A man doing back squat

Yes, Testosterone Injections Actually Build Muscle. Here’s How.

The catch: TRT should only be used if you’re testosterone deficient. We’ll explain why.

Low testosterone can be a gut punch to your gains. Despite your all-out effort in the gym, you’re left sore—and often more weak—post-pump.

That’s because testosterone plays a vital role in muscle strength and size. If your levels nosedive to a below-normal range, you’ll notice nasty symptoms including weight gain, fatigue, and—yes—muscle loss.

While testosterone injections are not the same as using anabolic -androgenic steroids (more on that below), testosterone replacement therapy (TRT) can get your hormone levels back on track and help you boost muscle gains. But it isn’t an overnight fix. You may see changes to lean body mass and muscle strength in the first three months of treatment, but it can take a year or longer to see the full impact (1).

We asked physical medicine and rehabilitation physician Matthew Cowling, D.O.—who is also an active bodybuilder and CrossFitter—about the best ways to build muscle in tandem with TRT. Here’s what he said.

How Does Low T Impact Muscle Growth?

Testosterone stimulates muscle growth by binding to proteins in your muscles called androgen receptors, explains Cowling.

If your natural testosterone levels are below what they should be for your age, there simply isn’t enough of the hormone to activate the androgen receptors and spur gains, even if you spend hours strength training, says Cowling.

Checking your T levels is easy with Hone’s at-home assessment. You can knock it out before your AM coffee. 

How Does Testosterone Make You Stronger?

TRT increases your testosterone levels (obviously).

“As testosterone levels increase, your androgen receptors are activated, increasing the rate of muscle growth,” Cowling says.

Higher T levels also increase a muscle-stimulating hormone called IGF-1, which activates growth hormone—which helps build your bones and muscles—causing nitrogen retention (2). Because proteins are largely made of nitrogen-containing amino acids, Cowling says, it’s likely that you need to retain more nitrogen to see muscle growth.

Where does muscle growth occur the most?

Individual genetics play a role in where exactly you’ll build muscle, but many men on TRT notice the biggest difference to size and strength in their traps and shoulders, says Cowling, because your traps have the most androgen receptors.

A man at the gym doing twists with a medicine ball

How to Build Muscle on TRT

TRT only plays a small role in muscle growth, Cowling says. “You can’t build muscle without proper exercise, nutrition, sleep, and recovery,” he says.

weight training program can help you build and maintain muscle as your T levels get back to normal, Cowling says. “It doesn’t matter which training plan you use as long as you incorporate the principles of progressive overload so your muscles grow and adapt,” he says. Progressive overload, where you increase time, weight, or intensity by 10 percent each week will help you avoid injury and training plateaus so your growth doesn’t stall.

Work some runs or HIIT sessions into your workout regimen. Cardio builds lean muscle and may counteract age-related muscle loss (3). “A good program should involve a mix of the two,” says Cowling. Fuel your muscle growth with a high-protein diet, since protein is the building block for muscle. Eating at least one gram of protein per pound of bodyweight per day will maximize muscle building (a 200-pound guy equals about 200 grams of protein).

TRT is Not the Same as Illegal Steroids

So much so, we’ll say it again: TRT is not the same as taking illegal steroids.

The main difference between taking testosterone illegally and using TRT is the dosage, Cowling says.

“Professional or recreational bodybuilders use much higher doses of T than you would see for TRT,” says Cowling. “This often starts at 500 mg per week as a minimum whereas a normal dose of testosterone for TRT could vary from 125 mg to 200 mg per week.”

While steroid use operates in an unregulated, unsafe, and illegal market, testosterone therapy is closely monitored by your doctor to find the right dose.

From Steroids to TRT

What Are the Side Effects of Testosterone Therapy?

TRT doesn’t come side effect-free. It’s hard to predict what side effects—if any—will strike, but the most common include:

If you do experience the following symptoms, your doctor will either lower your dose or take you off treatment.

Considering TRT?

Checking your testosterone levels is easier than ever with an At-Home Testing Kit. Men who start TRT report benefits including higher sex drive, more energy, weight loss, increased cognitive functioning, and muscle mass.

If your T levels are clinically low, a doctor will work with you to address your symptoms to optimize your health.

The Bottom Line

Testosterone injections activate androgen receptors in your muscle fibers and stimulate muscle building hormones—including IGF-1—to build muscle, but you shouldn’t use TRT unless you’re testosterone deficient. If you suspect low testosterone levels are the reason you’re struggling to build muscle, order a test to check your levels.