What the regulator says
The Propecia 1 mg SmPC lists 'breast tenderness and enlargement' as an undesirable effect with frequency 'not known' (it cannot be estimated from the available data), and lists male breast cancer among reports from post-marketing use. Section 4.4 states: 'Breast cancer has been reported in men taking finasteride 1 mg during the post-marketing period. Physicians should instruct their patients to promptly report any changes in their breast tissue such as lumps, pain, gynaecomastia or nipple discharge.' Separately, the MHRA Drug Safety Updates of 29 April 2024 and 11 May 2026 cover the risk of psychiatric reactions including depression and suicidal thoughts, and of sexual dysfunction (reduced libido, erectile dysfunction, ejaculatory disorders) which may persist after discontinuation. Patient alert cards are now included in finasteride packs.
In plain English
Finasteride works by lowering DHT, a male hormone. Breast tenderness and breast enlargement are listed side effects. In practice that can mean sore or sensitive nipples, or a small swelling of breast tissue behind the nipple. Enlarged breast tissue in men is called gynaecomastia. The NHS describes it as common and often harmless, with several possible causes: hormone changes with age, excess weight, certain medicines, thyroid or kidney conditions, and steroid misuse.
The UK product information gives the frequency as 'not known', which means reports exist but the data cannot give a reliable rate. Breast cancer has also been reported in men taking finasteride. That does not show finasteride causes it. The reports are the reason the SmPC asks men to report breast changes promptly, so that anything needing a check gets one. For context, the UK SmPC for dutasteride, a related medicine, states that epidemiological studies showed no increase in the risk of male breast cancer with the use of 5-alpha-reductase inhibitors.
Breast changes in men often have causes other than cancer, but a new lump should always be examined.
How long does it last
The product information does not say how long finasteride-related breast changes last. If finasteride is thought to be the cause, your prescriber may advise stopping it. For gynaecomastia that persists, NHS treatment options include treating any underlying cause, medicines that change hormone levels and, in some cases, surgery.
What to do if it happens to you
Report any breast change to your prescriber promptly. This is what the SmPC asks for: lumps, pain, breast enlargement or nipple discharge. Note which side, when you first noticed it, and whether it is tender, growing or changing.
See your GP if you find a lump or swelling in your chest or armpit, have discharge from either nipple, or notice any change in your chest or nipples that is not normal for you. These are the NHS reasons to see a GP about possible breast cancer in men. Do not wait to see whether it settles.
Decide with your prescriber whether to continue. Choosing to stop is always a valid decision; our guide to stopping finasteride safely explains what to expect for your hair. Our finasteride 1 mg page and the MHRA safety updates set out the other warnings you should know about.
Report it on the Yellow Card scheme. Breast changes are a recognised but poorly quantified side effect, so each Yellow Card report helps the MHRA build a clearer picture.
Also tell your prescriber straight away about any low mood, anxiety or sexual problems, which are covered by the MHRA warnings (see finasteride and depression). If you are having thoughts of suicide, call Samaritans on 116 123 (free, 24/7) or NHS 111.
Want bloods to help investigate?
If you would like a bloodwork baseline to support the clinical conversation about your symptoms, our sister diagnostic service WMG Health offers panels designed around the question you are asking. A clinician-designed custom panel (from £275) is usually the best route when the question is specific.
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