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Dutasteride blocks the conversion of testosterone into the more potent dihydrotestosterone and so slowly shrinks a benign enlarged prostate. It can take up to six months before the symptoms ease noticeably. Because dutasteride roughly halves the PSA level, this lab value has to be read differently during treatment.
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Prostate-specific antigen (PSA) is a protein produced by the prostate. A raised or rising PSA level can point to prostate cancer, but also to enlargement or inflammation. It is therefore used in screening — with advantages and disadvantages that every man should weigh up for himself.⁵
Dutasteride changes this value. According to the SmPC, the PSA level falls by around half after about six months of treatment.¹ This says nothing about a lower cancer risk; it is an effect of the shrunken tissue. If you do not know this, you will misread the result.
In the large REDUCE trial, fewer prostate cancers were diagnosed overall on dutasteride — mainly fewer of the slow-growing, low-aggressive forms. At the same time, tumours with a high grade of aggressiveness occurred somewhat more often in the dutasteride group.⁶ Whether dutasteride promotes such tumours, or whether they were simply detected earlier because of the smaller organ, has not been conclusively settled. The SmPC points out this finding.¹
Two things follow from this: dutasteride is not licensed to prevent prostate cancer. And careful monitoring over time — PSA read correctly, a digital rectal examination as agreed — remains just as important on treatment as without it. IQWiG provides independent information on the benefits and risks of PSA screening.⁵
After stopping, the PSA level rises back to its baseline over months. This too is part of interpreting it: a rise after stopping is to be expected at first and is assessed with the date of the last dose in mind.
Dutasteride is broken down in the liver by the enzyme CYP3A4. Medicines that strongly inhibit this enzyme can raise its level. According to the SmPC, if side effects increase, less frequent dosing may then be considered.¹
| Combination | Consequence | What to do |
|---|---|---|
| Strong CYP3A4 inhibitors such as ritonavir, ketoconazole, itraconazole | Higher dutasteride level, more side effects possible | Watch for side effects; adjustment by the practice |
| Verapamil, diltiazem (heart and blood pressure medicines) | Dutasteride is broken down more slowly | Watch for side effects and raise any complaints |
| Tamsulosin and other alpha blockers | No relevant interaction; a deliberate combination | A drop in blood pressure on standing up comes from the alpha blocker |
| Tadalafil or sildenafil | No direct interaction with dutasteride | Together with alpha blockers, keep an eye on blood pressure |
| Saw palmetto and other herbal prostate remedies | No known interaction; their own benefit is poorly supported by evidence | List them on your medication plan; see herbal medicines |
| Alcohol | No direct interaction; has a diuretic effect and increases the urge to urinate at night | Be restrained in the evening; see medications and alcohol |
The overlooked interaction is the symptoms themselves. Some medicines make passing urine harder when the prostate is enlarged: medicines with strong anticholinergic effects, some cold remedies with decongestant ingredients, certain antidepressants. If passing urine becomes noticeably more difficult after starting a new medicine, raise it. Check new prescriptions and over-the-counter purchases with the interaction check of the brite app.
Guidelines recommend 5-alpha reductase inhibitors mainly for men with moderate to severe symptoms and a markedly enlarged prostate, either alone or in combination with an alpha blocker.³
| Option | Principle | Onset of effect | Typical problem |
|---|---|---|---|
| Dutasteride | Inhibits both forms of 5-alpha reductase; the prostate shrinks | Months, up to six | Sexual side effects, halved PSA |
| Finasteride | Mainly inhibits type 2; the prostate shrinks | Months | Similar to dutasteride, also lowers PSA |
| Tamsulosin | Relaxes the muscles in the prostate and bladder neck | Days | Dizziness on standing up, ejaculation disorders; the prostate keeps growing |
| Combination | Fast relief plus long-term shrinkage | Days to months | Side effects of both medicines |
| Tadalafil | Relaxes smooth muscle, also improves erections | Weeks | Headache; not with nitrates |
Dutasteride or finasteride? Both lower DHT and shrink the prostate; dutasteride inhibits both forms of the enzyme and therefore lowers DHT more strongly. Whether this translates into a noticeable advantage for symptoms in everyday life has not been clearly shown — the effect on symptoms is considered similar.³ The choice often depends on experience, tolerability and product availability. If you switch from one active ingredient to the other, you do not need a break, but you should bear in mind that both affect the PSA level.
If medicines are not enough, surgical procedures may be considered. A note in the interest of honesty: herbal products such as saw palmetto are popular with many men, but according to current knowledge their benefit over placebo is poorly supported.² The treatment decision always lies with the treating practice.
Dutasteride is not licensed for women, children and adolescents and is contraindicated for them. In a male unborn baby, the active ingredient can disrupt the development of the external genitals. That is why the rules on handling leaking capsules and on using a condom when your partner is pregnant apply (section 4).¹
Dutasteride can reduce the volume of semen and the motility of sperm. Whether this relevantly impairs fertility in individual men has not been clearly established. If you are currently trying for a baby, raise this before starting.
According to the SmPC, dutasteride is contraindicated with severe liver impairment and used with caution with mild to moderate impairment. General rules are set out in the guide medications for kidney and liver disease.
If you take the fixed-dose combination with tamsulosin, or tamsulosin in addition, this is important before surgery for a cataract: alpha blockers can make the iris go slack during the procedure (floppy iris syndrome). Let the eye clinic know beforehand — the warning concerns the tamsulosin component, not dutasteride itself.
Whether dutasteride is continued or paused before a procedure on the prostate is decided by the urology practice. General tips are given in the guide medications before surgery.
No, at least not now. With dutasteride, six weeks is simply too early to judge: the prostate is only just beginning to shrink, and the SmPC talks of up to six months until a response. If your symptoms are weighing on you heavily at the moment, ask about a bridging treatment, for example with an alpha blocker. In the meantime, keep a simple diary — night-time trips to the toilet, stream strength, urgency. After about six months, you will then have an honest basis for the question of whether dutasteride is working for you.
Not necessarily. A drop to about half is the expected effect of dutasteride, not a statement about a lower cancer risk. According to the SmPC, your value is doubled for comparison with the normal values of untreated men — so in this example it is read like a value of about 4. From now on, the new, lower value is your reference point. What matters most is that any confirmed rise from it is taken seriously, even if it is formally within the normal range.
Usually not. Sexual side effects occur mainly in the first few months and become less frequent over time in many men. For some, however, they remain distressing, and there are isolated reports of complaints persisting after stopping. Raise the subject openly — the practice can sort out the causes, rethink the combination or bring alternatives such as tadalafil into play. Leaving out the medicine without checking first will bring the prostate symptoms back over the following months, without you knowing what the actual cause was.
Touching intact capsules is not a problem, but leaking or damaged ones are, because the active ingredient can be absorbed through the skin. Store the capsules so that she does not have to handle them. According to the SmPC, a condom is also recommended while your partner is pregnant, because small amounts of dutasteride pass into the seminal fluid. These rules also apply in the months after stopping, because the active ingredient stays in the body for a long time — ask the practice from when you are on the safe side.
So that every practice knows your value was measured on dutasteride — in your digital health history.
