A man of 52 had his PSA measured with us. Result 1.1 micrograms per litre, nicely low, and he was reassured.
Going through his details, it turned out he had been taking finasteride for his hair loss for four years. That changes how you should read such a number.
I went through the Dutch pages on finasteride. Almost all of them are about sexual side effects, and rightly so. But not one mentions what the drug does to your PSA.
What does finasteride do for hair loss?
Finasteride blocks the enzyme that converts testosterone into dihydrotestosterone, or DHT. Because DHT is what shrinks follicles in hereditary hair loss, less DHT largely removes that stimulus. In a randomised study in men with hereditary hair loss, hair growth improved compared with placebo (Kaufman, 1998).
The drug mainly slows further loss. Some thickening happens, a new hairline does not.
Two doses circulate in the Netherlands. The 1 mg tablet is for hair loss, the 5 mg tablet for an enlarged prostate. Same substance, different purpose.
It works only while you use it. Stop, and within about a year you lose what you held on to.
Why does finasteride lower your PSA?
PSA is made by prostate tissue, and that tissue depends on DHT to grow. Because finasteride blocks DHT production, your PSA drops with it. At the 5 mg dose a halving after roughly six months is well described (Guess, 1993). At the 1 mg dose for hair loss a clear fall is seen too.
This is not a detail for enthusiasts. It affects how reliable your prostate testing is.
Doctors therefore often correct by doubling the measured value before interpreting it. For dutasteride, a related drug, the same roughly fifty percent reduction after six months is described (Andriole, 2005).
Imagine two men with exactly the same result: a PSA of 1.1.
One takes nothing. For him, 1.1 is simply 1.1. The other has used finasteride for four years, and that same measurement comes with a corrected value of around 2.2.
Same number on paper, different conversation in the consulting room. That is exactly why your doctor needs to know you take it.
So always mention that you use finasteride when having your PSA measured, even if it is only 1 mg for your hair. What the value means by age is in PSA levels by age.
Which other blood values does finasteride change?
Fewer than men often think. Your total testosterone stays the same or rises slightly, because less of it is converted to DHT. Your DHT falls sharply, and that is precisely the intended effect. The main change to account for remains your PSA.
| Value | What finasteride does | What to do about it |
|---|---|---|
| PSA | Falls sharply, roughly a halving | Always report that you take it |
| DHT | Falls sharply | This is the intended effect |
| Total testosterone | Same or slightly higher | Usually no action needed |
| Liver values | Rarely abnormal | Only measure when indicated |
| Semen quality | Usually unchanged in young men | Raise it if you want children |
That last point has been studied. In young men on long-term finasteride, semen production did not change measurably (Overstreet, 1999). If you are actively trying to conceive, it still belongs on the table with your doctor.
If you take the 5 mg form for an enlarged prostate, also read enlarged prostate.
Is finasteride dangerous?
For most men the reported side effects are limited, but they are real and worth taking seriously. In the registration studies, sexual side effects such as reduced desire and erectile problems ran roughly half a percent to one percent higher than with placebo. That means most men do not get them, and a small group does.
Percentages say little if you are in that small group.
There is also a group of men reporting complaints that persist after stopping. This is called post-finasteride syndrome. How often it occurs and how it arises is not well established, and doctors disagree about it.
I find it fairer to say it that way than to wave it off or blow it up. Both happen plenty online.
What I suggest to men: read the side effects in the Farmacotherapeutisch Kompas before you start, and discuss them with the doctor prescribing it. If you notice something, do not quietly stop but report it.
If you are weighing finasteride against a treatment with no hormonal action, look at minoxidil experiences.
How long does finasteride take to work?
Count on three to six months before shedding noticeably drops, and about twelve months for the full picture. In a study assessing standardised photographs over several years, the difference from placebo persisted (Olsen, 2012). As with minoxidil, slightly more hair can let go in the first weeks.
So take that photo from above here too, before you start.
And schedule a moment at month six to evaluate honestly. Not in the mirror, but next to the first photo.
What you can do now
If you take finasteride and have your PSA measured, put it on the request form or mention it at the draw. Without that information a reassuring result can mislead.
If you are over fifty, or have prostate cancer in the family, discuss with your GP whether PSA testing suits you before starting finasteride. A baseline beforehand makes later results easier to interpret.
A separate testosterone panel shows where your hormones stand before you start a hormonal treatment. For the prostate side we have the prostate health check.
Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
References
- Kaufman KD, Olsen EA, Whiting D, et al. Finasteride in the treatment of men with androgenetic alopecia. J Am Acad Dermatol. 1998. PMID 9777765.
- Guess HA, Gormley GJ, Stoner E, Oesterling JE. The effect of finasteride on prostate-specific antigen in men with benign prostatic hyperplasia. Prostate. 1993. PMID 7678930.
- Andriole GL, Kirby R. Dutasteride: a novel dual inhibitor of 5alpha-reductase for benign prostatic hyperplasia. Expert Opin Pharmacother. 2005. PMID 15757426.
- Overstreet JW, Fuh VL, Gould J, et al. Chronic treatment with finasteride daily does not affect spermatogenesis or semen production in young men. J Urol. 1999. PMID 10492183.
- Olsen EA, Whiting DA, Savin R, et al. Global photographic assessment of men aged 18 to 60 years with male pattern hair loss receiving finasteride 1 mg or placebo. J Am Acad Dermatol. 2012. PMID 22325459.
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