Dutasteride side effects: what the label and studies actually report

Dutasteride blocks both type I and type II 5-alpha-reductase, the enzymes that convert testosterone into dihydrotestosterone (DHT). Its FDA-approved use is benign prostatic hyperplasia (BPH) at 0.5 mg once daily; for hair loss it is off-label in most countries, though Japan and South Korea have approved oral dutasteride 0.5 mg/day for male androgenetic alopecia (Gupta et al., 2022). This page summarises what the prescribing information and published trials report — and where they stop short of an answer.

One thing to hold onto while reading: almost all the frequency data comes from BPH trials in men aged 47 to 94, mean age 66. The hair-loss trials are younger but much shorter and smaller. Neither set alone describes a 28-year-old treating his hairline.

What the FDA label reports

The Avodart prescribing information (US label revised January 2020) lists the most common adverse reactions on dutasteride alone as impotence, decreased libido, breast disorders (enlargement and tenderness), and ejaculation disorders. Its Table 1 pools three 2-year placebo-controlled trials in over 4,300 men, by time of onset:

Adverse reaction	Months 0-6	Months 7-12	Months 13-18	Months 19-24
Impotence — dutasteride	4.7%	1.4%	1.0%	0.8%
Impotence — placebo	1.7%	1.5%	0.5%	0.9%
Decreased libido — dutasteride	3.0%	0.7%	0.3%	0.3%
Decreased libido — placebo	1.4%	0.6%	0.2%	0.1%
Ejaculation disorders — dutasteride	1.4%	0.5%	0.5%	0.1%
Ejaculation disorders — placebo	0.5%	0.3%	0.1%	0.0%
Breast disorders — dutasteride	0.5%	0.8%	1.1%	0.6%
Breast disorders — placebo	0.2%	0.3%	0.3%	0.1%

Two details matter. The placebo column is not zero — some of what men report on any drug is reported on a dummy capsule too. And the gap between drug and placebo is widest in the first six months, then largely closes; the label states that across the three 4-year pivotal trials there was "no evidence of increased sexual adverse reactions... or breast disorders with increased duration of treatment". That describes new reports over time. It is not a promise that an individual's symptoms will settle. The label also reports that 4% of men on dutasteride withdrew because of adverse reactions versus 3% on placebo, most often for impotence (1%).

What the hair-loss trials report

Eun and colleagues randomised 153 Korean men aged 18 to 49 to dutasteride 0.5 mg or placebo for six months, and reported "no major difference in adverse events between the two groups" — noting the six-month limit (Eun et al., 2010). Gubelin Harcha and colleagues randomised 917 men aged 20 to 50 across dutasteride doses, finasteride 1 mg and placebo for 24 weeks, and reported that "the number and severity of adverse events were similar among treatment groups" (Gubelin Harcha et al., 2014). Choi and colleagues reviewed 99 Korean men treated at one hospital for at least five years and reported sustained efficacy and safety over that period (Choi et al., 2024) — a retrospective chart review, not a randomised safety comparison, and too few men to detect uncommon events.

So the hair-loss evidence is short, small, and reports adverse-event counts similar to the comparator arms. It was not designed or powered to establish long-term rates in younger men.

Dutasteride versus finasteride

Zhou and colleagues pooled three randomised trials in 576 men over 24 weeks. Dutasteride came out ahead on hair count, but on safety they found no significant difference from finasteride for altered libido (P = 0.54), erectile dysfunction (P = 0.07) or ejaculation disorders (P = 0.58), concluding the two "appear to show similar rates of adverse reactions" (Zhou et al., 2019). A network meta-analysis by Gupta and Charrette likewise found the active treatments not significantly different from each other, nor from placebo, in eliciting sexual dysfunction (Gupta & Charrette, 2014). In trials this short, "not significantly different" means the data cannot separate them — not that no difference exists.

Do the effects go away?

Dutasteride has a terminal elimination half-life of about five weeks at steady state, and the label notes serum levels stay detectable for four to six months after the last dose. Anything driven by DHT suppression washes out over months, not days.

Whether some effects outlast the drug is contested. The label footnotes its own sexual adverse-reaction rows: these reactions "may persist after treatment discontinuation. The role of dutasteride in this persistence is unknown." For finasteride, the FDA approved a Propecia label revision on 11 April 2012 adding to postmarketing experience "sexual dysfunction that continued after discontinuation of treatment, including erectile dysfunction, libido disorders, ejaculation disorders, and orgasm disorders". Postmarketing reports are voluntary, come from a population of unknown size, and cannot establish frequency or causation — the labels say so themselves. The reports exist and regulators have put them in writing; how often this happens, and whether the drug causes it, is not established. Neither dismissing them nor treating them as a measured rate is supported by what has been published.

