OverviewDosageSide EffectsInteractionsHalf-Life

Finasteride is currently the 86th  most commonly prescribed drug in the United States. In 2017 alone, there were over nine million prescriptions. Considering how popular this drug is right now, it pays to know a little bit more about this medication, including how long finasteride stays in your system.

 The FDA states the following information regarding finasteride half-life:

Mean effective half-life: Five to six hours in younger cisgender men; over eight hours in cisgender men over the age of 70. 

Time to steady-state: One to two hours

Mean accumulation ratio: 90 percent

Terminal phase half-life: Six hours in cisgender men under the age of 70 and eight hours for those over it

Finasteride has an oral bioavailability of 65 percent and is metabolized by the liver. Ninety percent of the drug is found in plasma proteins. The body then excretes finasteride through urine and feces. 

FAQ

What is the half-life of finasteride?

The half-life of finasteride depends on the age of the person taking the drug. Under the age of 70, for instance, the half-life is 5 to 6 hours. In cisgender men over the age of 70, it is 8 hours for the first dose. After multiple doses, the half-life drops to 4.5 hours. 

How long does finasteride stay in your system?

It has a half-life of 5 to 6 hours for those are under the age of 70. That means it would take approximately 27.5 to 33 hours (5 or 6 hours x 5.5 half-lives) for the body to clear this drug. For cisgender men over 70, the first dose has an 8-hour half-life, with subsequent doses having a half-life of 4.5 hours. That means it could take about 28.25 hours (8 hours + 4.5 hours x 4.5 half-lives) for this group to clear this substance.

Are side effects of finasteride permanent?

There is evidence that some of the side effects from finasteride use may be permanent. Specifically, taking it may lead to reduced libido and erectile dysfunction that continues after you stop taking the drug. One study indicates that this may occur in up to 15.8 percent of finasteride users. 

What happens when you stop taking finasteride?

You should not stop taking finasteride without talking to your doctor first. If you are taking the drug for male pattern baldness, you will start seeing an increase in hair loss within a few months. 

If you take the medication to manage the symptoms of an enlarged prostate, they will return once you stop. 

How common are side effects of finasteride?

The side effects of taking this drug will vary from person to person. Common side effects include:

  • chills,
  • cold sweats,
  • mental confusion, and
  • lightheadedness when standing up. 

Less common side effects include:

  • breast enlargement,
  • bloating,
  • swelling of face, arms, and legs,
  • itching skin,
  • tingling in the hands and feet, and
  • changes in weight. 

In addition, many cisgender men have changes in their sex drive, along with an inability to get an erection. In rare cases, it may affect semen productions and lead to gastrointestinal problems like diarrhea and stomach pain.

Disclaimer: this article does not constitute or replace medical advice. If you have an emergency or a serious medical question, please contact a medical professional or call 911 immediately. To see our full medical disclaimer, visit our Terms of Use page.



Medically Reviewed by:

Paul Bossung

Dr. Paul Bossung, Pharm. D. is a Missouri Board of Pharmacy certified pharmacist. He practices at Mercy Hospital Jefferson in Festus, MO in the inpatient pharmacy.  Paul attended St. Louis College of Pharmacy (STLCOP) and graduated in 2018. He worked at SSM Health Cardinal Glennon for six years as a student pharmacist prior to graduating.OVERVIEWDOSAGESIDE EFFECTSINTERACTIONSHALF-LIFE

Generic Name: finasteride

Brands: Proscar, Propecia, Propecia Pro-Pak

Class: 5-alpha-reductase inhibitors

Availability: prescription required

Molecular Formula: C23H36N2O2

Substance UNII: 57GNO57U7G

What is Finasteride?

Finasteride is a 5-alpha-reductase inhibitor sold under the brand names Proscar and Propecia.

What is Finasteride Used For?

It is used for the treatment of enlarged benign prostate hyperplasia (enlarged prostate) when offered under the brand name Proscar. For benign prostate hyperplasia, the goal is to reduce symptoms associated with the condition, such as difficulty urinating. It takes six or more months to see improvement.

Propecia is for the treatment of male pattern hair loss.

How Does Finasteride Work?

It works by decreasing the production of the hormone dihydrotestosterone (DHT) in the body. DHT can trigger the enlargement of the prostate and even contribute to hair loss. Reduction of this hormone can therefore prevent prostate enlargement as well as decrease hair loss. 

How Long Does it Take for Finasteride to Work?

How long it takes to work depends on the form of the drug taken. For hair growth, it can take three to four months before the medication begins to affect. It will be six to nine months before there is significant hair regrowth.

For benign prostate hyperplasia, it takes six or more months to see improvement in relevant symptoms.

Do Not Use Finasteride If:

There are several situations where this medication may not be the right choice for you. According to the U.S National Library of Medicine, the following should not use finasteride:

  • Those who are pregnant or breastfeeding
  • Cisgender men who have had breast cancer
  • Anyone experiencing suicidal thoughts
  • Anyone with liver problems
  • Those with high-grade prostate cancer
  • People with a known allergy to 5-alpha reductase inhibitors

Please note that this list may not be complete, and there may be other situations where finasteride use is not advisable.

Disclaimer: this article does not constitute or replace medical advice. If you have an emergency or a serious medical question, please contact a medical professional or call 911 immediately. To see our full medical disclaimer, visit our Terms of Use page.


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