Finasteride: side effects explained honestly

If you are considering finasteride for hair loss, you quickly come across reports of side effects and start to feel uncertain. That is understandable, because the range runs from harmless to serious complaints. Here you get a fair account: what actually occurs, how often, how reversible, and when you should seek medical advice.

The short answer first: most men tolerate finasteride 1 mg well. The medically most important side effects affect sexual function and occur in a small proportion of users. In most cases they resolve after stopping. But there are rarer and more serious points that you should know before you decide. This is precisely why finasteride is prescription-only and belongs under medical supervision. Naming both clearly is part of making a good decision.

How likely are side effects?

The dose is decisive for how often side effects occur. For hereditary hair loss, finasteride is taken in a low dose of 1 mg per day. Many of the figures circulating online come from studies of the 5 mg dose, which is used for benign prostate enlargement. Applying those figures to hair-loss treatment overstates the picture. Here we refer to the 1 mg dose.

At this dose, most men tolerate the active ingredient without noticeable complaints. The relevant side effects affect a small proportion of users. That does not mean they are unimportant. It means that worry about the treatment and the actual frequency often diverge. Knowing both is part of making a good decision.

Sexual dysfunction: what is possible

Because finasteride intervenes in hormone metabolism and reduces the production of the hormone DHT, the most important side effects affect sexual function. You can read how this mechanism works in detail in the article Finasteride: how it works, benefits and side effects. Three types of dysfunction are possible:

• Reduced libido: less sexual desire.
• Erectile dysfunction: difficulty getting or keeping an erection.
• Ejaculation disorders: for example a reduced ejaculate volume.

At the 1 mg dose, these side effects occur in a few out of 100 men.¹ They are therefore not the rule, but also not a rare exception that no one need reckon with. How strongly the active ingredient acts on the hormone balance varies from person to person, and it varies just as much whether and how noticeably this shows up in your sex life.

It is important not to sit out such a sign. If it occurs, that is a reason to speak to the treating doctor, rather than weighing it up in silence or stopping the medication secretly. Whether a symptom is linked to the active ingredient or has another cause can often only be clarified in conversation.

Do the complaints resolve?

In most cases, yes. If you stop finasteride, the DHT level rises again, and the sexual dysfunction resolves in most of those affected, sometimes even while continuing to take it.¹ For many men this is the decisive reassurance: as a rule, the side effect is not a state without a way out.

There are, however, reports of symptoms that persist longer after stopping. How often this happens and exactly why has not been conclusively established scientifically. We do not conceal this, and we do not dramatise it either. The practical advice from this is clear: if something occurs, speak to your doctor early rather than waiting for months. The sooner the matter is on the table, the better it can be addressed, for example with an adjustment or a structured discontinuation.

Post-finasteride syndrome: what lies behind it

The term post-finasteride syndrome (PFS) groups together symptoms that those affected report even after stopping finasteride: persistent sexual dysfunction, sometimes also mood or concentration problems. The term comes up frequently in forums and the media and understandably unsettles many people.

Scientifically, the situation is less clear-cut than both extremes claim. That some men report persistent symptoms after stopping is documented. Whether behind this lies a distinct clinical condition with a clear physical cause, how often it occurs and who is particularly at risk cannot be said with certainty by current knowledge.² The available research is limited, and both the cause and the frequency remain unresolved.

Mental health: the 2025 Rote-Hand-Brief

In September 2025, the medicines authorities published a Rote-Hand-Brief (official safety notice) on orally administered finasteride, that is, the tablet.³ A Rote-Hand-Brief is an official safety notice to the medical profession. The reason: depressed mood, depression and, in rare cases, suicidal thoughts were recorded as side effects, especially with use against hair loss.

This sounds alarming at first, so here is the sober assessment. These are rare side effects, not the norm. In some of the cases they are linked to the sexual dysfunction, which can also weigh on mood. What is mainly new is that this risk is now explicitly named: the 1 mg finasteride packs contain a Patient Alert Card, which points out depressed mood, suicidal thoughts and sexual dysfunction.

For you the message is simple and important: if you notice a low mood, depressive symptoms or suicidal thoughts while taking it, stop the medication and seek medical advice. This is no reason to panic, but a clear signal not to push such a sign aside, but to take it seriously and get help.

The nocebo effect: when expectation plays a part

Some of the reported complaints are probably also linked to expectation. The nocebo effect is a general, dose-independent phenomenon: worry about a side effect can help trigger or intensify it. In a controlled study with a higher-dose finasteride preparation, men who had been informed in detail beforehand about possible sexual side effects reported exactly such symptoms considerably more often than men without this information, even though both groups received the same product.⁴

This is a delicate point, and it is easily misunderstood. Nocebo does not mean that the symptoms are imagined or less real. Someone who experiences erectile dysfunction really does experience it, regardless of how it arose. Nor is the effect an all-clear that plays down genuine side effects. It only explains why the frequency in surveys is sometimes higher than in blinded studies, and why factual, calm information is more sensible than fear or trivialisation. That is exactly our aim in this article.

Rarer points: breast, PSA level and pregnancy

Besides the sexual dysfunction, there are a few further points that are rarer but still belong here.

• Breast changes: Rarely, tightness or enlargement of the breast can occur. You should have any new changes, lumps or pain in the breast checked by a doctor.
• PSA level: Finasteride lowers the PSA level in the blood, a laboratory value from urological prostate screening. If such an examination is due, tell the doctor that you are taking it, so that the value is interpreted correctly.
• Pregnancy: For women who are pregnant or could become pregnant, finasteride is contraindicated, because the active ingredient can interfere with the genital development of a male fetus. They must not take it and should avoid skin contact with broken or crushed tablets. Intact, coated tablets, by contrast, are harmless to merely touch. Because of this mechanism, finasteride is prescribed primarily to men.

What you should do if side effects occur

The most important principle: do not act on your own, but discuss it with a doctor. Depending on the type of symptom, the right step differs:

• Mental warning signs: In the case of a low mood, depressive symptoms or suicidal thoughts, you stop the medication and seek medical advice. That is the clear recommendation from the Rote-Hand-Brief.
• Other side effects: Raise them with a doctor early, rather than stopping the medication secretly or gritting your teeth. Depending on the situation, an adjustment, a structured discontinuation or other options may then come into question.

This weighing of benefit against risk is precisely why finasteride is not available over the counter.

With us this happens under medical supervision. First you answer a medical questionnaire about your hair loss and your health. Our doctors review your answers, clarify possible contraindications and decide whether a treatment is medically suitable for you. A prescription is never guaranteed. And if a symptom occurs during treatment, you are not left alone, but have a medical point of contact. How this assessment works with us is shown in How the health questionnaire works.

How DHT and predisposition interact in hair loss is set out more broadly in Understanding hair loss. What applies to prescriptions in Germany is explained in how to get a finasteride prescription in Germany.