How Long Does Finasteride Stay in Scalp Tissue?

Article Summary

Finasteride is an FDA-approved hair loss treatment, with clinical studies showing that the drug lowers levels of the hormone dihydrotestosterone (DHT) by 60-70%, and in doing so, improves outcomes of androgenic alopecia (AGA) for 80-90% of the men who try to the drug. But how long do finasteride’s effects last after quitting? The answer depends on how long finasteride remains active in scalp tissues, and that answer depends on the drug’s (1) terminal half-life, (2) tissue dissociation timings, and (3) biological half-life. This article explores the evidence, as well as clinical studies elucidating alternate finasteride dosing schedules that can dramatically cut down on drug exposure, and perhaps without risking any hair gains.

Full Article

After quitting finasteride, many users wonder how long they have until:

1. The drug leaves the bloodstream
2. Hormone levels to return to baseline
3. When hair loss will resume

The answers vary slightly from person-to-person, but all relate to how finasteride behaves in the body: its distribution, saturation, tissue binding capacity, metabolism, and excretion. These terms are all related to the pharmacokinetics.

In this article, we’ll dive into the pharmacokinetics of finasteride to answer how long finasteride stays active in the scalp skin. In doing so, we’ll also reveal an alternate dosing strategy that some finasteride users employ to maintain hair gains, but potentially lower their risk or magnitude of side effects.

What Is Finasteride?

Finasteride is an FDA-approved drug for androgenic alopecia (AGA) – one of the world’s most common hair loss disorders in adults.

Finasteride works by blocking the formation of an enzyme called 5α-reductase, which transforms free testosterone into dihydrotestosterone (DHT). An abundance of evidence shows that DHT is causally associated with hair growth cycle disruptions, hair thinning, and hair loss from AGA. Clinical studies also show that finasteride can therapeutically lower DHT and, in doing so, improve AGA outcomes in 80-90% of the men who use it.^[1]https://pubmed.ncbi.nlm.nih.gov/9777765/

For these reasons, many consider finasteride to be the gold-standard treatment for AGA.

Unfortunately, as with all drugs, finasteride is also causally linked to side effects in a portion of men and women trying the drug. It’s also contraindicated in women who are planning to become pregnant, already pregnant, and/or breastfeeding – with debate over whether men should stop finasteride prior to conceiving.

For these reasons, some finasteride users choose to stop using the drug for a variety of reasons: (1) troubleshoot side effects, (2) conceive without finasteride detectable in the semen, or (3) just take a break due to travel.

What Happens When Someone Quits Finasteride?

Clinical studies on finasteride also show that once the drug is paused, hair loss eventually presumes and converges back to where a user would’ve been had they never started the drug in the first place.

Just see this chart from a two-year clinical study on men using 1 mg daily of finasteride.^[2]https://pubmed.ncbi.nlm.nih.gov/9777765/ In the group labeled Fin → Pbo, users were given finasteride for the first year, and then unknowingly switched into the placebo group from year one to year two. As we can see, hair counts improve up until year one, then decline below baseline by the end of year two:

For these reasons, the manufacturers of finasteride often warn users that after quitting the drug, hair loss will resume, and within 3-12 months, any hair gains maintained by the drug will be lost.

But just how long after quitting finasteride will it take for hair loss to resume? The question depends entirely on finasteride’s biological half-life in scalp skin tissues. More specifically, it depends on how long finasteride can continue suppressing DHT levels in the scalp, even after a user has stopped taking it.

Finasteride: Effects On Scalp DHT

To reiterate, DHT is the hormone causally linked to hair loss from AGA. Finasteride can therapeutically lower DHT levels by ~70% throughout the body. At this level of suppression, AGA often stabilizes and some hair regrowth can be achieved.^[3]https://pubmed.ncbi.nlm.nih.gov/10495374/

However, when it comes to scalp hair regrowth, DHT reduction is not as important throughout the body as it is in the scalp.

