The causes, roughly in order of how often they turn up
| Cause | Share of cases | Who it affects |
|---|---|---|
| Puberty and other normal hormone shifts | About 1 in 4 | Teenagers, newborns, men over 50 |
| No cause found (idiopathic) | About 1 in 4 | Any age |
| Medicines, steroids and other substances | 1 in 10 to 1 in 4 | Any age, especially gym users and men on long-term medicines |
| Liver disease (cirrhosis) | About 1 in 12 | Often linked to heavy drinking |
| Low testosterone (hypogonadism) | About 1 in 10 altogether | Testicle problems, pituitary problems, some genetic conditions |
| Overactive thyroid | About 1 in 50 | Weight loss, a fast heartbeat, feeling hot |
| Kidney failure | About 1 in 100 | Men on dialysis |
| Tumours that make hormones | About 3 in 100 | Rare, but the reason adults get checked |
The shares come from a large review of men seen by doctors for gynaecomastia. Being overweight runs through many of these, and it makes the chest look bigger on its own.
Puberty
The most common cause of all. Hormones swing during puberty, and for a while oestrogen can run ahead of testosterone. About half of boys get some breast tissue, usually starting around 13 or 14. It usually settles within six months to two years. Our teenage guide is written for boys and their parents.
Weight
Fat tissue turns some testosterone into oestrogen, so the more body fat a man carries, the more oestrogen he makes. That can grow real gland tissue, and the fat on the chest adds to the size. Losing weight helps both, but it won't remove a firm disc of gland once it has set.
Medicines
A long list of medicines can cause gynaecomastia. The ones doctors see most often:
- spironolactone (a water tablet used for the heart and blood pressure)
- medicines for prostate cancer that block or lower testosterone
- finasteride and dutasteride (used for an enlarged prostate and for hair loss)
- digoxin (a heart medicine)
- some stomach acid medicines, such as cimetidine
- ketoconazole (an antifungal) and some HIV medicines
- some medicines for mental health, and some chemotherapy
- testosterone itself, and other hormones, when the dose or the balance is off
Never stop a prescribed medicine on your own. Ask the doctor who prescribed it whether it could be the cause and whether there is an alternative. Breast tissue that appeared after starting a medicine often goes down within months of changing it.
Anabolic steroids, SARMs and prohormones
Steroids are one of the most common causes in young men who train. Extra testosterone gets converted to oestrogen, and when a cycle stops, the body's own testosterone takes weeks or months to recover, leaving oestrogen in charge. We have a separate guide on steroids.
Alcohol and cannabis
Heavy drinking can cause gynaecomastia directly and through liver damage, which stops the liver breaking down oestrogen. Cannabis has also been linked to it. Cutting back is worth trying before anything else.
Getting older
Testosterone falls slowly from middle age while body fat tends to rise, so gynaecomastia becomes common again after 50. Older men also take more of the medicines on the list above. See our guide for men over 50.
Illness
An overactive thyroid, liver or kidney disease, problems with the testicles or the pituitary gland, and rarely a tumour that makes hormones can all cause it. These are uncommon, but they are why an adult with new breast tissue should see a GP. Our GP and tests guide explains what they check.
Questions people ask
Can stress cause gynaecomastia?
Not directly. Stress can change weight, sleep, drinking and medicines, and those can play a part. There's no good evidence that stress on its own grows breast tissue.
Can soy or protein shakes cause gynaecomastia?
Normal amounts of soy food don't cause it in healthy men. The real worry with gym supplements is products that contain hidden steroids or prohormones. If a supplement promises steroid-like gains, treat it as a steroid.
Can gynaecomastia come back?
If the cause comes back, so can the tissue. Steroids, weight gain and some medicines can regrow it, even after surgery.
Why do I have it when none of my friends do?
Gynecomastia is far more common than it looks, because men hide it. About a quarter of cases have no cause anyone can find.