Finasteride
5-Alpha Reductase Inhibitor for Hair Loss and Prostate Enlargement
Finasteride is a prescription medication that works by blocking the enzyme 5-alpha reductase, which converts testosterone into dihydrotestosterone (DHT). It is used at a low dose (1 mg) to treat male pattern hair loss (androgenetic alopecia) in men aged 18 to 41 years, and at a higher dose (5 mg) to treat benign prostatic hyperplasia (BPH) in older men. Finasteride is for men only and must never be used by women or children.
Quick Facts
Key Takeaways
- Finasteride reduces DHT levels by approximately 70%, slowing hair loss and, in many cases, promoting regrowth after 3 to 6 months of daily use.
- The 1 mg dose is approved for male pattern hair loss (men 18-41), while the 5 mg dose is used for benign prostatic hyperplasia (BPH).
- Pregnant women must never handle crushed or broken finasteride tablets, as the drug can cause birth defects in male foetuses.
- Common side effects include decreased libido, erectile dysfunction, and ejaculation disorders, which typically resolve after stopping treatment.
- Depression, mood changes, and persistent sexual side effects have been reported in some patients and should be discussed with a healthcare provider.
What Is Finasteride and What Is It Used For?
Finasteride belongs to a class of medications known as 5-alpha reductase inhibitors. It works by selectively blocking the Type II isoenzyme of 5-alpha reductase, the enzyme responsible for converting testosterone into dihydrotestosterone (DHT). DHT is an androgen hormone that plays a central role in the miniaturisation of hair follicles in men who are genetically predisposed to androgenetic alopecia (male pattern baldness). By reducing DHT levels in the scalp by approximately 60%, finasteride slows down and often reverses the hair thinning process.
Male pattern hair loss is an extremely common condition that affects a significant proportion of men as they age. It is characterised by a progressive thinning of hair at the temples and crown, driven by a combination of genetic susceptibility and the effects of DHT. In affected individuals, DHT shortens the growth phase (anagen) of the hair cycle and causes the hair follicles to shrink over time, leading to thinner, shorter hairs and eventually bare scalp. Finasteride at a dose of 1 mg daily is approved for the treatment of early-stage male pattern hair loss in men between 18 and 41 years of age.
Clinical trials lasting up to five years have demonstrated that finasteride 1 mg effectively slows hair loss in the majority of men. In the landmark studies by Kaufman and colleagues (2002), approximately 90% of men treated with finasteride experienced either hair regrowth or no further hair loss, compared with continued progression in the placebo group. At least half of the men who took finasteride for five years showed measurable improvement in hair density. It is important to note that finasteride is only effective for men with mild to moderate hair loss and is not expected to benefit those who are completely bald or who have lost hair in large patches.
At the higher dose of 5 mg, finasteride is used to treat benign prostatic hyperplasia (BPH), a non-cancerous enlargement of the prostate gland that commonly affects men over the age of 50. BPH can cause bothersome urinary symptoms such as difficulty starting urination, weak urine stream, frequent need to urinate (especially at night), and a sensation of incomplete bladder emptying. By reducing the size of the prostate gland through DHT lowering, finasteride 5 mg helps to relieve these symptoms and reduce the risk of acute urinary retention and the need for prostate surgery.
Finasteride is available under multiple brand names and as generic formulations worldwide. Well-known brand names include Propecia (1 mg for hair loss) and Proscar (5 mg for BPH). Generic versions are manufactured by numerous pharmaceutical companies, including Finasterid STADA, Finasteride Teva, Finasterid Sandoz, Finasteride Accord, Finasterid Actavis, Finasterid Amarox, Finasteride Medical Valley, and Finasterid Aurobindo, among others. All approved formulations contain the same active ingredient and are considered therapeutically equivalent.
What Should You Know Before Taking Finasteride?
Contraindications
Do not take finasteride if you are allergic (hypersensitive) to finasteride or to any of the other ingredients in the tablet. The inactive ingredients typically include lactose monohydrate, microcrystalline cellulose, pregelatinised maize starch, sodium starch glycolate (type A), magnesium stearate, and a film-coating containing hypromellose, titanium dioxide (E171), iron oxides (E172), and macrogol 6000. If you have a known intolerance to lactose, you should inform your doctor before starting treatment.
