Last month we talked about circadian rhythms and how our skin cells show a circadian rhythmicity which regulates cell proliferation, DNA repair and pigmentation amongst others.
It therefore shouldn’t be surprising that our hair growth is also under a circadian rhythm and this month’s edition of the British Journal of Dermatology contains an article discussing this.
[Maas, D, Spindler A, Zappi I et al. Increased efficacy of daytime low-dose oral minoxidil dosing for androgenetic alopecia: a retrospective study. Br J Dermatol 2026;195:689-691.]
What does the paper say?
The paper is actually discussing at whether the timing of administration of low-dose oral minoxidil for a hair loss condition called androgenetic alopecia could cause a greater improvement in hair density.
What is minoxidil?
This is a medication that has been around for some time, since the 1960’s. It was originally used to treat high blood pressure but then was found to cause hair growth. It was then repurposed for the treatment of hair loss and has been available over-the-counter in a topical form for hair loss since the 1980s to 1990s. You may have seen it in chemists as Regaine® in the UK (it has other names in other countries).
It is also available in tablet form on prescription and dermatologists prescribe this off-licence in low doses to treat the hair loss condition androgenetic alopecia in both men and women.
[Akiska YM, Mirmirani P, Roseborough I et al. Low-dose oral minoxidil initiation for patients with hair loss. An International Modified Delphi Consensus Statement. JAMA Dermatol 2024;161:87-95.]
[Gupta AK, Talukder M, Williams G et al. Low-dose oral minoxidil (LDOM) and topical minoxidil: consensus recommendations for managing male and female pattern hair loss in hair transplant patients using a modified delphi process. Expert Opinion on Pharmacotherapy 2026;27:253-261.]
How does minoxidil work?
It’s still not fully understood, despite it being around for at least 30 years. It is thought to act as a vasodilator, increasing blood flow to the hair follicle. It also has been suggested to cause hair follicles to shift to the growth phase or anagen phase and it has also been shown to stimulate prostaglandin E2 production which enables hair follicles to grow continuously. It might possibly work as an antiandrogen too.
[Suchonwanit P, Thammarucha S, Leerunyakul K. Minoxidil and its use in hair disorders: a review. Drug Des Devel Ther 2019;13:2777-2786.]
Does minoxidil work?
There are lots of studies showing its efficacy in stimulating hair growth in men and women. As a topical preparation, the 5% strength is more effective than the 2% strength.
What are the side effects?
Not surprisingly, you can get excess hair growth (which we call hypertrichosis) in other areas of the face and body. It can also cause cardiovascular side effects such as swelling or oedema or a fast heart rate in some. The topical version can also cause skin irritation. It also takes some time to work and if you stop it, all hairs grown on minoxidil will fall out.
When would you choose oral minoxidil?
Low-dose oral minoxidil (LDOM) would be an option if the topical preparation didn’t work or caused unacceptable side effects such as skin irritation. It cannot be used in anyone with a history of cardiac disease, low blood pressure, cardiac arrhythmias, kidney disease or were pregnant or breastfeeding.
So does the time of day that you take the tablet make a difference?
This particular study looked at 329 patients of which 68 took the tablet during the day and 261 took the tablet at night though the exact timings were not noted.
They found that those who took the tablet during the day had a greater improvement in hair density than those who took it at night.
Why did they think this was?
They thought it might reflect increased LDOM-induced blood flow and nutrient delivery to the proliferating keratinocytes whose peak activity is during the early daytime hours. A previous small study of 9 patients from 1969 confirms this.
[Comaish S. Autoradiographic studies of hair growth in various dermatoses: investigation of a possible circadian rhythm in human hair growth. Br J Dermatol 1969;81:283-8.]
In conclusion…
It’s food for thought, isn’t it? That now the time you take your medication can influence the result. More studies are needed, for sure!
Kind regards,
Sandy
Dr Sandy Flann, Consultant Dermatologist.
