How Long Does Finasteride Stay in the Bloodstream?

Article Summary

Oral finasteride is an excellent option for men wanting a ‘hands-free’ approach to hair maintenance. However, some men decide to temporarily or discontinue use of the drug to troubleshoot side effects, conceive, or even start donating blood. Under these circumstances, how long does finasteride stay in the bloodstream after someone stops taking it? The answer depends on finasteride’s terminal half-life, tissue dissociation timings, and more. This article explores the science behind finasteride’s pharmacokinetics to explain just how long finasteride might remain in the system or bloodstream, even after quitting.

Full Article

Oral finasteride is a gold-standard treatment option for men wanting a low-effort approach to hair maintenance. The drug is FDA-approved for androgenic alopecia (AGA) – with two-year studies showing that 1 mg daily of finasteride might slow, stop, or partially reverse AGA progression in 80-90% of men using the drug.^[1]https://pubmed.ncbi.nlm.nih.gov/9777765/

But what happens when someone decides to stop using finasteride? How long does the drug remain in the system? After withdrawal, how long does the drug continue to impact hormones like dihydrotestosterone (DHT)?

In this article, we’ll explore the scientific papers that have attempted to answer these questions, and provide step-by-step instructions for what to expect should you decide – for any reason – to withdraw from finasteride.

Why Might Someone Stop Using Finasteride?

There are three main reasons someone might withdraw from finasteride use:

1. Experiencing side effects. In this case, withdrawing can help troubleshoot if those side effects are related to the drug or perhaps something else in their life.
2. Trying to conceive. Under these circumstances, a user may not want to risk having the drug interfere with their ability to do so or the health of the baby. (Note: while men have the option to temporarily withdraw from finasteride during windows of conception, the drug is contraindicated in women who are pregnant, planning to become pregnant, or breastfeeding.)
3. Not seeing enough benefit. Unfortunately, finasteride doesn’t work for everyone, which may lead to drug withdrawal for those not seeing desired results.

In cases of side effects and conception, withdrawal might be temporary.

For instance, men experiencing sexual dysfunction might withdraw from finasteride to gauge if it’s the drug causing the side effect, or perhaps something else in their life (like poor dietary, lifestyle, and/or environmental habits). Men who want to conceive might temporarily withdraw from finasteride to ensure that none of their semen is influenced by finasteride during the period of conception, after which they can then hop back on the drug.

However, for those who are having trouble tolerating finasteride – or for those who aren’t getting any results from the drug – finasteride withdrawal might be more permanent. In these cases, users might find better success by switching to dutasteride, adding in adjuvant therapies like microneedling and/or minoxidil, or exploring if their hair loss is actually androgenic or perhaps caused by other factors – like hypothyroidism.

Under these circumstance, how long does finasteride stay in the bloodstream after we stop taking it? How long until the effects of the drug reverse?

After Quitting, How Long Does Finasteride Stay in the Bloodstream?

The answer depends on (1) how long it takes for the body to metabolize finasteride, and (2) whether you’ve taken enough finasteride to reach steady-state saturation levels throughout the body.

The term most often used to describe drug metabolism is terminal half life. That’s the amount of time it takes for the body to metabolize 50% of a drug dose.

According to pharmacokinetic studies, finasteride has a terminal half-life in the bloodstream of 5-7 hours. This means that it takes 5-7 hours before half of the drug is metabolized from the circulatory system and sent for excretion – where finasteride is primarily excreted through bile and urine.^[2]https://pubmed.ncbi.nlm.nih.gov/8846625/

So, if you took 1 mg of finasteride one time, your body would probably metabolize, inactivate, and excrete all of that finasteride within a 2-3 days.

However, taking 1 mg one time isn’t how most people use finasteride. So, what about real-world usage cases – where someone takes 1 mg of finasteride daily for weeks, months, or years?

If this person stops, how long would it take for the drug to clear the system and for the drug’s effects to go away?

