Finasteride

What is finasteride?

Finasteride is classified as a 5-alpha-reductase enzyme inhibitor primarily used to treat a condition called benign prostatic hyperplasia (BPH) or enlarged prostate in men. When the prostate becomes enlarged, it blocks the flow of urine and eventually causes difficulty urinating. Finasteride reduces the size of the prostate gland over time. The drug works by inhibiting the enzyme that converts testosterone to dihydrotestosterone (DHT), the hormone responsible for prostate growth. This causes the enlarged prostate gland to shrink, improving urinary issues in most men with BPH.¹ ²

What You Need To Know About Prostate Cancer

Finasteride is also prescribed to treat male-pattern hair loss, also known as androgenic alopecia (AGA). It works because the enzyme it blocks is also present in the hair follicles of the scalp. Research has demonstrated the prevention of further hair loss with the long-term use of finasteride taken orally or applied in gel form.³ ⁴

Finasteride is a generic drug that is also available as the brands Proscar (for treating BPH) and Propecia (for hair loss).

What is finasteride used to treat?

Finasteride has been approved by the US Food and Drug Administration (FDA) as an oral medication for the treatment of BPH and AGA. The medication is indicated for use exclusively in men.⁵ ⁶

The drug improves the symptoms of BPH and reduces the likelihood of surgical intervention. Without this treatment, a patient with an enlarged prostate may need a tube inserted into the bladder to urinate, a surgical procedure to reduce the prostate gland tissue from inside the urethra, or the surgical removal of the prostate gland.

Finasteride is also indicated for treating AGA, the most common form of hair loss in men. The drug is effective in slowing down hair loss, but it doesn’t stop it completely. Once the drug is discontinued, hair loss will resume.

Off-label uses of finasteride include treating female pattern hair loss and excessive hair growth in women, but these are not US FDA-approved uses for the drug. The US FDA has not determined the safety of finasteride for female patients and the pediatric population.⁷

Dosage forms and strengths

Finasteride is available by prescription only in the following strengths:⁸

• 1mg tablets (generic, Propecia)

• 5mg tablets (generic, Proscar)

How do you take finasteride?

Swallow each tablet whole without breaking, chewing, crushing, or dividing it. You can take your medication with or without food, but you should try to take it around the same time each day.⁹

Seeing results

Finasteride is rapidly absorbed in the intestines and metabolized in the liver. The drug’s metabolites are then expelled through the intestinal and urinary tracts. People taking the medication for BPH will need to continue for at least six months before seeing results. The most commonly noticed improvements are in urinary emptying and flow. Keep in mind that the prostate may shrink without improving urinary symptoms. Should this occur, your physician may recommend more time with the treatment or another intervention.¹⁰ ¹¹ ¹² ¹³ ¹⁴

The first sign of positive results from finasteride for treating AGA may take several months due to the slow hair growth process. General improvements should be visible within 12 months of initiating treatment.¹⁵

Who should not take finasteride?

Finasteride is unsuitable for anyone who has experienced a previous adverse reaction to the drug or a similar medication. It is not approved for use in women or children. Finasteride may be contraindicated or taken with caution by patients with liver disease, severe urinary obstruction, and known or suspected prostate cancer.¹⁶

Note that a person who intends to donate blood should plan to stop finasteride six months ahead of a scheduled donation.¹⁷

Potential side effects of finasteride

All medications interact with the body in specific ways to produce negative or positive effects. With finasteride, there may be adverse effects ranging from mild to severe. Common side Finasteride commonly interacts with the body to produce the following side effects:¹⁸ ¹⁹  

• Sexual dysfunction, including impotence, decreased libido, erectile dysfunction, and reduced volume of ejaculation

• Nausea or vomiting

• Breast tissue tenderness or enlargement in men (gynecomastia)

• Rash

• Orthostatic hypotension (positional low blood pressure)²⁰

More serious adverse effects include any of the following:²¹

• Infertility

• Prostate or breast cancer

• Liver disease

• Insulin resistance and type 2 diabetes

• Dry eye disease

• Severe allergic reaction (angioedema, anaphylaxis)

• Depression, suicidal thoughts²²

Overdose

Patients have received one-time doses of finasteride of up to 400mg and multiple doses of up to 80mg per day for three months without noting any adverse effects. However, there have been no reports of clinically significant finasteride overdoses, so their effects and treatment have not yet been established.²³

Allergy information

Allergic reactions to finasteride may manifest as a rash, hives, skin peeling, swelling of the face, mouth, or tongue, vomiting, wheezing or difficulty breathing, rapid heart rate, and anaphylaxis. If you experience any symptoms of an allergic reaction, seek medical attention right away.

