TESTOSTERONE IS AN ESSENTIAL hormone for your body. It helps you maintain muscle mass, facial and body hair, sex drive, and red blood cell production. So when your levels are low, also known as low T, you can experience many symptoms.
When you have low T, you might need testosterone therapy to boost your levels and reduce your symptoms.
“Testosterone therapy supplements or replaces an important hormone produced naturally by your body in those men with testosterone deficiency,” says Darshan Patel, M.D., assistant professor of urology at the University of California San Diego’s Men’s Health Center.
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As you age, your levels of testosterone tend to decline. And that can be problem: Testosterone binds to proteins throughout your body and brain called androgen receptors, which help control and regulate a whole range of different bodily functions, explains Ronald Tamler, M.D., Ph.D., associate professor of medicine at the Icahn School of Medicine at Mount Sinai.
If there’s not enough testosterone to go around, those androgen receptors all over your body and brain stay silent, leading to symptoms like low libido, weak erections and orgasms, inability to build muscle mass, low energy, or just feeling blue. A condition called hypogonadism develops when your body can’t produce enough of that hormone.
Testosterone replacement therapy helps raise your low testosterone levels. If you are prescribed testosterone therapy, you’ll likely start to see some changes, big and small, pleasant and not-so-pleasant. You may not see them all, but if you do see them, they may not all appear right away, but there are several things to know about testosterone therapy.
What is testosterone therapy?
Testosterone therapy is designed to reverse some of the effects of hypogonadism.
Doctors will test your testosterone levels to see if you’re a good candidate for the therapy, says Ryan Smith, M.D., associate urology professor and urologic microsurgeon specializing in men’s health at the University of Virginia Health.
They’ll perform two blood tests in the morning (on different days) when testosterone is at its highest, Dr. Smith explains. Low is considered under 300 nanograms per deciliter (ng/dL) by some accounts, 264 by others. Doctors also factor in any symptoms you’re having, like low libido, fatigue, or just feeling blah.
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There are numerous types of testosterone therapy out there: injectibles, topical gels, cream patches, under-the-skin pellet therapy, pills, and nasal sprays, says Dr. Patel. Each comes with its own set of unique side effects.
Which treatment is right for you comes down to personal preference, your individual situation, and what your insurance covers, says Dr. Tamler.
Why you should take testosterone under a doctor’s supervision
Testosterone is often easy to get online without a prescription. But taking it without a doctor’s approval and supervision can be harmful, says Justin Dubin, M.D., a urologist and men’s health specialist at Memorial Healthcare System.
In a 2022 study that Dr. Dubin co-authored, researchers found that many online platforms are not providing testosterone therapy in accordance with the American Urological Association and Endocrine Society guidelines. Using a secret shopper, they found that the platforms offered therapy to men who didn’t meet the guidelines and didn’t mention the risks or benefits of testosterone therapy.
Working with a doctor ensures that you’re prescribed testosterone only when you need it and that you’re taking the right dose. Then, they can work with you to make sure your testosterone levels respond appropriately. They like to recheck everything every six months to make sure you’re not having any negative side effects.
Testosterone therapy side effects
It can take a few weeks to a month or two to see your symptoms improve after starting testosterone replacement therapy, Dr. Smith says. Here are some of the side effects—good and bad—that come with testosterone therapy:
1. Effect of testosterone: Your sex drive jumps
When you’re low on testosterone, you might notice your sex drive dip. Testosterone replacement can activate the androgen receptors in the part of your brain that controls desire, says Abraham Morgentaler, M.D., clinical associate professor of urology at Harvard Medical School; and author of Testosterone for Life.
Regaining a healthy sex drive is one of the biggest benefits of testosterone replacement therapy, he says. T-therapy can possibly make your erections more satisfying, too.
This isn’t the only piece of the puzzle, though—erections also rely on healthy nerves and blood flow. That means that testosterone therapy by itself won’t always help erectile dysfunction.
2. Effect of testosterone: It’s a little easier to build muscle
Muscles respond to testosterone, and starting T-therapy can increase muscle mass, says Dr. Morgentaler. That’s because testosterone activates the androgen receptors in muscle tissue to stimulate growth.
The effect of a testosterone replacement dose on your muscles, however, is fairly minimal. To make the most of this benefit, you’ll need to be doing your part by strength training as well, and possibly raising the amount of protein you consume (depending on what you consume now). He cautions that while testosterone replacement therapy may strengthen muscle, it won’t turn you into a bodybuilder on its own.
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Some men also report fat loss. While testosterone doesn’t directly incite fat loss itself, part of it may be thanks to the uptick in muscle mass—the more muscle you have, the higher your basal metabolic rate (or BMR) will be, which means your body will burn more calories at rest.
Jed Kaminetsky, M.D., a clinical assistant professor in the department of urology at NYU Langone Medical Center also notes that this may be partially because testosterone improves overall motivation to get up and sweat it out, so if you’re motivated to put in the work again, you’ll see results.
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3. Effect of testosterone: Your energy levels can soar
Fatigue is a common symptom of low T. “And when we treat them, a lot of men will say that their energy has improved,” says Dr. Morgentaler.
