We have always been told that the hormone dihydrotestosterone (DHT) is by far the dominant cause of male pattern hair loss (aka androgenetic alopecia). However, numerous other hormones have positive and negative effects on scalp hair growth. I only realized this fully after a new study found yet another hormone to have an impact on hair growth. See the bottom of this post for a full list.
Serotonin and Hair Loss
A July 2025 publication by the renowned Dr. Junji Fukuda’s team in Japan found that serotonin (5-hydroxytryptamine, 5-HT) activates hair growth related genes in dermal papilla (DP) cells. Serotonin is both a neurotransmitter and a hormone. It is often confused with dopamine, since both are neurotransmitters, hormones and feel good molecules. Note that an older 2014 study also found that 5-HT plays a role in regulating hair pigmentation and stress-induced depigmentation.
In this study, the authors mention that circulating serotonin is mainly produced via intestine-microbiome interactions. They also briefly discuss how the microbiome produces various factors and metabolites that influence hair growth and hair regression. This has become an interesting new area of hair loss research, including via related research into the use of live biotherapeutic products to treat hair and skin disorders.
Serotonin, hair growth and dermal papilla-intestine interactions. Source: Scientific Reports, July 2025.
Circulating Hormones and their Influence on Dermal Papilla Cells
One paragraph in the above study in regards to various hormones and their effect on hair growth caught my eye. Especially since I have covered a few of them on this blog (see highlighted links below) without realizing that the number has built up.
“Multiple circulating hormones influence DP cells. For example, dihydrotestosterone shortens the anagen phase of DP cells, while increased estrogen levels (e.g., during pregnancy) spur additional hair growth. Likewise, oxytocin and cortisol exert opposing effects on DP cells and hair growth, the former activating growth factor secretion (stimulatory) and the latter decreasing Gas6 expression (inhibitory). The circadian hormone melatonin promotes hair regeneration via activating Wnt signaling in DP cells. Research on novel hair growth-promoting hormones has accelerated worldwide in pharmaceutical and cosmetic industries, largely targeting these hormones.”
Sublingual Minoxidil for Hair Loss: Phase 3 Trials Beginning
Dermatologist and Professor Dr. Rodney Sinclair is recruiting 150 Australian volunteers for Phase 3 clinical trials of his proprietary sublingual minoxidil tablet. Per Dr. Sinclair, over the course of 15 years at Sinclair Dermatology, they have treated around 30,000 patients with this medication in different doses. They have thus managed to hone and optimize their technique. Key quote:
“If the treatment receives regulatory approval, it is anticipated to be available on the market within two years. If we can get this through the regulatory pathways and make it available in pharmacies, it may well be that baldness becomes something that is perfectly optional.”
I do not buy the “perfectly optional” part of the quote at all. But it is possible that the hair growth results from sublingual minoxidil turn out to be superior to that from oral minoxidil.
Note that Sinclair Dermatology also prescribes low-dose oral minoxidil via its “Hairy Pill“.
Also of note, in a June 2025 study from Sinclair Dermatology, it was reported that low-dose sublingual minoxidil (SLM) increased hair fiber diameter in a dose dependent manner.
“Among men receiving SLM 0.45 mg, 1.35 mg and 4.05 mg, the mean increase in fibre diameter was -2 µm (SD 1 µm), 3 µm (SD 1 µm) and 6 µm (SD 1 µm), respectively.”
April 9, 2018
Sublingual Minoxidil for Hair Loss
Since 2022, low-dose oral minoxidil for hair loss (LDOM) has become increasingly popular. These pills or tablets are directly ingested. However, a potentially superior method is to take oral minoxidil sublingually (via administering under the tongue).
The biggest proponent of this method is Sinclair Dermatology in Australia, led by Dr. Rodney Sinclair. His clinic is undertaking clinical trials for sublingual minoxidil to treat male and female pattern hair loss.
Earlier today, a reader named “Chris” posted an interesting video about a new hair loss treatment from Australia that entails putting some kind of dissolvable listerine-style strip underneath the tongue. Chris asked me for my opinion about this treatment.
At first, I thought that this seemed like yet another scam since the title of the video includes the word “breakthrough”. Moreover, the video does not even mention what ingredients are in the sublingual strip or patch itself.
However, since the famous Australian dermatologist Dr. Rodney Sinclair appears in the video, I decided to conduct further research. Dr. Sinclair is an extremely well respected researcher in the hair loss world. In the above video, he is honest and clearly says that this treatment will not bring back hair in totally bald scalps.
Having said that, so far it seems that the results from this treatment on people who have moderate levels of balding have been very positive. And this got me curious about what magic concoction was in the strip itself.
Clinical Trial
I did not have to conduct much further research to figure out what this new potential breakthrough for hair loss patients entailed. On Dr. Sinclair’s blog, the latest post from today discusses a new clinical trial they are conducting that is recruiting both men and women. Volunteers will be treated with low-dose oral minoxidil that will be given as a sublingual tablet (which will dissolve under the tongue).
I would not be surprised if the tablet is actually the strip/patch that was shown in the video I posted earlier. It would be very uncomfortable to put an actual tablet underneath the tongue and wait for it to dissolve, unless the dissolution happened very rapidly. On the other hand, a strip would be much easier to keep in place underneath the tongue for a longer period of time.
If you live in Australia or in the nearby vicinity, perhaps it is worth volunteering for these trials. Today I finally learnt the definition of “sublingual”.
Oral Minoxidil versus Sublingual Minoxidil
Many people are wondering if sublingual minoxidil is really more effective than oral minoxidil at growing hair? Dr. Sinclair and scientists from Brazil published a paper in December 2024 that is titled:
“Sublingual minoxidil 5 mg versus Oral Minoxidil 5 mg for male androgenetic alopecia: A double-blind randomized clinical trial.”
One brief online summary of this paper suggests that the results are comparable. I am unable to find the full contents of this paper to provide my own summary.
The below video provides a good comparison of sublingual vs oral minoxidil for hair loss:
Newer Updates
Update: July 2020 — From Sinclair Dermatology comes a new case series report of 64 patients taking sublingual minoxidil (0.45 mg per day) for pattern hair loss.
Update: March 2021 — An excellent video presentation on sublingual minoxidil from Dr. Bevin Bhoyrul from Sinclair Dermatology:
Update: September 2021 — Sinclair Dermatology’s clinical trial of 40 male and female patients receiving sublingual minoxidil (SM) for androgenetic alopecia just ended. Per the summary, SM produced a dose-dependent increase in mean terminal hair count of the frontal and vertex scalp and an improvement in hair density. There was no affect on blood pressure. In another article (link no longer active), reviewer Dr. Mirmirani says the following:
“The authors suggest that sublingual minoxidil (SM) may have better bioavailability and fewer hemodynamic effects by avoiding first-pass liver metabolism. Although the data in this study are positive, it will take more to convince me that it is significantly better than oral minoxidil (OM). Very few of my patients on low-dose OM for hair loss discontinue the medication due to side-effects. The other consideration is cost. OM it is an inexpensive, generic drug, that is covered by medical benefits.”
Update: January 2023 — I posted something on Twitter about sublingual minoxidil possibly being more effective than oral minoxidil. Below are the interesting responses from Dr. Corralo and Dr. Bhoyrul (affiliated with Sinclair Dermatology):
Sublingual vs Oral Minoxidil.Sublingual Minoxidil Sulfate.
Update: February 2023 — A HRN forum member named “Viney” is posting excellent details with photos of his hair regrowth from sublingual minoxidil and Dutasteride. He sees a dermatologist at Sinclair Dermatology (Melbourne, Australia).
