Topical Minoxidil: Restarting After Acute Illness

What the over-the-counter product covers

Minoxidil 5% solution is over the counter, not prescription. The 2% solution's switch to over-the-counter status was approved on February 9, 1996 [2]. The men's 5% solution and women's 5% foam have separate topical product labels [1][3]. The men's 5% solution label covers the top of the scalp only, is for men only, and says it is not intended for frontal baldness or a receding hairline [1]. Directions are 1 mL with the dropper twice a day; more or more often will not improve results [1]. The women's 5% foam is half a capful once daily [3].

When the scalp is irritated or infected

The topical label lists scalp conditions that rule out use [1]. Its do-not-use list includes a scalp that is red, inflamed, infected, irritated or painful, and use of other medicines on the scalp [1]. The product is labeled for external use only, is not to be applied to other parts of the body, and eye contact is to be rinsed with cool tap water [1]. Scalp irritation or redness appears on the label's stop-use list [1]. The women's foam label calls the product extremely flammable and says to avoid fire, flame or smoking during and immediately after application [3].

If the illness involved the heart

Both labels list heart disease as a pre-use warning [1][3]. The stop-use list covers chest pain, rapid heartbeat, faintness or dizziness, sudden unexplained weight gain, and swelling of the hands or feet [1]. Those are the labeled cardiovascular and fluid checks for the topical product. Minoxidil tablets are a different, prescription medicine approved only for hypertension that is not manageable with maximum doses of a diuretic plus two other antihypertensive drugs [4]; the topical products are their own over-the-counter approvals [2].

What the 48-week trials measured

The two large trials behind 5% topical use started treatment rather than restarting it. In men, 393 volunteers aged 18 to 49 applied 5% solution (n=157), 2% solution (n=158) or placebo (n=78) twice daily for 48 weeks; 5% was superior to both 2% and placebo on change in nonvellus hair count [5]. In women, 381 volunteers aged 18 to 49 applied 5% (n=153), 2% (n=154) or placebo (n=74) twice daily; 5% was superior to placebo on all three primary measures at week 48 [6]. Both compared continuous use. The labels set expectations for that continuous use: results may occur at 2 months, and some men need at least 4 months [1]; the women's foam says 3 months, up to 6 months for some women [3].

What is not established

Nothing in these labels or trials answers how long to wait after a fever, whether a one- or two-week gap costs regrowth, or whether resuming leads to shedding. A review of minoxidil's action on hair describes shortened telogen in animal studies, probably similar in humans [7], but that work does not address restarting after a break.