While researchers aren’t exactly sure how exactly testosterone plays a role in energy yet, he says it’s believed it might affect your mitochondria, which produce energy within cells. The theory is that “testosterone turns them on, so they’re more productive in terms of creating the energy that the cells need.”
Dr. Tamler also notes that it may be tied back to androgen receptors. “If they don’t get sufficient input, that can cause fatigue,” he says. So bringing testosterone levels back up can help reverse this.
4. Effect of testosterone: Your mood can improve
Experts don’t have a definitive answer to why testosterone impacts mood so deeply—after all, “the brain is a complicated thing,” says Dr. Tamler. But the positive benefits of T therapy on mood is a potential life-changing benefit.
A study published in The Aging Male found that after 12 months of testosterone therapy, the percentage of guys with moderately severe to severe depression symptoms decreased from 17 percent to 2 percent. And a large randomized trial of testosterone, the T Trials, showed that men who received T had a greater improvement in mood than men who received a placebo.
5. Effect of testosterone: It’s likely to affect your fertility
One of the most important things to know about testosterone therapy is that it can decrease sperm production and pose a risk of infertility.
It might affect the size of your testicles, too. “Most of the size of the testicle is dedicated to making sperm, so when you’re making less sperm, the testicles get smaller,” says Dr. Morgentaler.
Sperm production may or may not go back to normal after stopping treatment, says Dr. Kaminetsky. A 2017 study in Fertility & Sterility found that increasing age and longer length of T-therapy were linked to lower chances of normal sperm recovery.
6. Effect of testosterone: Your feet and ankles may swell
Some people notice a little swelling in their feet and ankles because testosterone can encourages your body to hold onto excess fluid, says Dr. Morgentaler.
This isn’t a big deal for most people, he says, and its more common to see it if you’re taking a non-daily treatment like an injection, where you’re getting a higher dose of T in one sitting.
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7. Effect of testosterone: Your skin type may change
Testosterone replacement therapy may change your skin type—for better or for worse, says Dr. Morgentaler.
Testosterone can increase oil production, which isn’t necessarily a bad thing. It’s important for healthy skin, so you may actually end up with a better complexion. However, too much oily buildup can lead to breakouts.
Thankfully, this isn’t that common, says Dr. Morgentaler, and it’s typically seen in men who have a history of acne.
Skin changes are mainly seen with treatments like injections, when you’re getting a higher dose all at once.
8. Effect of testosterone: Your breasts may enlarge
In all men—whether you’re taking T or not—some testosterone is converted into the hormone estradiol, a form of estrogen. And in men who have more breast tissue by nature, the T they’re taking that’s naturally converted into estradiol could stimulate this breast tissue to grow.
This is called gynecomastia, says Dr. Morgentaler, and it’s not as common as other side effects. If it does happen, your doctor will likely stop treatment for a month or two to allow your breast tissue to go back to normal, and then start you back up with T along with a drug that blocks the conversion of testosterone to estradiol.
9. Effect of testosterone: You can transfer the hormone to others
One thing to worry about if you’re going the topical testosterone therapy route is transference, especially to female partners or children, Dr. Patel says. Testosterone from gels or creams can be spread from skin-to-skin contact or from your clothing and absorbed by someone else.
“You really have to be careful to wash your hands well and not expose others,” Dr. Smith says. Contact with excess testosterone can affect children’s genitalia and cause premature pubic hair development and aggressive behavior.
10. Effect of testosterone: The link between testosterone and serious risks is still murky
Testosterone replacement therapy has traditionally come along with serious warning labels that your risk for heart attack, stroke, and prostate cancer could rise, but this is still very controversial—and recent evidence has begun to debunk some of these fears.
In the case of heart attacks and strokes, the concern is that testosterone thickens blood because it binds to androgen receptors that stimulate bone marrow to produce more red blood cells. Thicker blood is linked to a greater risk of heart attack and stroke. But some recent studies actually suggest that normal testosterone levels might actually protect against these risks, says Dr. Morgentaler.
TRT—especially injectable testosterone and transdermal treatments to a lesser extent—also elevates your red blood cell count. Doctors don’t know exactly what this means to your health in the long or short term. But watching over these levels is another reason you should be under a doctor’s care when taking testosterone.
In a large study published in the New England Journal of Medicine in 2023, men who got testosterone replacement to correct for hypogonadism didn’t have a greater number of cardiovascular events than similar guys who took a placebo. However, there was a higher incidence of pulmonary embolism, acute kidney injury, and atrial fibrillation among men who received testosterone replacement.
As for the risk of prostate cancer, the link to prostate cancer is fuzzy. Because there are androgen receptors in the prostate, testosterone can make it grow. So if you already have an enlarged prostate that makes it difficult to urinate, testosterone could exacerbate the issue, says Dr. Tamler. However, there isn’t evidence to suggest that T actually causes prostate cancer.
Is Testosterone Therapy Safe?
Testosterone replacement therapy is safe and approved by the U.S. Food and Drug Administration for men with a testosterone deficiency, Dr. Patel.
And, it’s safe as long as you follow your doctor’s orders and don’t seek it out on your own. “It requires regular monitoring by your doctor,” he adds.
While there are several myths about testosterone therapy and the risk of cardiovascular disease and prostate cancer, there’s no conclusive evidence, Dr. Patel emphasizes. “This is an ongoing area of research.”
