Latanoprost for Eyelash Growth: Evidence, Off-Label Use, and Risks

Latanoprost is a prostaglandin F2-alpha analog approved to lower pressure inside the eye. The FDA cleared it in 1996 under the brand name Xalatan for elevated intraocular pressure in open-angle glaucoma and ocular hypertension, and it was the first prostaglandin analog approved for that purpose. It works by increasing the outflow of fluid from the eye, which drops the pressure that can damage the optic nerve in glaucoma. It is a once-daily eye drop and is now a low-cost generic.

Growing eyelashes or eyebrows is not an approved use of latanoprost. The FDA has never reviewed or cleared it for that purpose, so lash use is off-label, decided between a person and a clinician rather than backed by an approval.

The approved lash drug is a different prostaglandin. Bimatoprost, sold as Latisse, was approved in December 2008 to treat inadequate or not enough eyelashes, a condition called hypotrichosis. Latisse is the same molecule as the glaucoma drop Lumigan, reformulated and labeled for cosmetic lash use. Calling latanoprost an approved lash treatment would be wrong; that description belongs to bimatoprost.

Prostaglandin analogs make lashes longer, thicker, and darker by acting on the hair follicle. Each hair cycles through a growth phase, called anagen, and a resting phase. Prostaglandins lengthen the growth phase and pull more follicles into it at once. The result is a hair that grows for longer before it sheds, plus more hairs growing at the same time, so the fringe of lashes looks fuller. The drugs also raise pigment in the hair, which darkens the lash.

This is the same biology behind the side effect in glaucoma patients. A drop meant for the eye coats the lash line and the skin at the base of the lashes, and the follicles there respond by growing longer darker hair. Latanoprost and bimatoprost share this class effect, which is why an eye-pressure drug ended up being studied for cosmetics.

The cosmetic use came straight out of a glaucoma side effect. When prostaglandin drops entered wide use in the 1990s, doctors and patients reported that lashes on the treated side grew longer, thicker, and darker, and the eyelid skin sometimes darkened too. These reports were noted as adverse effects, since they were unexpected and uneven between the two eyes.

A manufacturer turned that observation into a product. Bimatoprost, already sold as a glaucoma drop, was tested directly for eyelash growth and approved as Latisse in 2008. So the approved lash drug exists because someone followed up a glaucoma side effect that the whole prostaglandin class shares, latanoprost included.

The strongest trial evidence is for bimatoprost, not latanoprost. In the pivotal bimatoprost trial, 278 adults with inadequate lashes were randomized to once-daily bimatoprost 0.03% (137) or vehicle (141) for five months. By week 16, 78.1% of treated subjects showed at least a one-grade increase in eyelash prominence on the investigator scale, against 18.4% on vehicle, and the treated group had significantly greater gains in lash length, thickness, and darkness, all at P below .0001 (Smith 2012). This trial supports the Latisse approval.

The latanoprost-specific evidence is much smaller. A randomized double-blind placebo-controlled pilot enrolled 30 healthy volunteers, half on latanoprost 0.005% applied to the lash line and half on vehicle, for three months. The latanoprost group showed a significant increase in eyelash length and a darkening of color, while the placebo group stayed flat (Hassan 2023). It is a pilot of 30 people, not a large registration trial, so it points the same direction as the bimatoprost data without carrying the same weight.

Results are mixed where the follicle itself is damaged. A 16-week randomized study of latanoprost and bimatoprost in people who had lost eyelashes to alopecia areata found no meaningful regrowth (Roseborough 2009). The reasonable read is that prostaglandins can enhance lashes that are present but underwhelming, which is the cosmetic case, while a follicle shut down by autoimmune disease may not respond.

Most of what is known about latanoprost's risks comes from its use in the eye, and the most serious one is permanent. Latanoprost can increase brown pigment in the colored part of the eye, the iris, and after the drug is stopped that iris darkening is likely to be permanent (Xalatan prescribing information). The change is most associated with the drop going into the eye, and it matters most for people with mixed-color irises, where a brown tint can spread. Applying a prostaglandin at the lash line raises the chance some reaches the eye.

The skin and lash changes are usually milder and often reversible. Latanoprost can darken the skin around the eye, an effect that has been reported to reverse in some people after stopping. It changes the lashes themselves, increasing length, thickness, and number, which is the intended cosmetic effect. It can also cause red, irritated eyes, listed on the label as conjunctival hyperemia, and in the bimatoprost trial red eyes were the one adverse effect clearly more common than with vehicle (Smith 2012).

One more effect is worth naming. Prostaglandin glaucoma drops have been linked to loss of fat around the eye and a deepening of the eyelid crease, sometimes called a sunken look, and the latanoprost label lists deepening of the eyelid sulcus among reported effects (Xalatan prescribing information). This is mainly described with drops used in the eye over time. Putting a prostaglandin near the eye carries these risks, which is the core reason the choice belongs with a clinician.

Using latanoprost for lashes is a judgment call, not an approved treatment. It is off-label, the trial record behind it is a single small pilot, and bimatoprost (Latisse) is the prostaglandin the FDA actually reviewed and cleared for eyelashes. Someone weighing latanoprost is usually trading the larger evidence base and the on-label option for a cheaper generic that works through the same mechanism.

The risks are the same family for both drugs, and the iris-darkening risk is the one to take seriously because it does not reverse. A clinician can look at your eye color, your reason for wanting it, and your history, then decide whether a prostaglandin makes sense at all and which one. People who want the approved, better-studied path generally choose bimatoprost. The point is to make that call with a clinician rather than on your own. A closer look at the latanoprost lash story is in our explainer on latanoprost and eyelash growth.