Testosterone replacement therapy
Real medicine for a real condition — and the wrong answer for most people who ask about it
Our overall score
Written by J. Porter, MPH
Medically reviewed by A. Vance, MD
Last reviewed
The short version
Testosterone therapy is effective, well-evidenced treatment for genuine hypogonadism. It is not an ED drug. Testosterone governs desire far more than it governs the mechanics of an erection, and if your levels are normal, replacing them will not fix erectile dysfunction. An entire industry is built on blurring that distinction, and on not mentioning that TRT suppresses fertility and is difficult to stop.
Our verdict: Legitimate and often life-changing for the narrow group who genuinely need it. For everyone else it is an expensive, semi-permanent commitment that treats the wrong problem. Get two morning blood tests before anyone prescribes you anything, and do not start if you might want children.
Best for: Men with symptomatic, laboratory-confirmed low testosterone — particularly where low desire, not erection mechanics, is the main complaint.
What works
- Genuinely effective for confirmed hypogonadism, often dramatically so
- Restores libido, energy, mood, and muscle mass when testosterone is truly deficient
- Can rescue PDE5 inhibitor non-response in men who are actually hypogonadal
- Generic injectable forms are inexpensive
- Large recent trial data has been reassuring on cardiovascular safety
What to watch
- Does not treat erectile dysfunction in men whose testosterone is normal
- Suppresses sperm production, sometimes irreversibly — a frequently undisclosed consequence
- Effectively a lifelong commitment; stopping causes a crash and recovery is not guaranteed
- Raises haematocrit, requiring ongoing blood monitoring
- Topical gels can transfer testosterone to partners and children by skin contact
- The direct-to-consumer 'low T' industry routinely diagnoses it too readily
At a glance
- How it works
- Supplies testosterone from outside the body to restore levels in men whose own production is deficient. It acts mainly on sexual desire, energy, mood, and muscle mass rather than directly on the blood-flow mechanics of an erection.
- Time to effect
- Libido and energy often shift within 3–6 weeks; erectile changes, where they occur, take 3–6 months
- Safety limit
- Suppresses sperm production — do not start if you may want children
- How you get it
- Prescription only; diagnosis requires two separate morning blood tests, not symptoms alone
- Regulatory status
- FDA-approved for classical hypogonadism due to established testicular or pituitary disease. Not approved as a treatment for erectile dysfunction, and not approved for age-related low testosterone alone
- Typical cost
- Generic injections are inexpensive; gels, pellets, and oral forms cost substantially more, plus ongoing lab monitoring
- Ongoing cost
- Indefinite, and stopping is not straightforward once your own production is suppressed
- Clinical standing
- AUA and Endocrine Society guidance supports treating confirmed symptomatic hypogonadism, and advises against prescribing testosterone for erectile dysfunction in men with normal levels
The distinction everything else depends on
Testosterone and erections are related, but not in the way the advertising implies.
Testosterone is the principal driver of sexual desire. It also supports the tissue and signalling that make erections possible. What it does not do is control the blood-flow event itself. That is the domain of nitric oxide, cGMP, and the vascular machinery a PDE5 inhibitor acts on.
This is why guidance from both the AUA and the Endocrine Society advises against prescribing testosterone for erectile dysfunction in men whose levels are normal. It is not a matter of caution. It simply does not work for that.
How low testosterone is actually diagnosed
Properly, and not from a questionnaire.
- 1Two separate blood tests, on different days. A single result is not enough — testosterone fluctuates substantially.
- 2Taken in the morning, generally before about 10am. Testosterone follows a daily rhythm and peaks early; an afternoon draw can look low in a man who is entirely normal.
- 3Total testosterone, with free testosterone where binding-protein abnormalities are suspected.
- 4Plus LH and FSH, which distinguish a testicular problem from a pituitary one — different causes, different treatment.
- 5Plus prolactin, because a pituitary tumour is a rare but important cause you do not want to miss by simply topping up testosterone.
- 6Plus baseline haematocrit and PSA, because both need monitoring once treatment starts.
A commonly used threshold for total testosterone is around 300 ng/dL, but the number matters less than the combination: levels genuinely below the reference range, on two morning tests, together with symptoms. Low numbers without symptoms, or symptoms without low numbers, do not add up to a diagnosis.
The consequence nobody mentions in the advert
There are alternatives that raise testosterone without suppressing fertility — clomiphene, hCG, and related approaches that work by stimulating your own production rather than replacing it. They are used off-label and are not right for everyone, but a prescriber who never raises them when fertility is on the table is not doing the job properly.
Sperm banking before starting is worth discussing even if you are unsure. It is far cheaper than discovering the problem later.
The other thing nobody mentions: it is hard to stop
Once you supply testosterone externally, your own production winds down. Stop the treatment and you land below where you started, sometimes for months, while the system restarts — if it fully does.
That makes TRT closer to a permanent commitment than a trial. Anyone selling it as something you can casually try for a few months to see how you feel is either not thinking it through or not telling you.
The formulations
| Form | Schedule | Trade-offs |
|---|---|---|
| Injections (cypionate/enanthate) | Weekly or fortnightly | Cheapest by far. Peaks and troughs can make mood and energy fluctuate; weekly or smaller subcutaneous doses smooth this out |
| Topical gel | Daily | Steady levels, no needles. Carries a genuine risk of transferring testosterone to partners and children through skin contact |
| Patch | Daily | Steady levels; skin irritation is common enough to be a frequent reason for stopping |
| Pellets | Implanted every 3–6 months | Nothing to remember. Requires a minor procedure, and the dose cannot be adjusted once implanted |
| Nasal gel | Several times daily | May affect sperm production less than other routes. The dosing frequency defeats many people |
| Oral (testosterone undecanoate) | Twice daily with food | Newer formulations avoid the liver toxicity of older oral androgens. Expensive, and must be taken with fat to absorb |
The risks worth knowing
- Raised haematocrit — testosterone thickens the blood, raising clot risk. This needs monitoring, and treatment is paused or reduced if it climbs too high. It is the most common reason for dose adjustment.
