How testosterone replacement therapy injections can boost your mood

Testosterone replacement therapy injections can lift mood, energy, and sex drive in some men with true low testosterone, but they are not a shortcut or a cure-all. Here is how they work, who they help, and how to use them safely.

The relationship

Testosterone is an androgen, a sex hormone that drives male traits like facial hair, deeper voice, muscle growth, and sperm production. It also talks directly to brain regions that control motivation, reward, and emotional balance.

As men move past their early 30s, testosterone levels often drop about 1% each year. For many, that decline is slow and silent. For others, especially men whose total testosterone falls below about 350 ng/dL (about 12 nmol/L), the brain and body start to notice: mood dips, drive fades, and fatigue creeps in.^[1]

Testosterone replacement therapy injections give back a synthetic form of the same hormone your testes used to make in higher amounts. In men with proven low levels and symptoms, randomized trials show that restoring testosterone into the mid-normal range can modestly improve mood, reduce depressive symptoms, and increase vitality scores on quality-of-life scales.^[2],[3]

How it works

Testosterone replacement therapy injections aim to correct hypogonadism. Hypogonadism means the testes do not make enough testosterone for the body’s needs. The clinical target is usually to move a man from clearly low levels into the mid-normal range without overshooting.

Meta-analyses suggest that symptomatic men with total testosterone below 350 ng/dL or free testosterone below 100 pg/mL are most likely to benefit from testosterone replacement therapy injections when lifestyle steps alone are not enough.^[1]

Injecting testosterone and how it gets into your system

Most testosterone replacement therapy injections use testosterone cypionate or testosterone enanthate. These are esterified forms of testosterone. An ester is a chemical tail that slows release from the muscle into the blood.

The medication is given deep into a muscle, often the glute or thigh. From there, the ester is slowly cut off by enzymes, releasing bioidentical testosterone into circulation over several days.^[4]

Steadying hormone levels to steady mood

When men first start testosterone replacement therapy injections, dosing is often every 1 to 2 weeks. Large doses spaced far apart can cause peaks and crashes in testosterone. These swings can translate into “on” days and “off” days for mood and energy.

Guidelines now favor smaller, more frequent injections to flatten these peaks and valleys. More stable hormone levels appear to be linked with more stable mood and fewer side effects like irritability or acne.^[4],[5]

Talking to brain chemistry

Testosterone interacts with receptors in brain regions such as the amygdala, hippocampus, and prefrontal cortex. These are areas involved in emotion regulation, memory, and decision-making. It also influences neurotransmitters, including serotonin and dopamine, which shape reward, drive, and resilience under stress.^,[2]

Clinical trials in hypogonadal men show that bringing testosterone back into range can reduce scores on depression inventories, ease irritability, and improve self-reported confidence and sexual satisfaction, especially when baseline levels are clearly low.^[2],[3]

Impact on body composition and energy

Testosterone replacement therapy injections do more than change lab numbers. Testosterone promotes protein synthesis, which helps build and maintain muscle, and it reduces fat mass, particularly around the abdomen.^[6]

Over 6 to 12 months, many men on properly dosed injections see increased lean body mass, improved strength, and better exercise capacity. These physical gains can feed back into better mood, improved sleep, and a stronger sense of control over aging.^[6]

Risks, side effects, and the role of estrogen

Some injected testosterone is converted into estradiol, a form of estrogen. Estrogen is a sex hormone that, in men, supports bone health, libido, and aspects of mood. Too little estradiol can cause joint pain and low sex drive; too much can cause breast tenderness or swelling.

