Last updated: October 2026.
Quick answer: Testosterone replacement therapy (TRT) is prescription testosterone for men who have symptoms and consistently low morning levels on two blood tests. It may improve sex drive, mood and body composition. It also lowers sperm production, can thicken the blood and needs regular monitoring. It is not advised for men trying to conceive or for normal ageing alone.
Testosterone replacement therapy is widely advertised, and online clinics have made it easy to get. It helps when a real deficiency is confirmed, and it carries risks and a long-term commitment.
This guide explains who qualifies, how the forms compare and what monitoring involves. If you have not been tested yet, start with how to check testosterone levels.
Testosterone replacement therapy at a glance
| Question | Short answer |
|---|---|
| What it is | Prescription testosterone that brings low levels back into the normal range |
| Who qualifies | Men with symptoms plus low morning testosterone on two separate tests |
| Usual threshold | Total testosterone below about 300 ng/dL |
| Forms | Injections, gels, patches, pellets, oral capsules, nasal gel |
| Most likely benefit | Better sex drive; smaller gains in mood, muscle and bone density |
| Main risks | Thicker blood, infertility, acne, possible worsening of sleep apnea |
| Monitoring | Testosterone, hematocrit and PSA blood tests |
| Duration | Usually long term; levels fall again if you stop |
What is testosterone replacement therapy?
Testosterone replacement therapy is medical treatment that supplies testosterone from outside the body to men whose own production is too low. The condition it treats is called hypogonadism or testosterone deficiency.
The goal is a level in the middle of the normal range, not a high level.
TRT replaces the hormone and does not fix the cause. When testosterone comes from outside, the brain signals the testicles to make less, which is why sperm production falls during treatment.
Who qualifies for TRT?
Men qualify for testosterone replacement therapy when they have symptoms of deficiency and consistently low total testosterone on two early-morning blood tests. Endocrine Society and American Urological Association guidelines both require symptoms and numbers together.
- Symptoms: low sex drive, fewer morning erections, erectile problems, fatigue or low mood. See the full list of low testosterone symptoms.
- Blood tests: two morning samples, ideally fasting, on different days. Below about 300 ng/dL is the usual threshold.
- Work-up: LH and FSH tests to find the cause, plus a baseline hematocrit and PSA.
A single low result or symptoms with normal levels are not enough. Doctors also look for treatable causes first, such as obesity, sleep apnea and opioid use.
Who should not take TRT?
Men who want to father a child in the near future should not take testosterone replacement therapy, because it suppresses sperm production. Guidelines also list several conditions in which treatment is usually avoided or delayed.
Typical guideline cautions are:
- plans to conceive in the near term
- prostate cancer or male breast cancer that is untreated or active
- a raised PSA or a prostate nodule that has not been evaluated by a urologist
- a high hematocrit (thick blood) before treatment
- untreated severe obstructive sleep apnea
- a heart attack or stroke in the past several months
- uncontrolled heart failure or a tendency to form blood clots
This is not a complete list. Men with past prostate cancer need a specialist’s opinion.
Which form of TRT is best?
No form of testosterone replacement therapy is best for everyone. The choice depends on cost, convenience and who lives with you, and all approved forms can bring levels into the normal range.
| Form | How often | Pros | Cons |
|---|---|---|---|
| Injections (cypionate, enanthate) | Usually every 1 to 2 weeks | Low cost; can be self-injected | Peaks and dips in levels; higher rate of thick blood |
| Long-acting injection (undecanoate) | About every 10 weeks after loading doses | Few doses a year | Given in a clinic, with observation afterward |
| Gels | Daily, on the skin | Steady levels; no needles | Can transfer to women and children by skin contact |
| Patches | Daily | Steady levels | Skin irritation is common |
| Pellets | Every 3 to 6 months | Nothing to remember day to day | Minor office procedure; dose is hard to adjust |
| Oral undecanoate capsules | Twice daily with food | No needles, no skin transfer | Can raise blood pressure; often costly |
| Nasal gel | Two or three times a day | Short acting; no skin transfer | Frequent dosing; nasal irritation |
Older oral methyltestosterone is not recommended because of liver risks.
What benefits can you expect, and how soon?
The most consistent benefit of TRT is a better sex drive, which often improves within the first weeks to months. Other effects are smaller, take longer and do not happen for every man.
- First weeks to months: libido, and sometimes energy and mood.
- Over several months: modest gains in lean mass and losses of body fat, and correction of anemia caused by low testosterone.
- Over a year or more: improved bone density.
Erections may improve, but usually less than with standard erectile dysfunction medication. In trials of older men, effects on vitality and memory were small or absent. If symptoms have not improved after several months at a good level, doctors usually advise stopping.
What are the risks and side effects of testosterone replacement therapy?
The most common serious side effect is erythrocytosis, a rise in red blood cells that thickens the blood. It is more frequent with injections and is the main reason for regular blood counts.
- Infertility and testicular shrinkage: sperm counts fall, sometimes to zero. Recovery after stopping can take many months and is not guaranteed.
- Skin and breast effects: acne, oily skin, breast tenderness or enlargement.