- Fertility suppression — covered above, and the most consequential.
- Testicular shrinkage, from the same suppression.
- Breast tenderness or enlargement, as some testosterone converts to oestradiol.
- Worsening of sleep apnoea, which is worth asking about if you snore heavily or wake unrefreshed.
- Acne and oily skin, particularly early on.
- Prostate monitoring — testosterone is not thought to cause prostate cancer, but it is contraindicated in active untreated prostate cancer, and PSA is usually tracked.
The cardiovascular question
This has been genuinely contested. Earlier observational work suggested testosterone therapy might raise cardiovascular risk, and the FDA added a label warning on that basis.
The picture improved substantially with the TRAVERSE trial, a large randomised study in men with hypogonadism and elevated cardiovascular risk, which found testosterone replacement non-inferior to placebo for major adverse cardiac events. That was a meaningful reassurance on the central question.
It was not a clean sweep. The same trial recorded numerically higher rates of atrial fibrillation, pulmonary embolism, and acute kidney injury in the testosterone group. The reasonable summary is that TRT does not appear to cause heart attacks, and is not risk-free either — which is an argument for proper monitoring, not for avoidance.
When testosterone genuinely helps erections
There is one scenario where the two subjects legitimately meet, and it is worth knowing because it is specific.
Some men who are actually hypogonadal and who get no useful response from PDE5 inhibitors become responsive once testosterone is corrected. The testosterone does not produce the erection; it restores the conditions in which the medication can work.
How the 'low T' clinic model works
The direct-to-consumer testosterone market has the same structural incentive as the rest of this site's subject matter, only sharper: it sells an indefinite subscription to a treatment that is difficult to stop, to a population screened by the seller.
- Diagnosis on one test, or on a symptom questionnaire alone
- Treating men inside the normal range, on the argument that they could feel 'optimised'
- Marketing it for ED, energy, or 'vitality' rather than for hypogonadism
- Silence on fertility until after you have started
- No mention that stopping is difficult
- Monthly membership pricing that continues regardless of whether you are benefiting
- Bundled add-ons — other injectables, peptides, supplements — with thinner evidence than the testosterone
None of this means testosterone therapy is a scam. It means the people most eager to sell it to you are frequently not the people best placed to tell you whether you need it. If low testosterone is a real possibility, that is a reason to see someone who has no financial stake in the answer — see telehealth or your own doctor.
Before you consider it at all
Low testosterone is sometimes the consequence of something else, and correcting that something else can raise it without any prescription at all. Worth ruling out first:
- Obesity, which lowers testosterone through several mechanisms and responds to weight loss
- Untreated obstructive sleep apnoea
- Chronic opioid use, a common and reversible cause of suppression
- Anabolic steroid use, past or present
- Excess alcohol
- Poorly controlled diabetes or thyroid disease
- Pituitary problems, which is what the prolactin test is for
Common questions
Will testosterone fix my erectile dysfunction?
Almost certainly not, unless your testosterone is genuinely low. Testosterone governs sexual desire much more than the mechanics of an erection. Both AUA and Endocrine Society guidance advise against prescribing it for ED in men with normal levels. If desire has faded alongside the erections, that is the pattern worth testing for.
How do I know if my testosterone is actually low?
Two separate blood tests taken in the morning, generally before 10am, showing levels below the reference range — together with symptoms. A commonly used threshold is around 300 ng/dL. A single afternoon draw is not a diagnosis, and neither is a symptom questionnaire.
Does TRT make you infertile?
It suppresses sperm production, frequently to the point of azoospermia, and recovery after stopping can take a year or more and is not guaranteed. This is the most important consequence to settle before starting. If fertility matters, ask about clomiphene or hCG, which raise testosterone by stimulating your own production instead of replacing it.
Can I stop taking it later?
You can, but it is not a clean exit. External testosterone suppresses your own production, so stopping typically drops you below your original baseline for a period while the system restarts — and full recovery is not certain. Treat it as a long-term commitment rather than a trial.
Is testosterone therapy bad for your heart?
The large TRAVERSE trial found testosterone replacement non-inferior to placebo for major adverse cardiac events in men with hypogonadism and high cardiovascular risk, which was reassuring on the main question. The same trial did record more atrial fibrillation, pulmonary embolism, and acute kidney injury in the testosterone group, so monitoring still matters.
What's the difference between TRT and steroids?
Dose and intent. TRT aims to restore a normal physiological level in someone deficient. Anabolic steroid use involves supraphysiological doses to build muscle beyond normal, with a correspondingly different risk profile. The drugs can overlap; the practice does not.
Are the clinics advertising testosterone legitimate?
Some are. The warning signs are diagnosis from a single test or a questionnaire, treating men whose levels are normal, marketing it as an ED or vitality treatment, and not raising fertility until after you have started. If any of those apply, get a second opinion from someone who is not selling the prescription.
Sources
- 1.Erectile Dysfunction: AUA Guideline — American Urological Association
- 2.Testosterone Deficiency Guideline — American Urological Association
- 3.Testosterone Therapy in Men With Hypogonadism — Clinical Practice Guideline — The Endocrine Society
- 4.Testosterone products: FDA labeling changes and safety communications — U.S. Food and Drug Administration