Quick Answer: What Are the Main Side Effects of Finasteride?
Finasteride 5 mg is a 5-alpha-reductase inhibitor used for BPH in men with an enlarged prostate. Most men tolerate it, but the most important adverse effects involve sexual function, ejaculation, breast changes, mood, fertility/semen quality and PSA interpretation.
In a 4-year BPH trial, first-year adverse effects were more common with finasteride than placebo, including erectile dysfunction (8.1% vs 3.7%), reduced libido (6.4% vs 3.4%) and reduced ejaculate volume (3.7% vs 0.8%). New reports of sexual adverse effects became less frequent during later years of treatment.
Finasteride does not work by lowering testosterone. It blocks conversion of testosterone to dihydrotestosterone (DHT), reducing serum DHT by about 70%; circulating testosterone typically rises by about 10–20% but remains within the normal physiologic range.
Depression, suicidal thoughts and sexual dysfunction that persists after stopping have been reported. In 2025, the European Medicines Agency confirmed suicidal ideation as an adverse effect of oral finasteride 1 mg and 5 mg tablets, with frequency unknown.
What Is Finasteride Used For?
Finasteride is a medicine that inhibits the type II 5-alpha-reductase enzyme.
For prostate treatment, finasteride 5 mg once daily is used in appropriately selected men with symptomatic benign prostatic hyperplasia (BPH) and an enlarged prostate.
It can:
- shrink prostate volume over time;
- improve urinary symptoms;
- reduce the long-term risk of acute urinary retention; and
- reduce the likelihood of needing BPH surgery.
Finasteride 1 mg is also used for male-pattern hair loss, but this article focuses primarily on the 5 mg BPH dose.
How Does Finasteride Work?
The prostate depends partly on the androgen dihydrotestosterone (DHT).
The enzyme 5-alpha-reductase converts testosterone into DHT. Finasteride inhibits the type II form of this enzyme.
With continuous finasteride 5 mg treatment:
- serum DHT falls by approximately 70%;
- prostate DHT falls substantially;
- prostate volume typically decreases by approximately 18–28% over longer-term treatment; and
- PSA generally decreases by approximately 50% after 6–12 months.
Does Finasteride Lower Testosterone?
No.
This is one of the main errors in the old version of this page.
According to current U.S. prescribing information, circulating testosterone typically increases by about 10–20% during finasteride therapy and remains within the physiologic range.
Therefore, sexual adverse effects should not be explained by saying that finasteride causes generalized testosterone deficiency.
How Common Are Sexual Side Effects?
Sexual adverse effects are the most recognized finasteride side effects.
In the long-term finasteride 5 mg BPH study used in current U.S. prescribing information, the following drug-related events were reported:
| Adverse effect | Finasteride 5 mg — Year 1 | Placebo — Year 1 | Finasteride — Years 2–4 combined | Placebo — Years 2–4 combined |
|---|---|---|---|---|
| Erectile dysfunction / impotence | 8.1% | 3.7% | 5.1% | 5.1% |
| Reduced libido | 6.4% | 3.4% | 2.6% | 2.6% |
| Reduced ejaculate volume | 3.7% | 0.8% | 1.5% | 0.5% |
| Ejaculation disorder | 0.8% | 0.1% | 0.2% | 0.1% |
| Breast enlargement | 0.5% | 0.1% | 1.8% | 1.1% |
| Breast tenderness | 0.4% | 0.1% | 0.7% | 0.3% |
These percentages come from a specific clinical trial population and should not be interpreted as an exact prediction for an individual patient.
The trial also found that new reports of sexual adverse experiences generally became less frequent with continued treatment.
Erectile Dysfunction
Finasteride can increase the likelihood of difficulty achieving or maintaining an erection, particularly during the first year of treatment.
However, ED is also very common in the age group that develops BPH and may be caused by:
- vascular disease;
- diabetes;
- high blood pressure;
- smoking;
- obesity;
- neurological disease;
- other medications; and
- psychological factors.
Therefore, new ED while taking finasteride deserves evaluation rather than automatically assuming the medicine is the only cause.
Reducing the dose on your own is not a good strategy for BPH. The approved BPH dose is 5 mg daily. Discuss troublesome adverse effects with the prescribing clinician.
Reduced Libido
Reduced sexual desire is another recognized adverse effect.
If the change is substantial or affects quality of life, speak with your clinician. Other causes of low libido—such as depression, relationship factors, medications, low testosterone, chronic illness and sleep problems—may also need consideration.
Reduced Ejaculate Volume and Ejaculation Problems
Finasteride can reduce semen/ejaculate volume and may cause other ejaculation changes.
In healthy volunteers treated for 24 weeks, current U.S. labeling reports a median reduction in ejaculate volume of approximately 0.6 mL (22.1%), with a corresponding reduction in total sperm per ejaculate.
