What are the major side effects of finasteride?

October 9, 2025 •

4 min read

According to the NHS, finasteride side effects such as erectile dysfunction and decreased libido are rare but possible. For men considering this medication for hair loss or benign prostatic hyperplasia (BPH), understanding what are the major side effects of finasteride is crucial for making an informed decision.

Quick Summary

An overview of finasteride's major side effects, including sexual dysfunction, mental health issues like depression, gynecomastia, and rare but serious risks like prostate cancer.

Key Points

Sexual Dysfunction Is a Major Risk: Finasteride can cause decreased libido, erectile dysfunction, and ejaculation issues in some men due to its effect on hormones.
Mental Health Effects Are Reported: There is a documented association between finasteride and psychological side effects, including depression, anxiety, and in rare cases, suicidal ideation.
Gynecomastia Is a Rare Side Effect: Finasteride can alter hormonal balance, potentially leading to the development of male breast tissue (gynecomastia), which may not resolve after stopping the drug.
Post-Finasteride Syndrome (PFS) is Possible: Some individuals experience persistent sexual, psychological, and physical side effects that continue even after they have stopped taking the medication.
Dosage Matters for Some Risks: The higher 5mg dose used for BPH has been associated with a slightly increased risk of high-grade prostate cancer, though studies have not shown an increased risk of prostate cancer death.
Managing Side Effects is Possible: Strategies like dosage adjustments, consistent timing, and discussing alternative treatments like topical solutions can help mitigate side effects.
Initial Hair Shedding Can Occur: A temporary increase in hair shedding is a normal part of the finasteride treatment process for some users and is often a sign that the medication is working.

Finasteride's Mechanism of Action

Finasteride is a 5-alpha reductase inhibitor, a class of drugs that works by blocking the enzyme 5-alpha reductase. This enzyme is responsible for converting testosterone into dihydrotestosterone (DHT), a potent androgen hormone. By inhibiting this conversion, finasteride significantly lowers the levels of DHT in the body. This reduction in DHT is what helps to shrink an enlarged prostate (at a 5mg dose) and prevent the miniaturization of hair follicles that leads to male pattern baldness (at a 1mg dose). While effective, this hormonal alteration is the root cause of many of the drug's side effects.

Sexual and Reproductive Side Effects

Sexual dysfunction is one of the most commonly discussed categories of finasteride side effects. The frequency and severity can vary among individuals, but for some, the effects can be significant and impact their quality of life.

Decreased Libido

One of the most frequent sexual side effects is a lowered sex drive. Clinical studies have reported decreased libido in a small percentage of users, and for some, this effect may persist even after discontinuing the medication.

Erectile Dysfunction (ED)

Difficulty achieving or maintaining an erection is another potential side effect. ED has been reported in a subset of finasteride users, with some studies suggesting a link between longer exposure and increased likelihood. It is important to note that ED has many potential causes, and finasteride is only one possibility.

Ejaculatory Disorders

Finasteride can also lead to problems with ejaculation, such as a decrease in semen volume. This occurs due to the drug's effect on the prostate gland. While this reduction does not appear to affect overall sexual function for most men, some find it bothersome.

Potential for Infertility

Although rare, some men have reported infertility or poor semen quality while using finasteride. In many of these cases, sperm parameters improved after stopping the medication. Men planning to conceive should discuss this risk with their doctor.

Mental Health Side Effects

Evidence suggests a link between finasteride use and adverse psychological effects, which can sometimes be severe and persistent. This is an area of growing concern and has led regulatory bodies to issue updated warnings.

Depression and Anxiety

Reports indicate a higher rate of depressive symptoms and anxiety in some finasteride users compared to non-users. The altered neurosteroid hormone levels resulting from finasteride's action are a proposed mechanism for these mood changes.

Suicidal Ideation

More seriously, there have been rare reports of suicidal ideation and even suicide attempts among finasteride users. Regulatory agencies now advise monitoring patients for these symptoms, and immediate discontinuation may be recommended if they arise.

Cognitive Issues

Some patients, particularly those with post-finasteride syndrome, report cognitive issues such as brain fog, memory impairment, and difficulty concentrating.

