Dutasteride side effects: what it does to your libido and your PSA

The dutasteride side effects men report most are lower libido, erection problems, less ejaculate and sometimes tender or swollen breasts. Dutasteride also lowers your PSA to roughly half after about six months. That last one is not a side effect, but it does change how your result must be read.

That PSA halving is high on my list of things someone should have told you. A PSA of 1.4 on dutasteride is not the same number as a PSA of 1.4 without it.

Yet men tell me nobody explained it.

What are the side effects of dutasteride?

The most reported side effects are sexual: less desire, harder to get or keep an erection, and less volume at ejaculation. Tender or swollen breasts also occur. The Dutch Farmacotherapeutisch Kompas notes that the incidence of sexual side effects decreases over the course of treatment.

That matters more than it sounds. It means the first six months need not represent year two.

The explanation is in the mechanism. Dutasteride blocks the enzyme 5-alpha-reductase, which converts testosterone into dihydrotestosterone, or DHT. Less DHT means a smaller prostate, and it also means less DHT signal in other tissue.

What DHT does elsewhere in your body is in hair loss in men and DHT. Breast tissue has its own story: see gynecomastia and its hormonal causes.

How long before dutasteride works?

Expect three to six months before you notice a difference in your urinary symptoms. That is fundamentally unlike an alpha blocker such as tamsulosin, which works within days to two weeks. Dutasteride shrinks glandular tissue, and that takes time.

This is where men often go wrong. They stop after six weeks because nothing has happened.

The CombAT study followed men on dutasteride, tamsulosin or the combination. The two-year results appeared in the Journal of Urology in 2008 (PMID 18082216) and the four-year outcomes in BJU International in 2011 (PMID 21332630). The pattern is that the 5-ARI effect builds over years.

The fast route and the slow route side by side are in tamsulosin: how it works and what your doctor checks.

Does dutasteride halve your PSA?

Yes. Dutasteride lowers your PSA, and the value stabilises after about six months at roughly half your starting level. That is why a doctor sets a new baseline after six months of treatment. If you stop, your PSA returns to the old level within about six months.

This is the arithmetic nobody writes down, so here it is.

Two men aged 66 both get a PSA result of 2.0 micrograms per litre. The first takes no prostate medication, the second has been on dutasteride for a year. Same result, and yet for the second a doctor is looking at a value that untreated would sit around 4.0.

Two things matter here. The doubling rule of thumb only applies once you are at least six months in, and it is an approximation rather than an exact formula.

More importantly, a rise from your lowest value on treatment is the signal a doctor looks at. The Farmacotherapeutisch Kompas notes that a confirmed rise from the nadir deserves attention, and that not taking the drug as prescribed can also explain it.

To see your own value you can order a PSA test. When you discuss the result, always mention that you take a 5-ARI and since when. What the value itself means is on our page about PSA.

What is the difference between dutasteride and finasteride?

Both block 5-alpha-reductase, but dutasteride blocks type 1 as well as type 2 of that enzyme, while finasteride mainly acts on type 2. Practically that means a stronger fall in DHT with dutasteride. Both drugs lower PSA by roughly half.

So for the PSA arithmetic the choice matters little. For the degree of DHT suppression it does.

In the Netherlands finasteride is also used at a lower dose for hair loss, dutasteride is not. We wrote about that in finasteride experiences and your PSA.

There is one more difference that gets little attention. Dutasteride has been studied extensively in prostate cancer prevention, with results more nuanced than hoped. An overview appeared in Drugs Today in 2011 (PMID 21431101). That same research programme also saw a higher number of adverse cardiovascular events than placebo.

Do the sexual side effects go away if you stop?

For some men they do. The Farmacotherapeutisch Kompas reports that around half of this kind of side effect resolves within six months of stopping. Incidence also falls during continued use. For some men complaints persist longer.

I say that plainly, because "it will pass" is too easy.

What you do know: ejaculate volume often drops, because the prostate and seminal vesicles produce less fluid. That is a direct result of less DHT signal, not of something being broken.

Erection problems rarely have a single cause. Blood vessels, blood sugar, blood pressure medication and hormones all play a part. See enlarged prostate and erectile problems and ED medications compared.

What is in Combodart?

Combodart holds dutasteride 0.5 mg and tamsulosin 0.4 mg in one capsule. So you get a fast-acting alpha blocker and a slow-acting 5-ARI together. For your PSA result the dutasteride side rules: expect roughly a halving after six months.

That is why combination capsules cause so much confusion. One box, two opposite effects on your blood value.

The CombAT study is precisely the study of this combination: dutasteride plus tamsulosin against each drug alone (PMID 21332630). What the tamsulosin side does to your ejaculation comes from the 2014 Gacci meta-analysis (PMID 24708055).

What to do with this

Find out whether a PSA value exists from before you started dutasteride. That number is your real baseline, and without it every later result is harder to place.

If you are unsure of the start date, ask your pharmacy. Six months is the point after which the halving is stable, so that date matters.

The other routes for an enlarged prostate are in alternatives to tamsulosin and treatment options for an enlarged prostate.

Every Caliber blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.

References

• Roehrborn CG, et al. Clinical outcomes after combined therapy with dutasteride plus tamsulosin or either monotherapy in men with benign prostatic hyperplasia by baseline characteristics: 4-year results from the CombAT trial. BJU Int. 2011. PMID 21332630.
• The effects of dutasteride, tamsulosin and combination therapy on lower urinary tract symptoms in men with benign prostatic hyperplasia and prostatic enlargement: 2-year results from the CombAT study. J Urol. 2008. PMID 18082216.
• Rove KO, Crawford ED. Dutasteride: novel milestones in prostate cancer chemoprevention. Drugs Today. 2011. PMID 21431101.
• Gacci M, et al. Impact of medical treatments for male lower urinary tract symptoms due to benign prostatic hyperplasia on ejaculatory function: a systematic review and meta-analysis. J Sex Med. 2014. PMID 24708055.
• Farmacotherapeutisch Kompas. Drug monograph dutasteride. Accessed 2026. farmacotherapeutischkompas.nl.