After all, several studies from the 1980’s and 1990’s suggest that up to 80% of the DHT found in balding scalps is manufactured at the site of the hair follicle – more specifically, the outer root sheath, dermal papillae cell cluster, and even the mesodermal sheath.^[4]https://www.ncbi.nlm.nih.gov/books/NBK557634/^[5]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6459338/^[6]https://dm5migu4zj3pb.cloudfront.net/manuscripts/113000/113003/JCI87113003.pdf

Therefore, when many people ask, “How long does finasteride stay in the bloodstream?”, they’re mostly asking the wrong question. Instead, they should be asking, “How long does finasteride continue to impact scalp DHT levels – even after quitting the drug?”

The answer to that question depends on finasteride’s:

1. Terminal half-life. In other words, how long will it take for 50% of the finasteride ingested to get metabolized and sent to the digestive tract for excretion?
2. Tissue dissociation. In other words, how long does it take for active finasteride to “unbind” to those tissues and re-enter circulation and/or get sent to the digestive tract for excretion?
3. Biological half-life. In other words, given finasteride’s terminal half-life and tissue dissociation timing, how long will it take for 50% of the drug to stop having its biological impact (i.e., lowering DHT levels)?

The answers will help provide a more nuanced perspective on just how long finasteride stays active in the scalp, and how long someone has before hair loss might presume.

Finasteride Pharmacokinetics

According to pharmacokinetic studies, here’s some key information about finasteride:^[7]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3481923/

• Terminal half-life: 5-7 hours, with slightly longer half-lives in older populations
• Tissue dissociation: 4-5 days, meaning that finasteride can remain attached and/or bound to organs for longer than its half-life – which potentiates the drug having a longer-lasting effect than its terminal half-life might suggest
• Biological half-life: 14-30 days, mainly due to its tissue dissociation timings after reaching peak drug distribution and saturation throughout the body (which can happen after only a handful of 1 mg daily ingestions of the drug)

How Long Does Finasteride Impact Scalp DHT Levels?

For most people, finasteride appears to still appreciably lower scalp DHT levels for up to 30 days after quitting the medication.

This was best illustrated in a clinical study measuring blood DHT levels before, during, and after use of finasteride and dutasteride versus a placebo group.^[8]https://academic.oup.com/jcem/article/89/5/2179/2844345

Again, the answer is due to how finasteride is stored in organs like the skin. Studies suggest that once finasteride binds to cells within the skin, it has a tissue dissociation timing of 4-5 days.^[9]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3481923/

In other words, it can take 4-5 days before the finasteride that has bound to skin cells dissociates from those tissues and reenters the bloodstream for metabolism and excretion.

Interestingly, once finasteride users understand these pharmacokinetics, they can actually use them to their advantage in order to (1) temporarily quit finasteride (if needed), while also (2) preserving hair gains from the drug.

Taking Advantage Of Finasteride’s Tissue Dissociation Timings

Given the relatively long biological half-life of finasteride, many users have wondered, “Can I temporarily quit the drug for any reason, and without sacrificing any of my hair gains?”

So far, clinical studies seem to suggest it’s possible – at least within short-enough cessation periods.

One clinical study on men showed that after one year of taking finasteride, men who switched to a 30-day on, 30-day off dosing schedule for year two achieved comparable hair regrowth to those who continued taking finasteride daily.^[10]https://jaad.org/retrieve/pii/S0190962220319289

In other words, these men were able to cut their drug exposure by 50% throughout year two – and take a total  of 6 months off the drug – without sacrificing any hair gains versus those taking the drug daily throughout that same year.

This is, again, due to finasteride’s biological half-life – which relates to its terminal half-life and tissue dissociation timings.

Anecdotally, many members of our community have found that taking a 2- to 3-week break from finasteride to troubleshoot side effects, or to fully disconnect during family vacations, does not seem to adversely impact their hair gains. So, at least within our community, we have a number of people to corroborate this clinical evidence with real-world experience.

Beyond a full month of quitting, it’s very likely that scalp levels of DHT fully return to baseline and that hair loss resumes. So, keep this in mind before deciding to experiment with different finasteride dosing schedules.