Testosterone Replacement Therapy and Gynaecomastia: Why It Happens and What It Means for Surgery

Testosterone replacement therapy (TRT) can cause gynaecomastia because some of the testosterone is converted into oestrogen in the body, and when oestrogen builds up the male breast gland can grow. It is a recognised side effect of a prescribed treatment, which means the first person to talk to is the doctor who prescribes it, and surgery is usually the last step rather than the first¹.

I was never on testosterone; my chest was a different story, set out in the years I spent hiding my chest. But “I’m on TRT and my chest is changing” is one of the questions that arrives most often in our members’ room, and it usually comes with a misunderstanding attached: either that this is the same as steroid gyno and the answer is to stop, or that it is a cosmetic problem that goes straight to a surgeon. Neither is quite right. This is the explanation, with the clinical lines checked by our reviewer.

Why does testosterone cause breast tissue to grow?

Gynaecomastia develops when the balance between oestrogen and androgen activity in the breast tilts toward oestrogen, and on TRT that happens because testosterone is partly converted into oestrogen in fat and other tissues. More testosterone in means more raw material for that conversion, so if the conversion runs high, oestrogen rises alongside it¹.

That sounds backwards until you see it as a ratio rather than a quantity. The male breast responds to the balance of the two hormones, not to how much testosterone is in the blood. A 2025 review of TRT side effects describes gynaecomastia being observed when high levels of oestrogen build up in men receiving testosterone, and lists ways prescribers bring that back down¹. The same ratio explains why gynaecomastia turns up at puberty and in older age; the general picture is in what causes gynaecomastia.

The other half of the story is the reason TRT was started. Low testosterone itself is listed among the causes of gynaecomastia, and men over 50 are more likely to have it and more likely to take medicines that can cause it as well². So a man on TRT with a fuller chest may have had some of it before the prescription began, which is worth knowing before blaming the treatment for all of it.

TRT is not the same as steroid gyno

The mechanism overlaps with anabolic steroid gynaecomastia, but the situation is different: TRT is a prescribed, monitored treatment at replacement doses, while steroid misuse is unsupervised and often at much higher doses. That changes the first step completely.

With steroids, the advice on this site and from surgeons is plain: use has to stop and the chest has to be stable before surgery, because operating on a chest that is still being stimulated is a common route to it coming back. That reasoning is set out in steroids and gynaecomastia. With TRT, stopping is not your call to make. You are on it for a reason, a doctor is monitoring it, and stopping a prescribed hormone suddenly has its own effects. The move is to tell the prescriber what you have noticed and let them look at the numbers.

The NHS lists both certain medicines and anabolic steroid use among the causes of gynaecomastia, and Cleveland Clinic is equally plain that you should never stop taking a prescription medication without your provider’s guidance³².

What can be done about it without surgery?

Prescribers have several levers before surgery: checking blood levels, lowering the dose or switching to a formulation that converts less to oestrogen, and in some cases a medicine that lowers oestrogen or blocks its effect on breast tissue. The 2025 review describes dose adjustment and switching to less aromatising formulations, the use of aromatase inhibitors such as anastrozole when oestrogen is raised, and low-dose tamoxifen for symptomatic breast enlargement¹.

Which of those suits you is a prescribing decision that depends on your blood results, why you are on TRT, and the rest of your health. It is not something to sort out from a forum or by buying tablets online, and I would be wary of anyone who sells you an oestrogen blocker without the blood tests to show you need one. The review also notes that a wait-and-observe approach may be reasonable where the chest changes without raised oestrogen¹.

Timing matters here in a way men are rarely told. New, tender breast tissue is the most responsive stage. Gland that has sat there for a long time tends to become firmer and less likely to shrink back with any hormonal adjustment, which is the point at which the conversation moves from the prescriber’s desk to a surgeon’s. That firm, established disc is the same tissue described in gynaecomastia versus pseudogynaecomastia.

When does surgery come into it?

Surgery is usually considered once the hormonal side has been addressed, the chest has been stable for a period, and the tissue has not settled; the 2025 review suggests elective surgery could be considered after at least 12 months of observation in men with normal oestrogen levels. That timeline is a guide, not a rule, and your surgeon and prescriber will set it for you¹.

When it does come to an operation, the same principles apply as for any true gynaecomastia. The firm gland behind the nipple has to be excised, not just the fat around it liposuctioned. Liposuction alone can leave the gland behind, and under-resection and revision both appear among the complications recorded in a systematic review of more than 7,000 operations; a continuing hormonal driver makes the gland excision more important, not less⁴.

If you will stay on testosterone long term, say so at the consultation. A surgeon who knows the hormonal background can plan for it, and a prescriber who knows surgery is coming can make sure the levels are stable going in. In practice the two of them talking, or at least you carrying the blood results between them, is what protects the result.

Questions to take to your prescriber and your surgeon

Take the questions to the right person: hormone questions to the doctor who prescribes your testosterone, chest questions to a plastic surgeon, and any new lump to your GP first. Splitting them that way saves a lot of circular appointments.

For the prescriber:

• Are my oestrogen levels raised, and has anything changed since my last blood test?
• Would a different dose or formulation make a difference?
• Is there a medicine that would help the tenderness, and what are its own risks?
• How long would you want to watch this before we consider anything else?

For the surgeon:

• Is this gland, fat or both, and what grade would you call it?
• Will you excise the gland, or is the plan liposuction only?
• Does my staying on testosterone change your plan or the chance of it coming back?
• How long do you want my levels stable before you operate?

The broader consultation list is in questions to ask before gynaecomastia surgery.

When a lump needs checking first

A new lump, a lump on one side only that keeps growing, nipple discharge or bleeding, skin changes or pain that will not settle should be seen by a doctor before anyone talks about TRT side effects or surgery. The NHS lists each of these as reasons to see a GP³.

Most of the time, on TRT, the answer will be gynaecomastia, and a doctor examining you will be able to say so quickly. The point of the check is that the cause is confirmed rather than assumed. That rule runs through everything on this site and it does not relax because you know you are on a hormone that can cause it.

What I would say to a man on TRT reading this

If your chest is changing on testosterone, you are not doing anything wrong and you are not alone; it is a recognised effect that prescribers deal with routinely. Tell the doctor who prescribes it early, while the tissue is newest, rather than waiting a year out of embarrassment. If it settles, good. If it does not, and the gland has become established, surgery is a well-trodden route, done the same way as for any true gynaecomastia, with the gland removed. Whether your chest changes are from the testosterone, what to adjust and when surgery is right are decisions for your prescriber and a plastic surgeon who can examine you, not for a website.