Men take testosterone shots primarily to treat low testosterone, a condition called hypogonadism that affects an estimated 2 to 6 million men in the United States. The American Urological Association defines low testosterone as a total level below 300 ng/dL, measured through a blood test. When levels drop below that threshold, a range of symptoms can follow: low sex drive, fatigue, depressed mood, loss of muscle mass, and difficulty concentrating. Testosterone injections restore levels to a normal range and, in most cases, reverse those symptoms.
Low Testosterone and Its Symptoms
Testosterone production naturally declines with age, dropping roughly 1 to 2 percent per year after age 30. But age isn’t the only cause. Injury to the testicles, pituitary gland disorders, obesity, chronic opioid use, and certain genetic conditions can all suppress production. Some men develop symptoms in their 30s or 40s; others don’t notice anything until their 50s or 60s.
The symptoms tend to creep in gradually, which is part of why many men don’t recognize them right away. Low energy, irritability, brain fog, reduced motivation, and a noticeably lower interest in sex are among the most common complaints. Over time, men may also lose lean muscle, gain belly fat, and notice weaker erections. Because these overlap with stress, poor sleep, and aging in general, the only way to confirm low testosterone is a blood test, typically drawn in the morning when levels peak.
Sexual Health Improvements
Restoring sex drive is one of the most common reasons men start testosterone therapy. In a major trial of older men with confirmed low testosterone, those treated with testosterone showed consistent improvement in libido and in 10 of 12 sexual activity measures, including frequency of intercourse, masturbation, and nighttime erections. For many men, the decline in sexual interest was the symptom that prompted them to get tested in the first place, and it tends to be one of the first things to improve once treatment begins.
Erectile function can also improve, though testosterone alone doesn’t always resolve erectile dysfunction. Blood flow, nerve function, and psychological factors all play a role. Men with both low testosterone and erectile problems sometimes need additional treatment, but correcting the hormonal piece often makes a noticeable difference.
Mood, Energy, and Mental Clarity
Low testosterone doesn’t just affect the body. It has a measurable effect on mental health. Men who’ve been on testosterone therapy for 12 months or longer show lower scores on standardized measures of depression, anxiety, and attention problems compared to similar men not receiving treatment. The effect on attention and focus tends to be the most pronounced, while mood improvements, though real, are more modest.
Many men describe the mental shift as getting out of a fog. Tasks that felt overwhelming become manageable again. Motivation returns. The flat, dulled feeling that settled over daily life starts to lift. These changes don’t happen overnight. Most men notice gradual improvement over the first several weeks, with mood and energy stabilizing over three to six months.
Body Composition and Metabolic Health
Testosterone plays a direct role in how the body builds muscle and stores fat. Men on therapy typically gain lean muscle mass and lose visceral fat (the deep belly fat linked to heart disease and diabetes) even without major changes to their exercise routine, though the results are better when combined with resistance training.
The metabolic effects go deeper than appearance. In a long-term study of men with both low testosterone and type 2 diabetes, those treated with testosterone experienced significant, sustained reductions in body weight, fasting blood sugar, and long-term blood sugar markers. One-third of the treated men saw complete remission of their diabetes, and 83 percent reached their target blood sugar levels. The control group, by contrast, saw no remission and their blood sugar markers actually worsened over time. Low testosterone contributes to insulin resistance, and correcting the deficiency appears to partially reverse that metabolic dysfunction.
How the Injections Work
The most common form of testosterone replacement is an intramuscular injection, typically using testosterone cypionate or testosterone enanthate. The FDA-approved dosing range for cypionate is 50 to 400 mg administered every two to four weeks as a deep injection into the gluteal muscle. In practice, many prescribers split this into smaller, more frequent doses (often weekly) to keep blood levels more stable and reduce the peaks and valleys that can cause mood swings or energy dips between injections.
Some men learn to self-inject at home after an initial demonstration, while others visit a clinic. The injection itself takes less than a minute. Blood work is checked periodically to ensure testosterone levels are in the target range and to monitor for side effects.
Side Effects and Monitoring
Testosterone therapy is generally well tolerated, but it does require ongoing monitoring. The most common issue is a rise in hematocrit, the percentage of red blood cells in your blood. Testosterone stimulates red blood cell production, and if hematocrit climbs too high, it thickens the blood and raises the risk of clots. Guidelines from the Endocrine Society flag a hematocrit of 54 percent as the threshold for dose adjustment or temporary cessation, while the AUA recommends closer attention starting at 50 percent. Regular blood draws catch this early.
Other potential side effects include acne, oily skin, fluid retention, and breast tenderness. Sleep apnea may worsen in men who already have it. Most side effects are manageable with dose adjustments.
On the cardiovascular front, the largest safety trial to date (the TRAVERSE study, involving over 5,000 men) found no increased risk of heart attack, stroke, or cardiovascular death in men using testosterone compared to placebo. The rates of major cardiac events were nearly identical between the two groups, at 7.0 percent and 7.3 percent respectively.
The Fertility Trade-Off
This is one of the most important things men considering testosterone shots need to understand: testosterone injections suppress sperm production, often dramatically. The brain interprets the incoming testosterone as a signal that the body is making enough, so it stops sending the hormones that tell the testicles to produce sperm. In studies, 100 mg of testosterone enanthate per week triggered complete absence of sperm in all participants by week 20. At higher doses, it can happen even faster, within about 12 weeks.
For men who want children now or in the near future, this is a serious consideration. Alternative treatments exist that can raise testosterone while preserving fertility, and these are typically the first-line approach for younger men.
The good news is that sperm production does recover after stopping injections. Most men see a return to pre-treatment sperm counts within 6 to 12 months, and after 12 months, more than 98 percent of men in studies recovered normal sperm production. Recovery can sometimes be accelerated with targeted medications. Still, the timeline varies, and there’s a small risk that full recovery doesn’t happen, particularly after very long-term use.
Who Gets Prescribed Testosterone Shots
Testosterone therapy isn’t appropriate for every man who feels tired or notices a dip in libido. A proper diagnosis requires at least two morning blood tests showing total testosterone below 300 ng/dL, along with symptoms consistent with deficiency. Some medical societies use slightly different cutoffs, ranging from 230 to 350 ng/dL, but the 300 ng/dL threshold is the most widely referenced in the U.S.
Men with a history of prostate cancer, untreated severe sleep apnea, uncontrolled heart failure, or very high red blood cell counts are generally not candidates. For everyone else, the decision comes down to whether the symptoms are significant enough to warrant lifelong treatment, because testosterone therapy is, for most men, an ongoing commitment. Stopping treatment means testosterone levels will drop back to where they were, and symptoms will return.