- Sleep apnea: treatment may worsen untreated apnea.
- Prostate: PSA often rises a little. Testosterone replacement therapy has not been shown to cause prostate cancer, but monitoring is standard. See our PSA test guide.
On heart safety, a large 2023 trial called TRAVERSE found that TRT did not raise the rate of major cardiac events in the men studied, who had low testosterone and heart disease or high risk of it. The same trial reported more atrial fibrillation and kidney injury in the testosterone group, so heart and kidney history still matters.
How is TRT monitored?
TRT is monitored with blood tests for testosterone, hematocrit and PSA, plus a symptom review at each visit. Checks are closest in the first year and then usually yearly.
| Check | When | Why |
|---|---|---|
| Testosterone level | A few months after starting or changing dose, then yearly | To keep levels in the mid-normal range |
| Hematocrit | Before starting, at 3 to 6 months, then yearly | Above 54%, treatment is paused or the dose reduced |
| PSA | Before starting and in the first year, then as for prostate screening | A marked rise needs a urology review |
A clinic that prescribes without baseline tests or skips follow-up blood work is not following guidelines.
What does TRT cost, and are telehealth clinics safe?
Cost varies widely by form: generic injections are usually the cheapest, while brand-name gels, oral capsules and pellets cost much more. Insurance often covers treatment only when two low morning tests are documented.
Telehealth clinics can be legitimate, but their quality varies. Be cautious if a clinic:
- prescribes after one test, an afternoon test or no test
- treats men with normal levels, or aims for levels above the normal range
- does not ask about fertility plans
- has no plan for hematocrit and PSA monitoring
We list more warning signs in TRT clinic red flags.
What are the alternatives to TRT?
The main alternative is to treat the cause of low testosterone, and for many men that means losing excess weight. Other options depend on your goals.
- Lifestyle: weight loss, exercise, better sleep and less alcohol. See natural ways to boost testosterone after 40.
- Treating related conditions: sleep apnea, type 2 diabetes and depression.
- Medication review: opioids and steroid tablets can lower testosterone.
- Fertility-preserving drugs: specialists sometimes use clomiphene (off-label) or hCG for men who want children.
- Erectile dysfunction medication: compare options in Viagra vs Cialis vs Levitra.
When should you see a doctor?
See a doctor before starting testosterone from any source, and contact your prescriber promptly if problems appear during treatment. Red flags on TRT include:
- chest pain, palpitations or sudden breathlessness (call emergency services)
- a painful, swollen calf, which can signal a blood clot
- sudden weakness, speech difficulty or loss of vision
- new or worse urinary symptoms, or blood in the urine
- a breast lump, or breast growth that persists
- loud snoring with pauses in breathing
- ankle swelling or rapid weight gain
Testosterone replacement therapy FAQ
What is testosterone replacement therapy?
Testosterone replacement therapy is prescription testosterone given to men whose bodies make too little. It comes as injections, gels, patches, pellets, capsules or nasal gel, and aims to restore levels to the normal range.
What testosterone level qualifies for TRT?
Guidelines commonly use a total testosterone below about 300 ng/dL on two early-morning blood tests taken on different days. Symptoms of deficiency must also be present. A single low result is not enough.
How long does TRT take to work?
Sex drive often improves within the first weeks to months. Changes in muscle and body fat take several months, and bone density takes a year or more. Not every man notices a benefit.
Does TRT cause infertility?
It can. Testosterone from outside the body switches off the signals that drive sperm production, and counts may fall to zero. Fertility usually returns after stopping, but recovery can take many months and is not guaranteed.
Is testosterone replacement therapy safe for the heart?
A large 2023 trial found no increase in major cardiac events in the men studied. It did report more atrial fibrillation and kidney injury, so men with heart or kidney disease need an individual assessment.
Does TRT cause prostate cancer?
Studies have not shown that testosterone replacement therapy causes prostate cancer. PSA often rises slightly on treatment, so doctors check it before starting and during follow-up. Men with untreated prostate cancer should not take it.
Is TRT for life?
Often, yes. If the cause of low testosterone is permanent, levels fall again when treatment stops. Men whose low levels were due to obesity or a medicine may be able to stop once that is addressed.
Can I get TRT if my testosterone is normal?
Guidelines advise against it. Testosterone replacement therapy has not been shown to help men with normal levels, and it still carries risks such as infertility and thicker blood. Other causes of symptoms should be checked.
Bottom line
Testosterone replacement therapy is a reasonable treatment for men with symptoms and confirmed low levels, and a poor choice for men with normal levels or plans for children. Expect the clearest gains in sex drive and more modest ones elsewhere. Choose a prescriber who tests twice, discusses fertility and monitors hematocrit and PSA.
References
- Endocrine Society: Testosterone Therapy in Men With Hypogonadism, clinical practice guideline.
- American Urological Association: Clinical guidelines, including Testosterone Deficiency.
- MedlinePlus: Testosterone Levels Test.
- MedlinePlus: Male Infertility.
- MedlinePlus: Sleep Apnea.
This article is for information only and is not medical advice. Supplements are not intended to diagnose, treat, cure or prevent any disease.