The active ingredient in it is prostaglandin, which is a part of prescription meds for glaucoma. One of its side effects is longer lashes, which this stuff kind of capitalizes on. But that also means that over time the "side" effects of this cosmetic stuff are often the same effect of glaucoma meds - darkening of the iris, changes in the pressure in your eyes, etc. I didn't think it was worth experimenting with when I read that.