.

"If you don't have a medical condition that's contributing to your decline in testosterone levels, your doctor might suggest natural ways to boost testosterone, such as losing weight and increasing muscle mass through resistance exercise," the clinic notes.

Testosterone replacement therapy risks 

While the treatment may have an impact on muscle strength and how people feel, LaPook said there is limited evidence on the extent of potential benefits and potential dangers.

"Anything that is pharmacologically active and can help, is pharmacologically active and can hurt," LaPook warned. "One of the problems is that there are a lot of people, guys out there who are taking testosterone because they want to feel younger — they want the muscle, they want to get jacked up. But there are problems with it."  

For people with low testosterone using TRT, studies show slight increased risk of certain heart, lung and kidney conditions. But there aren't controlled studies for those using it with normal testosterone levels.

"You're kind of rolling the dice there," he said. 

It could also affect fertility by reducing sperm count, cause acne and worsen sleep apnea, according to both the Cleveland Clinic and Mayo Clinic.

The Cleveland Clinic adds that TRT is also unsafe if you have certain existing health conditions like prostate cancer, breast cancer or heart failure.

"Although some men believe they feel younger and more vigorous if they take testosterone medications, there's little evidence to support the use of testosterone in otherwise healthy men," the Mayo Clinic says.