Common side effects of testosterone replacement therapy injections include acne, oily skin, higher red blood cell counts, reduced sperm production, and potential fluid retention. Current evidence does not show a major rise in cardiovascular events in well-selected men, but data are mixed and monitoring is essential, especially in older men with heart disease.^[5]

Conditions linked to it

Testosterone replacement therapy injections are not a lifestyle drug. Major guidelines reserve them for men with confirmed hypogonadism and symptoms that affect daily life.^[1]

Clinically relevant situations where injections may be considered include:

• Primary hypogonadism: The testes themselves are failing, often from genetic conditions, infection, trauma, or chemotherapy. Blood tests show low testosterone with high luteinizing hormone, a brain signal trying to push the testes to work.
• Secondary hypogonadism: The hypothalamus or pituitary gland in the brain under-signals the testes. Causes include pituitary tumors, head injuries, certain medications such as opioids, or severe obesity and sleep apnea.
• Age-related low testosterone: Some men in midlife or later develop persistent low levels with clear symptoms, even without a single identifiable disease. Evidence for benefit is strongest when testosterone is consistently below 350 ng/dL and other causes of fatigue or low mood have been addressed.^[1],[3]
• Delayed puberty in adolescent males: Short-term, carefully supervised testosterone replacement therapy injections can “jump start” puberty under specialist care.

Testosterone replacement therapy injections are usually avoided in men with active prostate or breast cancer, untreated severe sleep apnea, uncontrolled heart failure, or those trying to conceive, because injected testosterone suppresses sperm production.^[5]

Limitations note: In men with borderline levels or complex mental health histories, it can be difficult to separate symptoms caused by low testosterone from those driven by depression, anxiety, or burnout. In those cases, guidelines recommend a combined approach: therapy, lifestyle changes, and, where appropriate, a time-limited trial of testosterone replacement therapy injections with close follow-up.

Symptoms and signals

Symptoms of low testosterone are often slow and subtle. Many overlap with common problems like stress, poor sleep, or overwork. Still, there is a recognizable pattern doctors look for along with low lab numbers.

Signals that might prompt a conversation about testosterone replacement therapy injections include:

• Low or fading sex drive that persists for months
• Fewer morning erections than in the past
• Difficulty achieving or maintaining erections despite interest
• Unusual fatigue even after decent sleep
• Noticeable drop in motivation, drive, or competitiveness at work or in hobbies
• Low mood, irritability, or a “flat” emotional state without clear cause
• Loss of muscle mass or strength despite regular activity
• Increase in belly fat or overall body fat
• Reduced shaving frequency due to slower beard growth
• Decreased stamina during exercise or everyday tasks like climbing stairs
• Difficulty concentrating, “brain fog,” or slower mental sharpness
• Lower bone density or fractures from minor falls

None of these symptoms prove that testosterone is the problem by themselves. Yet when several cluster together, especially alongside low blood levels on repeat morning tests, testosterone replacement therapy injections may enter the conversation.

What to do about it

If you think low testosterone might be affecting your mood or energy, there is a practical way to move from guesswork to a clear plan.

1. Step 1: Get properly tested
   Ask your clinician for at least two early-morning blood tests for total testosterone, done between 7 a.m. and 10 a.m. If total testosterone is borderline, free testosterone and sex hormone–binding globulin help clarify the picture.^[1] Your doctor should also screen for thyroid disease, anemia, vitamin deficiencies, depression, and sleep apnea, which can mimic low testosterone.
2. Step 2: Fix fundamentals and weigh treatment options
   Before jumping to testosterone replacement therapy injections, improve sleep, reduce alcohol, manage weight, and increase resistance training. These can raise testosterone modestly and improve mood even without medication.^[6] If you still have symptoms and labs show testosterone below about 350 ng/dL or free testosterone below 100 pg/mL, discuss treatment options with your clinician. Injections are often the most cost-effective and reliable form, but gels, patches, or pellets may suit some men better. You can also learn more about broader testosterone replacement therapy side effects and management as you weigh options.
3. Step 3: Start low, monitor, and adjust
   If you and your doctor choose testosterone replacement therapy injections, doses typically start around every 1 to 2 weeks, then are adjusted based on symptoms and mid-interval blood levels. Ongoing monitoring should include testosterone, estradiol, blood counts, prostate-specific antigen, and blood pressure at least every 6 to 12 months.^[5] It is also worth understanding common testosterone replacement therapy side effects and how they are usually monitored and managed over time.

