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Retinoic Acid

Rob (PHH)

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Retinoic acid – or all-trans-retinoic acid or tretinoin - is a metabolite of vitamin A that the body needs in small amounts to function and stay healthy. 

Key insights:

  • The in vitro evidence suggests that retinoic acid can increase levels of sulfotransferase which may increase minoxidil efficacy (as minoxidil exerts its effect through its activation by sulfotransferase).
  • The ex vivo (in isolated cultured human hair follicles) evidence suggests that retinoic acid significantly inhibits hair follicle growth as well as induces the premature exit out of the growing stage (anagen) into the transitional stage (catagen) of the hair follicle cycle. Furthermore, an increase in a protein known to induce catagen, TGF-beta 2 was observed. In hair follicles isolated from patients treated with topical retinoic acid for 5 days, it was found that whilst sulfotransferase enzyme levels did not increase by any notable amount, the activity did significantly increase, which may subsequently increase the effectiveness of minoxidil.
  • The in vivo evidence suggests that the combination treatment of retinoic acid and minoxidil, while significantly enhancing hair growth, was not as effective as minoxidil alone, suggesting that retinoic acid may not actually increase minoxidil efficacy – like previously thought with in vitro studies.
  • Clinical research has typically determined the effect of retinoic acid in combination with minoxidil rather than alone. Some studies have found that while combination treatment with minoxidil does improve hair growth in patients with androgenetic alopecia, the effects have not been more beneficial than minoxidil alone.
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