5-alpha reductase inhibitors: Uses, common brands, and safety info

5-alpha reductase inhibitors are a class of medications prescribed for the treatment of benign prostatic hyperplasia (BPH) and androgenic alopecia (male pattern hair loss). Currently, finasteride and dutasteride are the only FDA-approved medications in this class. Both medications work in similar ways to block the 5-alpha reductase enzyme and reduce the conversion of testosterone to dihydrotestosterone (DHT). The male hormone DHT is believed to be involved with the development of BHP and hair loss in men. 

Continue reading to learn more about 5-alpha reductase inhibitors, how they work, and their side effects.

What are 5-alpha reductase inhibitors?

5-alpha reductase inhibitors are often prescribed to treat an enlarged prostate and hair loss in men. These medications help relieve BPH symptoms, such as frequent urination, difficulty urinating, pain during urination, and a frequent urge to urinate. 5-alpha reductase inhibitors can also help prevent hair loss while promoting the growth of new hair. 

This class of drugs is typically administered as a daily oral tablet. Finasteride is available as a brand and generic drug. It can be taken as a 1 mg or 5 mg tablet depending on the condition being treated. Propecia is the brand name of finasteride approved to treat androgenetic alopecia as a 1 mg daily tablet. Proscar is the brand name of finasteride approved to treat BPH as a 5 mg daily tablet. 

Dutasteride is available as a brand and generic medication. The brand name of dutasteride is Avodart, and it comes as a 0.5 mg oral capsule that is usually taken once daily. Dutasteride is sometimes prescribed as a combination pill that also includes tamsulosin. Also known by its brand name Flomax, tamsulosin is an alpha-blocker medication that helps relax the muscles of the prostate and opening of the bladder. Jalyn, the combination dutasteride-tamsulosin pill, helps improve the symptoms of BPH.

How do 5-alpha reductase inhibitors work?

5-alpha reductase inhibitors work by blocking 5-alpha reductase, an enzyme that promotes the conversion of testosterone into dihydrotestosterone (DHT). By blocking this enzyme, 5-alpha reductase inhibitors help reduce the production of DHT. Androgens like testosterone and DHT are the male sex hormones that bind to androgen receptors throughout the body and are involved with several processes. Testosterone is produced by the gonads and adrenal glands, and it is involved with increased muscle mass and growth during puberty in males. Testosterone is converted into DHT, an androgen that is involved with the regulation of the hair growth cycle as well as the growth of the prostate.

An enlarged prostate, or BPH, is a common problem in men with 20% of men in their 40s and up to 60% of men in their 60s living with it. The prevalence of BPH increases with age. In someone with BPH, DHT can build up in the prostate gland and bind to prostatic androgen receptors, which can lead to enlargement of the prostate. 5-alpha reductase inhibitors can cause a decreased prostate size to make it easier to urinate and relieve pain during urination. 

Around 50% of men and women live with hair loss, or pattern baldness. DHT can bind to hair follicles and cause them to shrink, which can eventually lead to complete hair loss. Clinical trials have shown that 5-alpha reductase inhibitors can cause an increase in hair count within a year. 

What are 5-alpha reductase inhibitors used for?

5α-reductase inhibitors are FDA approved to treat specific conditions in men. However, they have also been used off-label to treat hirsutism in women. They are also sometimes prescribed to transgender women because of their ability to block the production of androgens. 

• Benign prostatic hyperplasia (BPH)

• Androgenic alopecia (hair loss)

• Hyperandrogenism

• Hirsutism

• Hormonal treatment in transgender women

Types of 5-alpha reductase inhibitors

Finasteride

Studies have shown that finasteride can reduce DHT levels by up to 70% in the blood and up to 90% in the prostate gland. Finasteride primarily blocks the type II and type III 5-alpha reductase enzymes. The different types of 5-alpha reductase enzymes are found throughout the body; for example, type II 5-alpha reductase is primarily found in the hair follicles and prostate while type I 5-alpha reductase is found in the sweat and sebaceous glands. 

Dutasteride

Dutasteride can decrease DHT levels in the blood by up to 99%. This is because dutasteride blocks all types of 5-alpha reductase in the body: type I, type II, and type III alpha-reductase. Because it decreases the production of DHT more than finasteride, dutasteride may be more effective than finasteride. 

