Minoxidil (Rogaine) was approved for men by the US Food and Drug Administration (FDA) as a 2 percent topical solution in 1988 and as a 5 percent solution in 1997. The 2 percent solution was approved for women only in 1991. The 5 percent solution has not yet been approved for women, but it has been used worldwide by many dermatologists for many years.
Today, for the treatment of female pattern hair loss, the use of 2 percent topical Minoxidil is indicated in women older than 18 years with Ludwig stage I or II (mild to moderate) hair loss. The increase in hair counts following treatment with Minoxidil lotion is noticeable within 8 weeks and peaks after 16 weeks. The mechanism by which Minoxidil stimulates hair growth is still unknown – It is unlikely that the rapid increase in terminal hair counts is caused by reversal of follicular miniaturization. It is probable that Minoxidil triggers follicles in a latent phase of the hair cycle into anagen.
Clinical trials of Minoxidil for the treatment of female pattern hair loss
2% percent topical Minoxidil is the only currently FDA-approved agent for female pattern hair loss, having shown efficacy over placebo in many trials.
- In a well-designed 32-week study, investigator global assessment determined that the application of 2% Minoxidil twice-daily stimulated mild to moderate re-growth in 63% of 157 women compared with 39% of 151 women treated with vehicle.
- In a 32-week trial of 256 women aged 15 to 45 years with Ludwig I or II alopecia, non-vellus hair counts on the top of the scalp showed a mean increase of 14 percent over baseline for those on 2% topical Minoxidil as compared with 7.3 percent for those on placebo.
- Similarly, a 32-week, double-blind, placebo-controlled trial was conducted in 10 European centers to assess the efficacy and safety of 2% topical Minoxidil solution for the treatment of androgenetic alopecia in women. The results showed that in the 2% Minoxidil group, the mean increase in non-vellus hair count was 33 hairs, which was significantly greater than that of 19 hairs in the placebo group. New growth was seen by investigators in 44 percent of those treated with topical Minoxidil vs. 29 percent of those on placebo, leading to the conclusion that topical Minoxidil solution was significantly more effective than placebo in the treatment of androgenetic alopecia in women.
The outcome may not be as positive in those individuals with underlying hyperandrogenism. The increase in effectiveness of the 5% solution was not evident for women in FDA-controlled studies. In a 48-week, well-designed study on the comparative efficacy of 5% versus 2% topical Minoxidil in the treatment of mild to moderate female pattern hair loss, no significant difference in scalp coverage could be appreciated by investigator global assessment. However, patient satisfaction was appreciably greater with use of the higher concentration. Subsequent studies have shown at best a modest benefit from using the higher concentration in women, and its use should only be considered in those who show minimal response to the 2% formulation.
In the evaluation of female pattern hair loss using hair counts as a primary endpoint, studies have shown a mean increase in hair growth of 15–33% in the Minoxidil-treated groups compared with 9–14% in the vehicle control groups. One small study using hair weight as the endpoint found an increase of 42.5% in hair weights in the Minoxidil group compared to 1.9% in the controls. In the investigator and subject assessments, Minoxidil was superior to the vehicle but about 40% of subjects appeared not to respond to Minoxidil. None of these trials were extended beyond 32 weeks and the long-term results of Minoxidil treatment are uncertain. In men the beneficial effects on hair growth are lost rapidly on cessation of treatment and it is most likely that the same holds true in the case of women as well.
Clinical use in female pattern hair loss
One milliliter (25 drops) of Minoxidil solution must be used twice daily, in order to be effective. The drops must be applied directly onto a dry scalp and then slightly spread with the fingers. No more than 2 ml should be applied every day, regardless of the extent of the affected area. The best way for application is to make 5 partings in the hair and to put 5 drops in each part.
Side effects of Minoxidil treatment in female pattern hair loss
Minoxidil is poorly absorbed after topical application on normal intact skin, and only 0.3 to 4.5% reaches the systemic circulation. The percentage of Minoxidil that is absorbed is eliminated within 4 days. The effects on absorption of concomitant occlusion and the systemic metabolic biotransformation of topically applied Minoxidil are mostly unknown.
The most common Minoxidil side effects are simple contact dermatitis (scalp irritation, dryness, itching, scaling, and redness). 3 to 5% of women of women using Minoxidil develop hypertrichosis, a side effect of Minoxidil that is usually not perceived as a problem in men.
It is not clear yet why the hypertrichosis occurs but it is possibly through either a systemic effect or via a transfer of the drug, there is unwanted growth of hair affecting mostly the forehead, malar areas, and sides of the face. Hypertrichosis may diminish with continued treatment over the course of a year, and resolves completely within a few months once treatment is stopped. Pre-existing facial hair, higher dosing, and age older than 50 years are predisposing factors for hypertrichosis. Care also should be taken to avoid manual or fomites (e.g., pillows) spread of Minoxidil to sites other than the scalp, although the effect is largely believed to result from local absorption.
Studies have never shown any change in blood pressure or any other systemic effect, but Minoxidil solution should be used with caution in patients with cardiovascular disease.
Minoxidil should not be used in pregnant or nursing women. There is no evidence of teratogenicity in rats and rabbits, but Minoxidil has been found to be secreted in breast milk.