Finasteride is a medication commonly prescribed to address conditions related to the male hormone system. It treats male pattern baldness (androgenetic alopecia) at a 1 milligram dose, and benign prostatic hyperplasia (enlargement of the prostate gland) at a higher 5 milligram dose. A potential side effect is gynecomastia, defined as the non-cancerous enlargement of glandular breast tissue in men. This enlargement results from a shift in the balance between androgen and estrogen hormones.
Clinical Evidence of Risk
Clinical trials have established that finasteride is associated with a small increase in the likelihood of developing gynecomastia compared to a placebo. For men taking the higher 5 milligram dose, the risk was approximately two times greater than in the placebo group. The reported incidence for the higher dosage was around 3.30% of users, contrasting with a rate of about 1.84% in men taking an inactive substance.
For the lower 1 milligram dose, the incidence is considered very low. Initial large-scale studies did not list gynecomastia as a side effect, but post-marketing surveillance confirmed the association, leading to its inclusion on the drug’s label. Data suggest a risk range of approximately 1% to 2% for the low-dose formulation. Despite this known complication, the overall occurrence of finasteride-related gynecomastia remains uncommon for both dosages.
The Hormonal Changes That Lead to Gynecomastia
The mechanism by which finasteride leads to breast tissue growth is directly related to its function of hormone manipulation. Finasteride is classified as a 5-alpha reductase inhibitor, blocking the action of the 5-alpha reductase enzyme. This enzyme converts the androgen testosterone into the more potent androgen dihydrotestosterone (DHT).
By inhibiting this conversion, finasteride significantly reduces the body’s circulating levels of DHT. The body compensates by accumulating testosterone, which remains in the bloodstream at higher concentrations. This increased testosterone provides more substrate for the aromatase enzyme, which is present in various peripheral tissues, including fat cells and breast tissue.
The aromatase enzyme converts the excess testosterone into estradiol, a form of estrogen. Even a modest increase in the ratio of estrogen relative to androgens can stimulate the proliferation of glandular tissue within the male breast. This hormonal shift ultimately drives the development of gynecomastia in susceptible individuals.
Recognizing Symptoms and Next Steps
Finasteride-related gynecomastia usually begins with noticeable changes in the chest area. Men may detect a firm, rubbery lump or mass concentrated beneath the nipple and areola. This tissue may also be accompanied by tenderness, swelling, or pain in one or both breasts.
If these signs appear, consult with a healthcare provider immediately rather than abruptly stopping the medication. Timely evaluation allows a professional to confirm the diagnosis and rule out other causes of breast enlargement. The first line of management often involves discontinuing finasteride, which can lead to the spontaneous regression of the breast tissue in many cases.
The tissue may not always resolve completely, especially if the condition has been present for a longer duration, leading to the formation of fibrous tissue. For persistent or severe cases, medical treatments like selective estrogen receptor modulators may be considered to reduce the tissue size. When non-surgical methods fail to achieve satisfactory results, surgical intervention, such as a localized mastectomy, remains the most definitive option for permanent removal.