TLDR A man's breast enlargement from low-dose finasteride for hair loss didn't go away, even with treatment, and might be more common than reported.
The document discusses a case of a 20-year-old man who developed persistent gynecomastia (enlargement of a man's breasts) after taking a low-dose of finasteride for one month to treat androgenetic alopecia (hair loss). Despite discontinuing the drug and undergoing treatment with raloxifene, the gynecomastia did not fully resolve, leading to surgical intervention. The document also reviews 9 reported cases of gynecomastia due to low-dose finasteride, with 38% of these cases resulting in persistent gynecomastia. The document suggests that this side effect may be underreported and emphasizes the importance of patient education about this risk. It recommends immediate intervention with a Selective Estrogen Receptor Modulator (SERM) if gynecomastia develops during therapy to prevent irreversible effects.
1 citations,
April 2019 in “Clinical Breast Cancer” Medicines for enlarged prostate may raise the risk of breast growth and tenderness but not breast cancer.
38 citations,
October 2014 in “Current Opinion in Endocrinology, Diabetes and Obesity” 5-alpha reductase deficiency leads to male sexual development issues and treatments like finasteride help with prostate enlargement and hair loss.
45 citations,
August 2010 in “Hormone Molecular Biology and Clinical Investigation” Type 3 5α-reductase is more common and finasteride and dutasteride strongly inhibit it.
29 citations,
January 2009 in “International Journal of Trichology” Finasteride for hair loss may cause gynecomastia; doctors should inform patients.
195 citations,
February 2007 in “The Journal of Clinical Endocrinology and Metabolism” Dutasteride and finasteride may reduce sperm count and volume but don't affect movement or shape; effects are reversible after stopping.
30 citations,
March 2001 in “Archives of Dermatology” Finasteride can cause one-sided breast enlargement, which disappears after stopping the drug.
7 citations,
April 2000 in “Archives of Pathology & Laboratory Medicine” 
65 citations,
October 1999 in “Journal of The American Academy of Dermatology” Finasteride effectively reduces hair loss by decreasing androgen levels.
3 citations,
September 2019 in “American Journal of Men's Health” Finasteride may not affect gynecomastia recurrence after mastectomy.
2 citations,
January 2003 in “Journal of Clinical Dermatology” 26 citations,
April 2002 in “Archives of Dermatology” 
15 citations,
June 1995 in “The American Journal of the Medical Sciences” Finasteride caused enlarged breast tissue in a 62-year-old man.