Mood

Garcia-Argibay and colleagues followed 2,236,876 Swedish men aged 50 to 90 and reported a higher risk of a depression diagnosis on 5-alpha-reductase inhibitors: hazard ratio 1.68 (95% CI 1.43-1.96) for dutasteride and 1.61 (95% CI 1.48-1.75) for finasteride, with no association with completed suicide (dutasteride HR 0.98, 95% CI 0.62-1.54). The depression signal stayed constant over time (Garcia-Argibay et al., 2022). Welk and colleagues, in 93,197 Ontario men aged 66 or older, reported increased self-harm (HR 1.88) and depression (HR 1.94) in the first 18 months, no increase in suicide, and an absolute increase of 237 depression events per 100,000 patient-years (Welk et al., 2017). Both are observational studies in older men: association, not cause. The Avodart label lists "depressed mood" under postmarketing experience.

PSA and prostate screening

Not a side effect, but the safety point most easily missed. The label states dutasteride reduces serum PSA by roughly 50% within three to six months. Clinicians are told to set a new PSA baseline at least three months after starting, and to double an isolated PSA value in a man treated for three months or more before comparing it with normal ranges; any confirmed rise from the lowest on-treatment value should be investigated even if it still looks normal. Anyone taking dutasteride must tell every clinician who orders a PSA test.

High-grade prostate cancer

In the 4-year REDUCE trial of 8,231 men aged 50 to 75 with a prior negative biopsy, Gleason 8-10 prostate cancer was found in 1.0% on dutasteride versus 0.5% on placebo, while overall biopsy-detected cancer fell by 22.8% (Andriole et al., 2010). The FDA added a warning on increased risk of high-grade prostate cancer to the Avodart label in June 2011. In plain terms: roughly one extra Gleason 8-10 tumour per 200 men biopsied over four years in a screened, higher-risk group, alongside fewer low-grade cancers. The label states it has not been established whether the drug causes this or whether shrinking the prostate simply made aggressive tumours easier to find on biopsy. Neither explanation has been ruled out.

Cardiac failure and other listed reactions

In CombAT the composite term cardiac failure occurred in 0.7% of the dutasteride-plus-tamsulosin group versus 0.1% on dutasteride alone and 0.6% on tamsulosin alone; in REDUCE it was 0.6% on dutasteride versus 0.4% on placebo (Roehrborn et al., 2010; Andriole et al., 2010). The label states most affected men had comorbidities, that the significance of the imbalance is unknown, that no causal relationship has been established, and that overall cardiovascular events were not imbalanced. Dizziness appears in the CombAT table (0.5% on dutasteride, months 0-6). Postmarketing reports on the label include hypersensitivity reactions with rash, urticaria, serious skin reactions and angioedema; testicular pain and swelling; and male breast cancer. The label also reports mean reductions in total sperm count, semen volume and motility at 52 weeks, with total sperm count not back to baseline 24 weeks after stopping, though group means stayed within the normal range and the significance for an individual's fertility is stated to be unknown.

Pregnancy, handling and blood donation

Dutasteride is contraindicated in pregnancy because it may harm a male fetus. The label states women who are pregnant or may be pregnant should not handle the capsules at all: dutasteride is absorbed through skin, and if a pregnant woman contacts a leaking capsule the area should be washed immediately with soap and water. Men taking dutasteride must not donate blood until at least six months after their last dose, specifically so the drug cannot reach a pregnant transfusion recipient.

User Experiences

These are self-reports from community forums, not study results, and nobody has counted them systematically. The recurring themes members describe are reduced libido or weaker erections in the early weeks — sometimes described as settling, sometimes as the reason they stopped; reduced semen volume; breast tenderness; and an initial shedding phase that posters usually say passed. A smaller group describes sexual or mood symptoms they say continued after stopping. Others report no change they attribute to the drug. Individual accounts cannot tell you how likely any of this is for you, and people who have a problem are more likely to post than people who do not.

Talk to a doctor

Dutasteride is a prescription-only medicine, used off-label for hair loss in most countries. Talk to a doctor or pharmacist before starting, stopping or combining dutasteride, and do not change your dose on your own. Report new or persistent sexual symptoms, breast lumps, tenderness or discharge, mood changes or thoughts of self-harm, and any rash or swelling of the face, lips or throat to your prescriber. Tell every clinician who might order a PSA test that you take it. Do not donate blood until at least six months after your last dose. Women who are or may become pregnant must not handle the capsules.