Finasteride must not be used by women. Clinical studies have demonstrated that finasteride is ineffective for the treatment of female pattern hair loss (female androgenetic alopecia). More importantly, finasteride poses a serious risk to pregnant women. If a woman who is carrying a male foetus comes into contact with finasteride — even by handling crushed or broken tablets — the drug may be absorbed through the skin and can potentially cause abnormal development of the baby's genital organs. Intact film-coated tablets are safe to handle because the coating prevents contact with the active ingredient, but tablets must never be crushed, broken, or split.
Finasteride should not be taken by men who are already using another medication containing finasteride or any other 5-alpha reductase inhibitor, such as dutasteride, for the treatment of BPH or any other condition. Combining these drugs provides no additional benefit and may increase the risk of side effects.
Warnings and Precautions
Mood changes including depression and, less commonly, suicidal thoughts have been reported in men taking finasteride. If you experience persistent low mood, feelings of hopelessness, or thoughts of self-harm, stop taking finasteride immediately and contact your doctor as soon as possible.
Finasteride must not be used by children or adolescents under 18 years of age. There are no clinical data to support use in this age group, and the hormonal effects of the drug could interfere with normal development during puberty.
Contact your doctor promptly if you notice any changes in your breast tissue, such as lumps, pain, breast enlargement (gynaecomastia), or changes to the nipple. Although rare, male breast cancer has been reported in men taking finasteride, and any breast changes should be evaluated by a healthcare professional to rule out a serious underlying condition.
Finasteride can affect the results of a blood test called prostate-specific antigen (PSA), which is used to screen for prostate cancer. Finasteride typically lowers PSA values by approximately 50% after six months of treatment. If you are having PSA testing, it is essential that you inform your doctor that you are taking finasteride so that the results can be interpreted correctly. Your doctor will need to double the measured PSA value to estimate what the true PSA level would be. PSA testing should be performed before initiating finasteride therapy and at regular intervals during treatment.
There is evidence that finasteride may reduce male fertility. The drug can lower sperm count, reduce semen volume, and decrease sperm motility in some men. Men who are planning to father a child should discuss with their doctor whether to discontinue finasteride before attempting conception. Normalisation or improvement of sperm quality has been reported after stopping treatment, though no long-term studies on the effects of finasteride on male fertility have been completed.
Sexual dysfunction, including decreased libido, erectile difficulties, and ejaculation disorders, has been reported during finasteride therapy. In most cases, these effects resolve after discontinuation. However, some men have reported persistent sexual side effects that continued after stopping the drug. This phenomenon, sometimes referred to as post-finasteride syndrome, has been the subject of ongoing investigation by regulatory authorities and the medical community. If you experience symptoms of sexual dysfunction, speak with your doctor, who may consider stopping treatment.
Pregnancy and Breastfeeding
Finasteride must not be used by women. Women who are pregnant or who may become pregnant must not handle crushed or broken finasteride tablets. If finasteride is absorbed through the skin or swallowed by a woman who is pregnant with a male foetus, the baby could be born with malformed genital organs.
The film coating on finasteride tablets prevents contact with the active substance during normal handling, provided the tablets are not crushed, broken, or split. However, as an additional precaution, if your sexual partner is or may become pregnant, you should either avoid exposing her to your semen (for example, by using a condom) or discontinue finasteride treatment. This is because finasteride is present in very small amounts in seminal fluid.
Driving and Operating Machinery
There are no data suggesting that finasteride impairs the ability to drive vehicles or operate machinery. Based on the pharmacological profile of the drug and the clinical evidence available, finasteride is not expected to affect your ability to drive or use machines safely.
How Does Finasteride Interact with Other Drugs?
One of the pharmacological advantages of finasteride is its relatively low potential for drug-drug interactions. Clinical studies have not identified significant interactions between finasteride 1 mg and other commonly prescribed medications. The drug is metabolised primarily by the cytochrome P450 3A4 enzyme system in the liver, but it does not appear to significantly inhibit or induce any major CYP enzymes at therapeutic doses, reducing the likelihood of interactions with other substrates of these enzyme systems.
