The active ingredient in the glaucoma medication Lumigan that was found to also stimulate lash growth. It has been approved by the FDA for use in Latisse, a prescription-only product manufactured and marketed by Allergan. Exactly how bimatoprost works to grow lashes isn't clear, but it may act by restructuring the phases of lash growth. Lashes in the telogen (resting) phase are prompted to return to the anagen (growth) phase, meaning you'll see newer, healthier lashes sooner. Bimatoprost is also believed to extend the growth phase of eyelashes, which is likely what takes once-puny lashes to longer, fuller lashes (Sources: Journal of Cosmetic Dermatology
, June 2010, pages 96-102; Clinical Ophthalmology
, April 2010, pages 349-358; and Drugs in Aging
, Volume 26, 2009, pages 1,049-1,071).
As with any drug, there are side effects to consider. The most commonly reported side effects from topical application of bimatoprost are stinging, redness, itching, and a burning sensation. These subside once use is discontinued. Other more serious side effects to be aware of include a permanent discoloration of the iris, more visible capillaries in the eye (which would make the whites of your eyes look redder), and a brownish discoloration along the lash line, where lash growth products containing bimatoprost are applied. In most cases, this discoloration is not permanent and will go away when you stop using the product with bimatoprost.