Sperm concentration, motility, morphology and semen pH did not show clinically meaningful changes in that study, and the semen changes were reversible after treatment was stopped.
Can Finasteride Affect Fertility?
For most men, finasteride does not appear to cause major clinically meaningful changes in standard sperm parameters.
However, rare postmarketing reports have described:
- male infertility; and
- poor semen quality.
Improvement or normalization has been reported after discontinuation.
If a couple is having difficulty conceiving—particularly if the man already has impaired semen quality—it is reasonable to discuss finasteride with the prescribing clinician or fertility specialist.
Can Sexual Side Effects Continue After Stopping Finasteride?
Persistent sexual symptoms have been reported.
Current U.S. prescribing information includes postmarketing reports of:
- erectile dysfunction continuing after discontinuation;
- reduced libido continuing after discontinuation; and
- ejaculation disorders continuing after discontinuation.
Because postmarketing reports are voluntary and often involve men with other illnesses or medications, their frequency cannot be reliably calculated and the independent contribution of finasteride can be difficult to determine.
Nevertheless, regulators including the UK MHRA specifically warn patients that sexual dysfunction may persist after treatment is stopped.
Depression and Mood Changes
Depression has been reported with finasteride.
The old article incorrectly suggested that depression is simply caused by weight gain and erectile dysfunction.
The relationship is more complex, and psychiatric symptoms should be considered a potential medication safety issue rather than dismissed as a secondary emotional response.
Finasteride and Suicidal Thoughts: Important 2025–2026 Safety Update
In June 2025, following an EU-wide safety review, the European Medicines Agency confirmed suicidal ideation (suicidal thoughts) as an adverse effect of oral finasteride tablets in both the 1 mg and 5 mg strengths.
The frequency is listed as unknown, because available data cannot provide a reliable incidence estimate.
Most reported cases in the EMA review involved the 1 mg hair-loss dose, but the warning applies to oral finasteride tablets generally.
If you feel you may act on suicidal thoughts or are in immediate danger, seek emergency medical help immediately.
Breast Enlargement and Breast Tenderness
Finasteride can cause:
- breast enlargement (gynecomastia); and
- breast or nipple tenderness.
These adverse effects are uncommon but recognized.
What About a Breast Lump or Nipple Discharge?
Any new male breast lump, persistent focal pain, nipple retraction or nipple discharge should be medically evaluated.
Male breast cancer has been reported rarely in men taking finasteride, although current prescribing information states that the relationship between long-term finasteride use and male breast cancer remains uncertain.
Do not assume a breast lump is “just a finasteride side effect.”
Testicular Pain and Blood in Semen
Postmarketing reports include:
- testicular pain; and
- hematospermia (blood in semen).
These reports do not establish how often finasteride is directly responsible.
Persistent testicular pain or repeated blood in semen should be assessed because infection, stones, prostate inflammation and other conditions can also cause these symptoms.
Allergic Reactions
Reported hypersensitivity reactions include:
- rash;
- itching;
- hives; and
- angioedema involving the lips, tongue, throat or face.
Does Finasteride Cause Weight Gain?
Weight gain is not listed as a common established adverse effect in current finasteride 5 mg prescribing information.
The old article’s explanation—that testosterone falls, metabolism is disturbed and men therefore gain weight—is not supported.
If significant weight change occurs, other possible causes should be considered, including diet, activity, fluid retention, thyroid disease, diabetes, sleep problems and other medications.
Does Finasteride Change Cholesterol or Triglycerides?
Current U.S. clinical pharmacology information reports no clinically meaningful effect on the plasma lipid profile, including total cholesterol, LDL, HDL and triglycerides.
This is consistent with the general conclusion of the previous article, although its explanation has now been updated.
Finasteride and PSA: One of the Most Important Safety Issues
Finasteride lowers PSA substantially.
After approximately 6 months, serum PSA is commonly about 50% lower.
This does not mean prostate-cancer risk has disappeared.
Current prescribing information recommends:
- establishing a new PSA baseline at least 6 months after starting finasteride;
- monitoring PSA periodically when appropriate; and
- evaluating any confirmed rise from the lowest PSA reached while taking finasteride.
For a single PSA value after at least 6 months of treatment, the measured PSA is often approximately doubled when comparing it with reference values in untreated men.
See our PSA test guide.
Does Finasteride Prevent Prostate Cancer?
No. Finasteride is not approved for prostate-cancer prevention.
The historical Prostate Cancer Prevention Trial found fewer overall prostate-cancer diagnoses among men receiving finasteride but a greater proportion of high-grade cancers in the finasteride group.
Current U.S. labeling therefore retains a warning about a possible increased risk of high-grade prostate cancer.
However, EAU guidance notes that a causal relationship has not been proven, and changes in prostate volume and cancer detection may partly explain the finding.