References

Andriole, G. L., Bostwick, D. G., Brawley, O. W., Gomella, L. G., Marberger, M., Montorsi, F., ... Rittmaster, R. S. (2010). Effect of dutasteride on the risk of prostate cancer. New England Journal of Medicine, 362(13), 1192-1202. PMID 20357281. https://pubmed.ncbi.nlm.nih.gov/20357281/

Choi, S., Kwon, S. H., Sim, W. Y., & Lew, B. L. (2024). Long-term efficacy and safety of dutasteride 0.5 mg in Korean men with androgenetic alopecia: 5-year data demonstrating clinical improvement with sustained efficacy. The Journal of Dermatology, 51(5), 684-690. PMID 38321615. https://pubmed.ncbi.nlm.nih.gov/38321615/

Eun, H. C., Kwon, O. S., Yeon, J. H., Shin, H. S., Kim, B. Y., Ro, B. I., ... Ji, J. H. (2010). Efficacy, safety, and tolerability of dutasteride 0.5 mg once daily in male patients with male pattern hair loss: A randomized, double-blind, placebo-controlled, phase III study. Journal of the American Academy of Dermatology, 63(2), 252-258. PMID 20605255. https://pubmed.ncbi.nlm.nih.gov/20605255/

Garcia-Argibay, M., Hiyoshi, A., Fall, K., & Montgomery, S. (2022). Association of 5-alpha-reductase inhibitors with dementia, depression, and suicide. JAMA Network Open, 5(12), e2248135. PMID 36547981. https://pubmed.ncbi.nlm.nih.gov/36547981/

GlaxoSmithKline. (2020, January). AVODART (dutasteride) soft gelatin capsules — US prescribing information (NDA 021319, supplement 32). U.S. Food and Drug Administration. https://www.accessdata.fda.gov/drugsatfda_docs/label/2020/021319s032lbl.pdf

GlaxoSmithKline. (2011, June). AVODART (dutasteride) soft gelatin capsules — US prescribing information (NDA 021319, supplements 23 and 25; adds section 5.2, Increased Risk of High-grade Prostate Cancer). U.S. Food and Drug Administration. https://www.accessdata.fda.gov/drugsatfda_docs/label/2011/021319s023s025lbl.pdf

Gubelin Harcha, W., Barboza Martinez, J., Tsai, T. F., Katsuoka, K., Kawashima, M., Tsuboi, R., ... Chetty, D. (2014). A randomized, active- and placebo-controlled study of the efficacy and safety of different doses of dutasteride versus placebo and finasteride in the treatment of male subjects with androgenetic alopecia. Journal of the American Academy of Dermatology, 70(3), 489-498.e3. PMID 24411083. https://pubmed.ncbi.nlm.nih.gov/24411083/

Gupta, A. K., & Charrette, A. (2014). The efficacy and safety of 5-alpha-reductase inhibitors in androgenetic alopecia: A network meta-analysis and benefit-risk assessment of finasteride and dutasteride. Journal of Dermatological Treatment, 25(2), 156-161. PMID 23768246. https://pubmed.ncbi.nlm.nih.gov/23768246/

Gupta, A. K., Talukder, M., & Williams, G. (2022). Comparison of oral minoxidil, finasteride, and dutasteride for treating androgenetic alopecia. Journal of Dermatological Treatment, 33(7), 2946-2962. PMID 35920739. https://pubmed.ncbi.nlm.nih.gov/35920739/

Merck & Co. (2012, April 11). PROPECIA (finasteride) tablets — US prescribing information (NDA 020788, supplements 20, 21 and 23; adds postmarketing report of sexual dysfunction continuing after discontinuation). U.S. Food and Drug Administration. https://www.accessdata.fda.gov/drugsatfda_docs/label/2012/020788s020s021s023lbl.pdf

Roehrborn, C. G., Siami, P., Barkin, J., Damiao, R., Major-Walker, K., Nandy, I., ... Montorsi, F. (2010). The effects of combination therapy with dutasteride and tamsulosin on clinical outcomes in men with symptomatic benign prostatic hyperplasia: 4-year results from the CombAT study. European Urology, 57(1), 123-131. PMID 19825505. https://pubmed.ncbi.nlm.nih.gov/19825505/

Welk, B., McArthur, E., Ordon, M., Anderson, K. K., Hayward, J., & Dixon, S. (2017). Association of suicidality and depression with 5-alpha-reductase inhibitors. JAMA Internal Medicine, 177(5), 683-691. PMID 28319231. https://pubmed.ncbi.nlm.nih.gov/28319231/

Zhou, Z., Song, S., Gao, Z., Wu, J., Ma, J., & Cui, Y. (2019). The efficacy and safety of dutasteride compared with finasteride in treating men with androgenetic alopecia: A systematic review and meta-analysis. Clinical Interventions in Aging, 14, 399-406. PMID 30863034. https://pubmed.ncbi.nlm.nih.gov/30863034/