Despite this favourable interaction profile, there are some important considerations. There is no information available regarding the concomitant use of finasteride 1 mg and topical minoxidil (a medication commonly applied to the scalp to treat hair loss). While many men do use both treatments simultaneously in clinical practice, the combination has not been formally studied in clinical trials, and your doctor should be consulted before using both drugs together.
The following table summarises the known and potential drug interactions with finasteride. Always inform your doctor or pharmacist about all medications you are taking, including over-the-counter drugs, herbal supplements, and vitamins.
| Interacting Drug | Severity | Effect | Recommendation |
|---|---|---|---|
| Dutasteride (and other 5-alpha reductase inhibitors) | Major | Duplicate mechanism of action; no added benefit, increased risk of side effects | Do not combine; choose one agent only |
| Topical Minoxidil | Unknown | No formal interaction studies conducted; often used together in practice | Consult your doctor before combining |
| CYP3A4 Inhibitors (e.g. ketoconazole, itraconazole) | Minor | May slightly increase finasteride plasma levels; not considered clinically significant at standard doses | No dose adjustment generally required |
| St John's Wort (Hypericum perforatum) | Minor | CYP3A4 inducer; may potentially reduce finasteride efficacy | Discuss with your doctor if taking regularly |
| Testosterone supplementation | Moderate | Exogenous testosterone may partially counteract finasteride's effect on DHT reduction | Inform your doctor; monitoring may be needed |
Finasteride lowers PSA levels by approximately 50%. If you are having PSA blood tests for prostate screening, always inform your doctor that you are taking finasteride so that results can be properly interpreted. Your doctor will typically double the measured value.
What Is the Correct Dosage of Finasteride?
Always take finasteride exactly as prescribed by your doctor. If you are unsure about the correct dose, consult your doctor or pharmacist. Do not change the dose or stop taking the medication without first speaking to your doctor. It is important to understand that finasteride does not work faster or better if taken more than once per day; consistent daily dosing is the key to achieving optimal results.
Adults — Male Pattern Hair Loss
Finasteride 1 mg for Androgenetic Alopecia
Dose: One 1 mg tablet taken once daily.
Administration: Swallow the tablet whole with water. Do not crush, break, or split the tablet. May be taken with or without food.
Duration: Daily use for at least 3 to 6 months is required before results may become noticeable. Treatment should be continued for at least 12 months to fully assess efficacy. If no improvement is seen after 12 months, discuss with your doctor whether to continue treatment.
Approved age range: 18 to 41 years.
Adults — Benign Prostatic Hyperplasia (BPH)
Finasteride 5 mg for BPH
Dose: One 5 mg tablet taken once daily.
Administration: Swallow whole with water. Do not crush or break. May be taken with or without food.
Duration: Treatment may need to be continued for at least 6 months to assess whether a beneficial response has been achieved. Long-term therapy is typically required.
Children and Adolescents
Finasteride is not approved for use in children or adolescents under 18 years of age. There are no paediatric dosing recommendations, as safety and efficacy have not been established in this population. The hormonal effects of DHT suppression may interfere with normal pubertal development, and finasteride should never be given to minors.
Elderly Patients
No dose adjustment is required for elderly patients when using finasteride 5 mg for BPH. The pharmacokinetics of finasteride are not significantly altered in older adults, though the elimination rate may be slightly slower. Finasteride 1 mg for hair loss has not been specifically studied in men over 41 years of age, and its use for this indication in older men is generally not recommended.
Missed Dose
If you forget to take a dose of finasteride, do not take a double dose to make up for the missed one. Simply skip the missed dose and continue with your regular dosing schedule. Taking an extra tablet will not accelerate results and may increase the risk of side effects.
Overdose
If you take more finasteride than prescribed, or if someone (such as a child) accidentally ingests the medication, contact your doctor, hospital, or poison control centre immediately for assessment and advice. In clinical studies, single doses of up to 400 mg and multiple doses of up to 80 mg per day for three months did not result in dose-related adverse effects. There is no specific antidote for finasteride overdose; treatment is supportive and symptomatic.
