Related

Tier	What is in it	Status	Does it work?
Prescription	Bimatoprost 0.03% (Latisse)	FDA-approved drug	Yes — approved for hypotrichosis of the eyelashes on trial evidence
Cosmetic serums containing prostaglandin analogues	Isopropyl cloprostenate, dechloro-dihydroxy-difluoro ethylcloprostenolamide, and similar	Unapproved new drugs in FDA's view	Yes — with the same side effects
Genuine cosmetic conditioners	Peptides, panthenol, biotin, castor oil, amino acids	Cosmetic	Conditioning and appearance at best; no reliable growth

Bimatoprost is a prostaglandin analogue developed for glaucoma. Longer, thicker, darker lashes turned up as a side effect in glaucoma patients, and the lash indication followed. The mechanism is an extension of the anagen (growth) phase of the lash cycle and an increase in the number of follicles in it.

It works, and the side effects come from the same mechanism:

• Permanent iris darkening — brown pigment increasing in blue, green or hazel irises. This is the one that does not reverse.
• Eyelid skin darkening, which usually does reverse on stopping.
• Periorbital fat atrophy — a hollowed, sunken look around the eye, reported with prostaglandin analogues and slow to recover.
• Redness, itching, dry eye.
• Loss of the gained lashes within weeks of stopping. It is a maintenance drug.

FDA has issued warning letters to companies marketing lash serums containing isopropyl cloprostenate and related prostaglandin analogues, on the basis that a product intended to affect the structure or function of the body is a drug under FD&C Act sec. 201(g) — and, having no approved application, is an unapproved new drug and also misbranded.

The consumer-facing summary: a cosmetic that genuinely grows lashes is, by definition, making a drug claim. If it works the way it says, it is not a cosmetic. If it is a cosmetic, it conditions.

Products have been reformulated and renamed repeatedly in response to enforcement, so the presence or absence of a prostaglandin analogue is best checked by reading the ingredient list for anything ending in -prost, -prostenate or -prostenolamide.

Condition the lash shaft so it looks glossier and breaks less; hydrate the lash line; and, with peptides, make an appearance claim that is difficult to disprove and difficult to demonstrate. Castor oil, the most common home remedy, has no controlled evidence for lash growth — and getting oil into the eye nightly is its own irritation.

What actually helps most lashes: stop over-curling, stop scrubbing off waterproof mascara, take breaks from extensions, and treat the underlying blepharitis if it is there. Lash loss can also be a medical sign — thyroid disease, alopecia areata, trichotillomania, chemotherapy — and is worth a clinician's opinion rather than a serum.

Cosmetic — FDA primary category (03) eye makeup preparations — only for genuine conditioners with appearance claims. Anything intended to grow lashes is a drug.

Under MoCRA the small-business exemption does not apply to eye-contact products, and serious adverse events must be reported to FDA within 15 business days — which is how iris and periorbital effects from cosmetic-marketed serums become visible.

In the EU, prostaglandin analogues intended to affect lash growth are similarly treated as falling outside the Cosmetics Regulation, and several have been the subject of national market withdrawals.

Six months after opening for a wand or brush applicator that returns to the tube after touching the lash line. Stop at the first sign of eye irritation, redness, darkening or discomfort and see a clinician — and in this category, do that promptly, because two of the possible effects do not fully reverse.

• Makeup — the shelf this sits on, and the rest of it.
• Cosmetics — what the label is legally allowed to say, and the full catalogue.
• The rest of Eyes — Eyeshadow · Eyeshadow Primer · Eyeliner · Kohl and Kajal · Mascara · Lash Primer · False Eyelashes · Eyelash Adhesive · Eye Makeup Remover · Eyelash Cleanser.
• Hair Growth Serum — the same drug/cosmetic argument on the scalp.
• The FDA Isn't That Great — the sceptical read on the agency policing this.
• Regulatory statements here follow the FDA and EU sources listed on Cosmetics, read 16 August 2026.