Long-term use of finasteride

Finasteride is an effective long-term treatment for BPH. Using it long-term reduces the risks of acute urinary retention and the need for surgery.²⁴

Those taking the drug for AGA will also usually take it long-term, as the effects of the drug stop when discontinued, and any hair growth will reverse.²⁵

In many cases, sexual side effects are reported with the use of finasteride for either indication, including decreased libido, difficulty achieving an erection, and decreased levels of semen. These side effects are usually mild and temporary for most patients. However, in some cases, individuals have reported that symptoms of sexual dysfunction and mood dysregulation remained present even after discontinuing the drug. This has come to be known as post-finasteride syndrome (PFS). Patients taking the lower dose used for treating AGA seem more likely to experience persistent symptoms, but they have also been noted in those being treated for BPH. Studies so far have been inconclusive on the incidence of PFS, and more high-quality, long-term research is needed.²⁶

There is an increased awareness of metabolic consequences related to the long-term use of drugs in this class. Newer studies have found an association with androgen deficiency, leading to dry eye, elevated blood sugar and diabetes, fat accumulation in the liver (non-alcohol-related fatty liver disease or NAFLD), and other liver disease.²⁷

Additionally, the long-term use of finasteride may be associated with an increased risk of high-grade prostate cancer. However, the drug has been shown to reduce the overall incidence of prostate cancer, and it is still unclear whether finasteride influences cancer mortality. Speak with your doctor about the risks and benefits of finasteride use related to prostate cancer.²⁸

Finasteride and pregnancy

Finasteride is not US FDA-approved for any indication in women or children.

Missed doses

If you forget to take a dose of finasteride, skip it and take your next dose as scheduled. Never double your dose to make up for a missed one.

Drug interactions

No severe drug interactions have been noted at this time. However, there are some drugs and supplements to continue with caution or carefully monitor while using finasteride:²⁹ 

• Antibiotics, such as erythromycin, clarithromycin (Biaxin), isoniazid (INH), and rifampin

• Antifungal medications like ketoconazole and itraconazole

• Anti-seizure medications, such as phenytoin (Dilantin), cenobamate (Xcopri), primidone (Mysoline), and carbamazepine (Tegretol)

• Antiviral medications, including etravirine (Intelence), nevirapine, and ritonavir (Kaletra) 

• Bosentan (Tracleer)

• Drugs that treat cancer, such as apalutamide (Erleada), dabrafenib (Tafinlar), lorlatinib (Lorbrena), and others 

• Nefazodone

• St. John's Wort

This is not a complete list of drugs that may interact with finasteride. Make a list of all medications you take to review with your doctor.

Can I drink alcohol while taking finasteride?

Heavy drinking is not advised while taking finasteride as it renders the drug ineffective in its ability to lower the risk of prostate cancer.³⁰ 

What to discuss with your doctor before starting finasteride

When you meet with your doctor about finasteride, be sure to discuss all the symptoms you experience, such as the following:³¹

• Frequent urination (including getting up at night more often to urinate)

• Difficulty starting or stopping urination

• Inability to urinate

• The feeling like you still need to urinate after finishing

• Urinary leakage

• Difficulty obtaining or maintaining erections

• Hair loss³²

• Testicular pain or bulging

Additional topics to review with your prescriber include any of the following that apply to you:³³ ³⁴

• Your medications, prescription and over-the-counter drugs, and supplements that you take regularly or even occasionally

• Allergies to medicines or any previous reactions after taking a medication or supplement

• Your medical history, in particular, liver disease or abnormal liver function tests, diabetes, depression, sexual dysfunction, and prostate cancer or concern, such as an abnormal prostate-specific antigen (PSA) test

• Alcohol use³⁵

Stopping finasteride

It’s essential to note that while finasteride is an effective treatment for BPH, it doesn’t cure the condition. Your symptoms will likely return at some point after you stop taking the medication. Likewise, people taking the drug for hair loss will typically begin losing hair after discontinuing finasteride. If you’re concerned that finasteride isn’t working for you, speak with your doctor about alternative therapies.³⁶

Drug approval history

• 1992: The US FDA approved finasteride for the treatment of BPH.³⁷

• 1997: Finasteride was approved for treating AGA.³⁸

Tips for taking finasteride

Always follow your physician's instructions when prescribed finasteride. It would be best if you also remember the following:

• Take finasteride at around the same time each day.

• Finasteride can be taken with or without food.

• Tell your physician about any side effects you experience.

• Keep up with regular physical exams and lab testing as recommended by your doctor, particularly your prostate-specific antigen (PSA) blood tests to screen for prostate cancer.

• Do not share your medication with others or let anyone else handle your medication.

• Keep your tablets in the pharmacy-provided container with your name and drug information. The container should be stored at room temperature in a dry location to preserve the tablet's coating.

Frequently asked questions

Is finasteride approved for men only?

Yes. The primary use of finasteride is to reduce prostate size in men with BPH. It is also used for the treatment of male pattern baldness. Finasteride has not been approved for any use in women or children.

Is finasteride a steroid?

No, finasteride is not a steroid and does not stimulate hormone production. However, it does prevent testosterone from being transformed into dihydrotestosterone, which reduces prostate growth and potentially shrinks the prostate gland.

Is finasteride suitable for treating hair loss?

Yes, the drug can reduce or reverse male-pattern hair loss.