Dutasteride (Avodart)

Patient information

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What are the possible side effects of AVODART? AVODART may cause serious side effects, including:

Rare and serious allergic reactions, including:

• Swelling of your face, tongue, or throat
• Serious skin reactions, such as skin peeling

Get medical help right away if you have these serious allergic reactions.

Higher chance of a more serious form of prostate cancer

The most common side effects of AVODART include:

trouble getting or keeping an erection (impotence)*
a decrease in sex drive (libido)*
ejaculation problems*

• enlarged or painful breasts. If you notice breast lumps or nipple discharge, you should talk to yourhealthcare provider.

*Some of these events may continue after you stop taking AVODART.

Depressed mood has been reported in patients receiving AVODART.

Highlights of Prescribing Information

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5.6 Effect on Semen Characteristics

The effects of dutasteride 0.5 mg/day on semen characteristics were evaluated in healthy men throughout 52 weeks of treatment and 24 weeks of post-treatment follow-up. At 52 weeks, compared with placebo, dutasteride treatment resulted in mean reduction in total sperm count, semen volume, and sperm motility; the effects on total sperm count were not reversible after 24 weeks of follow-up. Sperm concentration and sperm morphology were unaffected and mean values for all semen parameters remained within the normal range at all timepoints. The clinical significance of the effect of dutasteride on semen characteristics for an individual patient’s fertility is not known [see Use in Specific Populations (8.3)].


6.1 Clinical Trials Experience


• The most common adverse reactions reported in subjects receiving AVODART were impotence, decreased libido, breast disorders (including breast enlargement and tenderness), and ejaculation disorders.

• Trial withdrawal due to adverse reactions occurred in 4% of subjects receiving AVODART and 3% of subjects receiving placebo in placebo-controlled trials with AVODART. The most common adverse reaction leading to trial withdrawal was impotence (1%).

a These sexual adverse reactions are associated with dutasteride treatment (including monotherapy and combination with tamsulosin). These adverse reactions may persist after treatment discontinuation. The role of dutasteride in this persistence is unknown.
b Includes breast tenderness and breast enlargement.

6.2 Postmarketing Experience

The following adverse reactions have been identified during post-approval use of AVODART. […] These reactions have been chosen for inclusion due to a combination of their seriousness, frequency of reporting, or potential causal connection to AVODART.

Immune System Disorders

Hypersensitivity reactions, including rash, pruritus, urticaria, localized edema, serious skin reactions, and angioedema.


Male breast cancer.

Psychiatric Disorders

Depressed mood.

Reproductive System and Breast Disorders

Testicular pain and testicular swelling.

Comparing finasteride and dutasteride

Finasteride and dutasteride both inhibit the 5-alpha reductase enzyme, but there are a number of differences in their pharmacology, history and current use.

Brand namePropecia (finasteride 1 mg) for AGA
Proscar (finasteride 5 mg) for BPH
Avodart (dutasteride 0.5 mg)
Drug developerMerck & Co.GlaxoSmithKline
Current drug marketerOrganon [1]GSK [2]
Regulatory statusProscar approved in U.S. in 1992
Propecia approved in U.S. in 1997
Prescribed off-label for prevention of prostate cancer
Avodart for BPH approved in U.S. in 2001
Approved for treatment of AGA in South Korea & Japan. Not approved for AGA in U.S. or Europe.
Pharmacology & pharmacokineticsInhibits 5-AR types 2 and 3 [3]; weak inhibitor of 5-AR type 1
Half life: 5-6 hours
Inhibits 5-AR types 1, 2 and 3 [3]
Half-life: approx. 5 weeks
AGA, androgenetic alopecia / male pattern hair loss; BPH, benign prostatic hyperplasia / enlarged prostate.
Notes: 1. Propecia and Proscar were transferred to Organon in a 2021 spinoff from Merck.
2. GlaxoSmithKline was renamed to GSK in 2022. 3. After both drugs were approved, 5-AR type 3 was identified, and it was reported to be “potently inhibited” by finasteride and dutasteride (Yamana et al., 2010)

Some natural substances such as saw palmetto, black pepper and ginseng also have 5-alpha reductase inhibiting properties (see this bibliography).

See also: Firsthand experiences – Vol. XI: Dutasteride