Stopping Treatment
If you stop taking finasteride for hair loss, the hair you gained or maintained during treatment will likely be lost within 9 to 12 months. The hair loss process resumes once finasteride is discontinued because DHT levels return to their pre-treatment levels within approximately two weeks. For this reason, continuous daily use is recommended for as long as you wish to maintain the benefits. You and your doctor should periodically review whether continued treatment is appropriate.
| Indication | Strength | Dose | Frequency | Duration |
|---|---|---|---|---|
| Male Pattern Hair Loss | 1 mg | 1 tablet | Once daily | 3-6 months minimum; ongoing |
| Benign Prostatic Hyperplasia (BPH) | 5 mg | 1 tablet | Once daily | 6+ months; long-term |
What Are the Side Effects of Finasteride?
Like all medicines, finasteride can cause side effects, although not everyone experiences them. The side effects of finasteride tend to be mild and transient in most men. Many side effects resolve on their own during continued treatment or disappear after the medication is discontinued. However, it is important to be aware of both common and rare adverse effects so that you can recognise them and seek appropriate medical advice if needed.
Stop taking finasteride and call your doctor immediately if you experience signs of angioedema: swelling of the face, lips, tongue, or throat; difficulty swallowing; hives; or difficulty breathing. Also stop taking finasteride and seek urgent medical help if you experience suicidal thoughts.
Uncommon Side Effects
May affect up to 1 in 100 men
- Decreased sex drive (libido)
- Depression
- Difficulty getting or maintaining an erection (erectile dysfunction)
- Ejaculation problems, including reduced volume of ejaculate
Not Known (Frequency Cannot Be Estimated)
Reported from post-marketing surveillance
- Allergic reactions including skin rash, itching, and hives (urticaria)
- Angioedema (swelling of face, lips, tongue, or throat)
- Swollen or tender breasts (gynaecomastia)
- Testicular pain
- Palpitations (awareness of heartbeat)
- Persistent erectile dysfunction after stopping treatment
- Persistent decreased libido after stopping treatment
- Persistent ejaculation disorders after stopping treatment
- Infertility (reported in men on long-term treatment who also had other risk factors for reduced fertility)
- Elevated liver enzymes
- Anxiety
- Suicidal thoughts
Persistent Side Effects
While most side effects of finasteride are reversible and resolve after discontinuation, there have been post-marketing reports of sexual, emotional, and cognitive side effects that persisted in some patients even after stopping the medication. These persistent effects include continued erectile dysfunction, reduced libido, ejaculation difficulties, depression, and anxiety. The exact incidence of these persistent effects is difficult to determine from spontaneous reporting, and they remain the subject of ongoing scientific investigation.
Regulatory agencies, including the European Medicines Agency (EMA) and the U.S. Food and Drug Administration (FDA), have acknowledged these reports and have required updated labelling to include warnings about the potential for persistent side effects. If you notice any lasting changes in sexual function or mood after stopping finasteride, report these to your doctor.
Breast Changes
Although rare, changes in breast tissue have been reported in men taking finasteride. These include breast tenderness, breast enlargement (gynaecomastia), and nipple changes. If you notice any lumps, pain, or other changes in your breast tissue, contact your doctor promptly, as these changes should be evaluated to rule out serious conditions, including male breast cancer, which has been reported in very rare cases.
Effects on Fertility
Infertility has been reported in men who took finasteride for extended periods and who also had other risk factors that could affect fertility. Studies have shown that finasteride can reduce sperm count and semen volume, and may decrease sperm motility. Normalisation or improvement of sperm quality has been observed after discontinuing finasteride. If you are planning to conceive, discuss with your doctor whether to temporarily stop treatment. No long-term controlled studies on the impact of finasteride on male fertility have been completed.
If you experience any side effects, including those not listed here, report them to your doctor or pharmacist. Reporting suspected adverse reactions helps regulatory agencies monitor the benefit-risk balance of medicines. You can also report side effects directly to your national medicines agency (e.g. the MHRA in the UK, the FDA in the US, or the EMA in the EU).