Physical Side Effects and Other Risks

Gynecomastia

This refers to the enlargement of male breast tissue. Finasteride can cause a hormonal imbalance that increases the ratio of estrogen to androgens, leading to breast tissue growth. While gynecomastia from finasteride is rare, it is a known risk, especially with higher dosages.

Rare Cancers

Several studies have explored the link between finasteride and cancer. The Prostate Cancer Prevention Trial (PCPT) found that while finasteride reduced the overall incidence of prostate cancer, it was associated with an increased risk of developing high-grade prostate cancer. Male breast cancer has also been reported in rare cases.

Hair Shedding

Paradoxically, some men experience a temporary increase in hair shedding during the first few months of finasteride treatment. This is a normal part of the process, indicating that the medication is working to reset the hair growth cycle and replace weaker hairs with stronger ones. This shedding typically subsides within a few months.

Allergic Reactions

Like any medication, finasteride can cause allergic reactions in susceptible individuals. These can range from mild skin rashes and hives to severe, life-threatening anaphylaxis.

Post-Finasteride Syndrome (PFS)

Most finasteride side effects are temporary and resolve upon discontinuation of the drug. However, in a small subset of men, side effects persist long after the medication is stopped, a condition known as Post-Finasteride Syndrome (PFS). Symptoms can include persistent sexual dysfunction, cognitive issues, and psychological problems. While PFS is a recognized issue, a definitive causal link and effective treatment remain subjects of ongoing research.

Comparing Finasteride with Alternatives

When considering finasteride for hair loss, comparing its side effects to other treatments like minoxidil is often helpful. Minoxidil is a topical product with a different mechanism and side effect profile.


Feature	Finasteride	Topical Minoxidil
Mechanism of Action	Oral 5-alpha reductase inhibitor, reduces DHT systemically.	Topical vasodilator, improves blood circulation to follicles locally.
Sexual Side Effects	Potential for decreased libido, ED, ejaculation issues due to systemic effects.	Rare to no sexual side effects.
Mental Health Side Effects	Reported cases of depression, anxiety, and suicidal ideation.	Minimal systemic absorption, lower risk of mental health effects.
Physical Side Effects	Rare gynecomastia, temporary shedding, potential cancer risks.	Scalp irritation, itching, dryness; temporary shedding.
Duration of Effect	Must be used continuously to maintain effects; discontinuation reverses benefits.	Must be used continuously; stopping reverses hair growth.

Conclusion

Understanding the major side effects of finasteride is essential for anyone considering its use. While many individuals experience no side effects, or only mild and temporary ones, the potential for sexual dysfunction, mental health issues, and rare but serious risks like cancer and Post-Finasteride Syndrome should be carefully considered. Open and honest communication with a healthcare provider is paramount to weigh the risks and benefits based on individual health history. For persistent or concerning side effects, options like dosage adjustment, alternative treatments, or discontinuation should be discussed. As with any medical treatment, being informed and consistent with medical advice is key to a successful outcome. More information on finasteride is available from trusted resources such as MedlinePlus.

Frequently Asked Questions

PFS is a condition where a small number of men who have taken finasteride experience persistent sexual, mental, and physical side effects even after they have stopped taking the medication.

Yes, psychological side effects such as depression and anxiety have been reported by some finasteride users. The U.S. FDA has added warnings for these potential side effects.

While it's rare, gynecomastia caused by finasteride may not go away even after stopping the drug. In such cases, surgery is often the most effective treatment for permanent removal.

Some studies, particularly concerning the 5mg dose for BPH, have found a slightly increased risk of developing high-grade prostate cancer, but not an increased risk of death from the disease. Male breast cancer has also been reported in rare instances.

Yes, for many, the initial hair shedding phase is a normal reaction to starting treatment. It signifies that the hair growth cycle is resetting and making way for new, healthier hairs to grow.

Management strategies include consulting a doctor about dosage adjustments, maintaining a consistent daily schedule, and discussing alternative treatments like topical finasteride or minoxidil if side effects are bothersome.

Pregnant women should not handle crushed or broken finasteride tablets, as the drug can be absorbed through the skin and cause birth defects in a male fetus. If contact occurs, the area should be washed immediately with soap and water, and a doctor should be consulted.

Yes, side effects are more likely with the higher 5mg dose used for BPH. The lower 1mg dose for hair loss is typically associated with sexual side effects, though the risk is lower.