Finasteride: What is it used for? How does it work? Dosage, Side Effects, Interactions and Warnings

It is a drug or antiandrogen agent prescribed by doctors to treat male pattern baldness and benign prostatic hyperplasia.

Some of the brands sold with finasteride include Proscar, Fincar, Propecia, Finpecia, Finast, Finax, Finara, Finalo, and Prosteride.

What is finasteride used for?

It is used to improve prostate symptoms and decrease your need to urinate. Proscar (finasteride) reduces the size of the prostate and relieves the symptoms of an enlarged prostate, but it can cause a loss of sexual desire or excitement when you first start taking this medication.

How does it work?

Finasteride works by inhibiting type II 5-alpha reductase, the enzyme that converts testosterone to dihydrotestosterone (DHT).

This converted form of testosterone stimulates the development of the penis, testes, scrotum, and other male sexual characteristics such as body and pubic hair. DHT also promotes the growth of the prostate.

DHT is the hormone responsible for androgenetic alopecia (male pattern baldness). DHT binds to the hormone receptors in the hair follicles, causing them to shrink and eventually stop producing hair.

In people genetically predisposed to male pattern baldness (androgenic alopecia), DHT binds to the receptors in the hair follicles on the top of the scalp. When the hormone DHT acts on these follicles, they contract and gradually lose the ability to develop thick, healthy hair.


As a result, the person’s hairline becomes thin and backward. The hair follicles on the back and side of the head are genetically resistant to DHT, which explains the typical pattern of male pattern baldness.

Dihidrotestosterona (DHT)

DHT is an essential male sex hormone, about five times more potent than testosterone.

Therefore, to put it simply, finasteride reduces the hormone levels responsible for hair loss.

If you have already researched treatments for hair loss, you may have heard of another name: Propecia.


Propecia is the brand name of 1 mg finasteride tablets. This dosage is prescribed as a daily pill to prevent hair loss.

Finasteride is also available in 5 mg tablets (trademark Proscar). This dosage is prescribed to treat benign prostatic hyperplasia. However, patients with hair loss can often acquire it off the label and divide the tablet to reduce costs.

Taking 1 mg of finasteride daily reduces the levels of DHT in the scalp by about 70%.

This is enough to stop, delay and even reverse hair loss for most users.

It is approved by the FDA and shown in numerous studies to be an effective treatment against hair loss.

Side effects

It has proven to be a highly effective hair loss treatment. However, like almost all medications, it has the potential to cause side effects.

Among the side effects listed by the manufacturer of Propecia are:

  • Erectile dysfunction.
  • Decrease in libido
  • Difficulty reaching orgasm.
  • Abnormal ejaculation
  • Swelling or tenderness in the breasts.
  • Dizziness.

Adverse sexual events are more noticeable in younger men. Several side effects have improved or resolved entirely once Propecia treatment is stopped. In contrast, others may continue to affect the patient for several months or even years.

In some cases, the sexual function never returns to normal.

Other side effects

  • Allergic reactions: rash, itching, hives, and swelling of the lips and face.
  • Increase and tenderness of the breasts.
  • Depression .
  • Testicular pain
  • Male infertility or poor semen quality.
  • Male breast cancer.
  • Prostate cancer.

The medication also contains a warning that menage 55 and older who take Propecia may have an increased risk of an aggressive type of prostate cancer. The sign is based on the dose to treat the enlarged prostate, five times higher than the dose used for hair loss.

Prostate cancer screening

High-grade prostate cancer is highly aggressive and proliferates, often spreading to other areas, such as lymph nodes and bones. In addition, high-grade prostate cancer cells are large, difficult to treat, and reappear more frequently than low-grade and intermediate-grade prostate cancers.

Although the cancer risk appears to be low, the FDA distributed the advertisement to inform physicians and patients about the safety reviews of warning and caution labels for this class of medications.

The evidence of increased risk comes from two large clinical trials: the seven-year Prostate Cancer Prevention (PCPT) trial and the four-year reduction trial of the Dutasteride of Prostate Cancer Events (REDUCE).

Both trials sought to determine if finasteride could be used to reduce the risk of prostate cancer.

Although PCPT and REDUCE did decrease the incidence of lower-risk prostate cancer forms, it was found that patients in both trials had an increased risk of high-grade prostate cancer.

Related drugs

Propecia is not the only 5α-reductase inhibitor currently available. Two others, Proscar and Avodart, are also designed to prevent the conversion of testosterone to DHT. However, unlike Propecia, Proscar and Avodart are not indicated to treat male pattern baldness.

They are approved to treat BPH in men with an enlarged prostate and help control the condition’s urinary symptoms.


Presentation: Proscar Tablets.

Proscar also uses finasteride, but it contains five times the dose of Propecia.

Proscar, like Propecia, is a 5-alpha-reductase inhibitor drug that contains the active ingredient finasteride.

The FDA approved the drug in 1992.

Proscar contains five times the dose of finasteride used in Propecia and offers a similar range of possible side effects.

In a four-year placebo-controlled clinical trial called Proscar Long-Term Efficacy and Safety Study (PLESS), the safety of 3,040 patients between the ages of 45 and 78 with symptomatic BPH and enlarged prostate was evaluated.

Of these patients, 3.7 percent were treated with Proscar, and 2.1 percent were given a placebo and discontinued treatment due to adverse reactions to sexual function.

In another study of patients who took Proscar alone or combined with doxazosin (another 5-alpha-reductase inhibitor), four out of 1,554 patients developed breast cancer. This rate is approximately 200 times the rate of breast cancer in the general population.


Presentation: Avodart Tablet

Unlike Propecia, Avodart uses dutasteride as an active ingredient.

Although it has an active ingredient different from Propecia and Proscar, Avodart is also designed to block the enzyme that converts testosterone to DHT.

Like finasteride, dutasteride, the active ingredient in Avodart, is also associated with decreased libido, decreased amount of semen released during sex, impotence, and tenderness or enlargement of the breasts. Avodart may also increase a patient’s risk of developing prostate cancer.

The FDA first approved Avodart in 2001 for the drug available in 0.5 mg soft gelatin capsules once a day.


While finasteride has no known drug interactions, dutasteride may interact with certain anti-HIV medications, such as ritonavir; certain medicines for blood pressure and angina, such as amlodipine; and certain antibiotics, such as azithromycin.

Taking dutasteride at the same time that any of these medications can slow down the breakdown of dutasteride in the liver, causing more drugs to remain in the body.

As with Propecia, women and children should not take Avodart. The medication can cause congenital disabilities if a woman is exposed to it during pregnancy.


Propecia is not approved for use in women and children. Women should not handle crushed or broken Propecia tablets when they are pregnant or may be pregnant due to a possible risk to a male fetus.

DHT is a hormone necessary for the normal development of the male genitalia. As a result, if a pregnant woman receives finasteride, the drug can cause abnormalities in the external genitalia of a male fetus, according to the FDA.

Propecia and other 5-alpha-reductase inhibitors may increase the risk of high-grade prostate cancer, the deadliest form of prostate cancer.

As an information

The FDA (Food and Drug Administration): It is a governmental agency of the United States established in 1906 with the Federal Law of Food and Drugs approval.

Currently, the agency is divided into five centers, which oversee most of the organization’s obligations related to food, medicine, cosmetics, animal feed, dietary supplements, medical devices, biological products, and blood products.