How Should You Store Finasteride?
Keep finasteride out of the sight and reach of children at all times. Store the medication in its original packaging to protect from moisture and light. No special storage temperature conditions are required; room temperature storage is appropriate for most formulations. Avoid storing finasteride in the bathroom or near a sink, where humidity levels may be high.
If your finasteride tablets come in a plastic bottle with a screw cap, use the tablets within 4 months of first opening the bottle. Check the expiry date printed on the outer carton (after "EXP") before taking any tablet. The expiry date refers to the last day of the stated month. Do not use finasteride after the expiry date.
Do not dispose of unused finasteride tablets by flushing them down the toilet or throwing them in household waste. Instead, return any unused medication to your pharmacy for safe disposal. Proper disposal of medicines helps protect the environment, as pharmaceutical residues can potentially contaminate water supplies and ecosystems.
What Does Finasteride Contain?
The active substance in each tablet is finasteride, available in strengths of 1 mg and 5 mg. The active ingredient is the component responsible for the drug's therapeutic effect — lowering DHT levels by inhibiting the Type II 5-alpha reductase enzyme.
The other ingredients (excipients) in a typical finasteride tablet include:
- Tablet core: Lactose monohydrate, microcrystalline cellulose, pregelatinised maize starch, lauroyl macrogol glycerides, sodium starch glycolate (type A), and magnesium stearate.
- Film-coating: Hypromellose, titanium dioxide (E171), red and yellow iron oxides (E172), and macrogol 6000.
Finasteride 1 mg tablets are typically reddish-brown, round, biconvex, film-coated tablets. Depending on the manufacturer, they may be marked with an identifying imprint (for example, "F1" on one side). Finasteride 5 mg tablets are generally blue, round, or apple-shaped film-coated tablets. The film coating serves two purposes: it protects the active ingredient from moisture and light, and it prevents skin contact with finasteride — which is particularly important for the safety of women who may handle the tablets.
Finasteride tablets contain lactose monohydrate. If you have been told by your doctor that you have an intolerance to some sugars, consult your doctor before taking this medicine. Finasteride contains less than 1 mmol sodium (23 mg) per tablet, which means it is essentially sodium-free.
Frequently Asked Questions About Finasteride
Medical References
All medical information on this page is based on peer-reviewed research, international clinical guidelines, and approved product labelling from regulatory agencies. The following sources were consulted:
- Kaufman KD, Olsen EA, Whiting D, et al. Finasteride in the treatment of men with androgenetic alopecia. J Am Acad Dermatol. 1998;39(4 Pt 1):578-589. doi:10.1016/S0190-9622(98)70007-6
- Kaufman KD. Long-term (5-year) multinational experience with finasteride 1 mg in the treatment of men with androgenetic alopecia. Eur J Dermatol. 2002;12(1):38-49.
- European Medicines Agency (EMA). Finasteride Summary of Product Characteristics. Updated 2023. Available at: www.ema.europa.eu
- U.S. Food and Drug Administration (FDA). Propecia (finasteride) Prescribing Information. Revised 2024. Available at: www.accessdata.fda.gov
- British National Formulary (BNF). Finasteride. National Institute for Health and Care Excellence (NICE). Updated 2025. Available at: bnf.nice.org.uk
- Thompson IM, Goodman PJ, Tangen CM, et al. The influence of finasteride on the development of prostate cancer. N Engl J Med. 2003;349(3):215-224. doi:10.1056/NEJMoa030660
- World Health Organization (WHO). WHO Model List of Essential Medicines. 23rd List, 2023. Available at: www.who.int
- Irwig MS. Persistent sexual side effects of finasteride: Could they be permanent? J Sex Med. 2012;9(11):2927-2932. doi:10.1111/j.1743-6109.2012.02846.x
- Traish AM. Post-finasteride syndrome: a surmountable challenge for clinicians. Fertil Steril. 2020;113(1):21-50. doi:10.1016/j.fertnstert.2019.11.030
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