With repeated doses, finasteride reaches a saturation point throughout the body. This is where the drug travels throughout the bloodstream, gets distributed throughout other organs and tissues, and after that distribution reaches its peak, blood levels of finasteride reach a steady-state.

In other words, there’s an equilibrium reached for the amount of new finasteride coming into the body, and the amount of finasteride getting metabolized and excreted by the body. And we can measure this equilibrium by measuring steady-state plasma levels (i.e., blood levels) of finasteride as someone takes repeat doses.

For most people, steady-state plasma levels of finasteride are reached within just a few days.^[3]https://pubmed.ncbi.nlm.nih.gov/24012200/ And once that occurs, the “equation” for finasteride’s full elimination changes.

Why? Because now finasteride’s excretion isn’t just dependent on its terminal half-life – or how long it takes for 50% of that finasteride to get metabolized from the blood. Now, the equation must also take into account how long it will take for all finasteride that has been stored in other tissues and organs – like the skin and prostate – to dissociate from those sites, re-enter the blood stream, and get metabolized.

According to pharmacokinetic studies, finasteride has a tissue dissociation timing of 4-5 days.^[4]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3481923/ Because of this, finasteride’s full excretion from the body (and bloodstream) can actually take a bit longer than a few days.

In fact, withdrawal studies on finasteride have demonstrated that despite its terminal half-life of 5-7 hours, it still takes ~30 days for blood levels of dihydrotestosterone (i.e., DHT) to return back to baseline after someone quits the drug.^[5]https://academic.oup.com/jcem/article/89/5/2179/2844345 Just see this chart comparing drug withdrawal from finasteride and dutasteride versus placebo – and the number of weeks it takes for the finasteride group to return to baseline levels of serum DHT.

 

Moreover, after quitting, former finasteride users will typically lose any hair gains from the drug within 3-12 months.

So, to summarize:

• Finasteride’s terminal half-life is 5-7 hours. This is the amount of time it takes for 50% of a drug’s dose to be metabolized and sent for excretion.
• Finasteride’s biological half-life is 14-30 days. This is the amount of time it takes for the biological effects of a drug to fully reverse. In the case of finasteride, this is a return to baseline levels of DHT. This takes longer than a drug’s terminal half-life, because the equation for biological half-life involves not only a drug’s terminal half-life, but also the drug’s saturation levels and its tissue dissociation timings.

How To Take Advantage Of Finasteride’s Terminal & Biological Half-Lives

Because of the mismatch between finasteride’s terminal half-life and biological half-life, users of finasteride who withdraw from the drug don’t immediately lose their hair. Instead, it usually takes ~3 months for hair loss following finasteride withdrawal to presume.

In fact, one clinical study found that after one year of finasteride use, men who switched to 30 days-on, 30 days-off finasteride use were no worse off than men who continued taking the drug every day.^[6]https://www.jaad.org/article/S0190-9622(20)31928-9/fulltext

This is, again, because of the difference in finasteride’s terminal and biological half-lives. And with this knowledge, finasteride users who intend to temporarily withdraw from the drug can leverage these differences to their advantage.

For example, say a male would like to conceive with their partner, but they don’t want finasteride to potential impact their semen parameters during the window of conception. This user can:

1. Withdraw from finasteride. After 30 days, the drug should be fully out of the system and all biological effects should return to baseline.
2. Conceive with their partner. Technically speaking, they have a 1-2 month window after that 30-day washout period whereby hair gains from finasteride should remain preserved.
3. Hop back on finasteride. After conception is complete, this male can restart finasteride prior to hair loss reinitiating – so long as they were able to conceive during that 1-2 month window following their finasteride washout period.

The same approach can be taken with troubleshooting side effects, or deciding to leave finasteride at-home while traveling short-term, or any other reason you might want to temporarily hop off the drug.

Those experiencing side effects can potentially minimize them by switching to a topical formula. Just be aware that topical finasteride can enter the bloodstream, too, depending on the percent active ingredient, the amount applied, and the length of time the solution is left on the scalp.