Who can take 5-alpha reductase inhibitors?

Adults

5α-reductase inhibitors are approved to treat BPH and hair loss in men. They are not FDA-approved for use in women. These medications are typically taken once daily with or without food to relieve lower urinary tract symptoms of BPH or slow hair loss. In some cases, 5-alpha reductase inhibitors may be prescribed off-label to treat hyperandrogenism that leads to excessive hair growth in women (hirsutism). They are also sometimes prescribed off-label as hormonal treatments for transgender women. 

Seniors

Older adults may also be prescribed 5-ARIs. It is common for older men to experience BPH or male pattern hair loss since the incidence of these conditions increases with age. However, it’s important for older adults to consult a healthcare provider to ensure these medications may be appropriate. 

Children

Finasteride and dutasteride are not approved for use in children under the age of 18. 

Are 5-alpha reductase inhibitors safe?

5-alpha reductase inhibitors are generally safe and can improve quality of life when used appropriately. There are no significant concerns for toxicity and overdose related to 5-alpha reductase inhibitors. Clinical trials have shown that there is a low risk of adverse effects associated with an overdose of a 5-alpha reductase inhibitor. 

Recalls

Finasteride Plus - 05/11/2020

Restrictions

The use of 5α-reductase inhibitors is not recommended in children. DHT is an important hormone involved in the sexual development of children. 

5-alpha reductase inhibitors are contraindicated in women who are pregnant or who are planning to become pregnant. These medications can affect a male unborn baby and cause problems in the development of the male sexual organs. Pregnant women should also avoid touching or handling finasteride tablets or dutasteride capsules.

People who have a known sensitivity to any ingredients found within 5-alpha reductase inhibitor medications should avoid taking a 5-alpha reductase inhibitor. Otherwise, there may be an increased risk of hypersensitivity reactions including skin reactions. 

Are 5-alpha reductase inhibitors controlled substances?

No, 5-alpha reductase inhibitors are not controlled substances.

Common 5-alpha reductase inhibitors side effects

The most common side effects of 5-alpha reductase inhibitors include:

• Decreased sex drive

• Decreased ejaculatory volume

• Erectile dysfunction

• Gynecomastia (enlargement of breast tissue in men)

Dutasteride is sometimes administered as a combination pill that includes tamsulosin. This combination pill, Jalyn, has been reported to cause orthostatic hypotension, or low blood pressure, that occurs when standing up from a lying or sitting position. Other side effects of Jalyn include dizziness and weakness. 

Some men may experience a decrease in prostate-specific antigen (PSA) levels while taking a 5-alpha reductase inhibitor. Baseline PSA levels may need to be measured prior to the start of treatment. PSA levels may then need to be monitored throughout treatment to evaluate the effects of the drug. 

An increase in PSA levels while on treatment with a 5-alpha reductase inhibitor may indicate the presence of prostate cancer. The use of 5-alpha reductase inhibitors can lead to an increased risk of high-grade prostate cancer. 

This is not a complete list of side effects, and others may occur. Consult a healthcare provider for other possible side effects, drug interactions, warnings, and precautions associated with 5-alpha reductase inhibitors. Before taking a 5-alpha reductase inhibitor, tell your doctor about any medical conditions you may have and other medications you may be taking, including prescription drugs, over-the-counter medicine, and herbal supplements.  

In rare cases, side effects may not resolve with continued use of a 5-alpha reductase inhibitor. A healthcare provider should be consulted if side effects persist or worsen. 

5-alpha reductase inhibitors can cause fetal abnormalities in women who are pregnant.  

How much do 5-alpha reductase inhibitors cost?

5-alpha reductase inhibitors are available in both generic and brand-name forms. Medicare and insurance plans generally cover the generic forms of these medications. Copays with insurance can vary depending on the plan, the plan’s formulary, and the medication prescribed. 

Without insurance, the cost of a prescription for finasteride or dutasteride can be high. A savings card, like the SingleCare prescription discount card, may help lower the cash price of the medication. The price with a SingleCare card may also be preferred over the copay cost with insurance. Consult an insurance provider or pharmacy for more information about the cost of 5-alpha reductase inhibitors.