Myth vs Fact

• Myth: “Testosterone replacement therapy injections are just legal steroids for muscle building.”
  Fact: Medical TRT aims to restore normal levels in men who are low, not to push levels into bodybuilding ranges. Proper dosing focuses on health, mood, and function, not extreme muscle gain.
• Myth: “Once you start injections, you can never stop.”
  Fact: Some men with reversible causes of low testosterone can taper off under medical guidance. For men with permanent testicular or pituitary damage, long-term treatment may be needed, but it is a shared decision, not a trap.
• Myth: “TRT will fix depression by itself.”
  Fact: Testosterone can improve mood in men with true hypogonadism, but it does not replace therapy, lifestyle changes, or, when needed, antidepressant medication. Mental health needs a multi-tool approach.
• Myth: “TRT causes prostate cancer.”
• Fact: Current evidence does not show that physiological replacement doses increase prostate cancer risk, but they can stimulate growth of existing cancer, which is why screening and monitoring are crucial.
• Myth: “If a little testosterone helps, more is always better.”
  Fact: Overshooting into high ranges increases risks such as thickened blood, sleep apnea, mood swings, and infertility without proven added mood benefit.

Beyond hormones, men considering testosterone replacement therapy injections can take several practical steps to support mood and resilience:

• Protect sleep: Aim for 7 to 9 hours of consistent, high-quality sleep. Poor sleep can cut testosterone levels and worsen mood even if hormones are corrected.
• Lift something heavy: Two to three sessions of resistance training per week support testosterone, muscle, and mental health.
• Limit alcohol and nicotine: Both can lower testosterone and worsen sleep and anxiety. If you use nicotine, it may help to understand how nicotine impacts testosterone and overall hormone health.
• Address stress directly: Structured stress-management, such as cognitive behavioral therapy, mindfulness, or coaching, can help you use any boost from TRT more effectively.
• Include your partner: Discuss expectations, benefits, and risks together. Mood and libido changes affect relationships, not just the individual.

Bottom line

For men with clearly low testosterone and persistent symptoms, testosterone replacement therapy injections can be a powerful tool to restore mood, energy, sex drive, and physical capacity. The benefits are real but usually moderate, and they depend on careful testing, individualized dosing, and ongoing monitoring. When injections are paired with solid sleep, movement, and mental health strategies, many men describe not just feeling “younger,” but more like themselves again.

References

1. Bhasin S, Brito JP, Cunningham GR, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. The Journal of clinical endocrinology and metabolism. 2018;103:1715-1744. PMID: 29562364
2. Walther A, Breidenstein J, Miller R. Association of Testosterone Treatment With Alleviation of Depressive Symptoms in Men: A Systematic Review and Meta-analysis. JAMA psychiatry. 2019;76:31-40. PMID: 30427999
3. Snyder PJ, Bhasin S, Cunningham GR, et al. Effects of Testosterone Treatment in Older Men. The New England journal of medicine. 2016;374:611-24. PMID: 26886521
4. Wang C, Nieschlag E, Swerdloff R, et al. ISA, ISSAM, EAU, EAA and ASA recommendations: investigation, treatment and monitoring of late-onset hypogonadism in males. International journal of impotence research. 2009;21:1-8. PMID: 18923415
5. Mulhall JP, Trost LW, Brannigan RE, et al. Evaluation and Management of Testosterone Deficiency: AUA Guideline. The Journal of urology. 2018;200:423-432. PMID: 29601923
6. Corona G, Giagulli VA, Maseroli E, et al. Testosterone supplementation and body composition: results from a meta-analysis of observational studies. Journal of endocrinological investigation. 2016;39:967-81. PMID: 27241317