The practical message is:
- do not use finasteride to prevent prostate cancer;
- do not assume it causes cancer;
- and make sure PSA is interpreted correctly while taking the medication.
Pregnancy Warning: Handling Crushed or Broken Tablets
Finasteride can interfere with development of the external genitalia of a male fetus.
Therefore, someone who is pregnant or may become pregnant should not handle crushed or broken finasteride tablets.
Intact tablets are film-coated, which prevents contact with the active ingredient during normal handling.
If contact with crushed or broken tablets occurs, the exposed skin should be washed promptly with soap and water.
What About Finasteride in Semen?
Very small amounts of finasteride can be present in semen.
Current U.S. labeling reports that estimated exposure from semen is far below the dose known to affect circulating DHT levels.
If there are specific pregnancy concerns, discuss them with the prescribing clinician.
Who Should Be Especially Careful?
Before starting finasteride, tell your clinician about:
- current or previous depression or suicidal thoughts;
- significant existing sexual dysfunction;
- fertility concerns;
- liver disease;
- breast symptoms;
- your current PSA and previous PSA results; and
- other urinary conditions that could mimic BPH.
Should You Stop Finasteride Because of a Side Effect?
Do not automatically stop a prescribed BPH medicine for a mild symptom without discussing the situation with your clinician.
Whether to continue depends on:
- severity of the adverse effect;
- how much finasteride is helping your BPH;
- prostate size and progression risk;
- availability of alternative treatments; and
- your own priorities regarding urinary versus sexual function.
However, potentially serious allergic reactions require urgent treatment, and significant mood changes or suicidal thoughts require prompt medical attention.
Finasteride vs Its Benefits for BPH
Side effects should be considered in the context of the potential benefit.
Current EAU guidance recommends 5-alpha-reductase inhibitors primarily for men with moderate-to-severe LUTS and an increased risk of progression, such as men with a clearly enlarged prostate.
Unlike alpha blockers, finasteride can:
- reduce prostate volume;
- reduce long-term acute urinary-retention risk; and
- reduce long-term BPH-surgery risk.
Its disadvantage is that benefit develops slowly—usually over months rather than days or weeks.
See our BPH medication guide and how to shrink an enlarged prostate.
Questions to Ask Before or During Finasteride Treatment
- Is my prostate large enough that finasteride is likely to benefit me?
- How long should I expect before my urinary symptoms improve?
- What was my PSA before treatment?
- When should my new PSA baseline be established?
- What should I do if I develop ED or reduced libido?
- Could another medicine be contributing to my sexual symptoms?
- Should fertility concerns change my treatment plan?
- What mood changes should I report?
- Would combination therapy with an alpha blocker be more appropriate?
- What alternatives are available if side effects outweigh the benefits?
When I discuss finasteride with a patient, I explain both sides of the decision. It is one of the few BPH medicines that can actually shrink an enlarged prostate and reduce the long-term risk of urinary retention and surgery, but it works slowly and can cause sexual adverse effects.
I also make sure the patient understands that finasteride lowers DHT—not testosterone—and that his PSA will usually fall by about half. A rising PSA while taking finasteride therefore deserves attention rather than reassurance simply because the absolute number looks “normal.”
Mood changes are another issue I would now discuss explicitly. Following the 2025 European safety review, suicidal thoughts are recognized as a possible adverse effect of oral finasteride, although their frequency is unknown.
Treatment should be individualized. If side effects become troublesome, the right response is to review the indication, prostate size, PSA, other medicines and alternative BPH options rather than adjusting the dose or stopping long-term treatment without a plan.
Dr. Albana Greca, MD, MMedSc
Family Physician / General Practitioner
Founder & Lead Medical Author, Prostate Treatment Options
Medical References
DailyMed / U.S. prescribing information. Finasteride tablets 5 mg; revised April 2026. Indications, mechanism, sexual adverse reactions, semen effects, PSA interpretation, postmarketing adverse events and pregnancy warning.
European Association of Urology. 2026 Guidelines on Non-neurogenic Male LUTS: 5-alpha-reductase inhibitors—efficacy, DHT reduction, prostate-volume reduction, PSA effects and adverse events.
European Medicines Agency. 2025 referral on finasteride/dutasteride: suicidal ideation confirmed as an adverse effect of oral finasteride 1 mg and 5 mg tablets, frequency unknown.
UK Medicines and Healthcare products Regulatory Agency. Updated safety warnings for psychiatric side effects and sexual dysfunction, including sexual symptoms reported to persist after discontinuation.
Last evidence update: September 2026.
Medical information notice: This article is educational and does not replace individual prescribing advice. Do not change or stop prescription BPH treatment solely on the basis of online information without discussing the risks and alternatives with your clinician, except when urgent medical care is needed.