Encyclopedia · growth stimulant
Setipiprant
An oral blocker of the PGD2 receptor GPR44 that was tested for male pattern baldness on strong lab data and grew no more hair than placebo in 169 men.
What it is
Setipiprant was developed for asthma and allergic rhinitis. It was never approved for any condition. Allergan ran a phase 2 trial in men with pattern hair loss.
How it works
PGD2 is raised in bald scalp and blocks follicle growth through the GPR44 receptor (not the other PGD2 receptor), which made GPR44 an attractive target (Garza 2012).
What the studies show
- In a placebo-controlled trial of 169 men over 24 weeks, 1000 mg twice daily changed target-area hair count by 7.1 versus 6.7 on placebo (difference 0.4, 95% CI -8.4 to 9.2, P=0.92). Self-assessment was also no different (trial record).
- Results sit on the trial registry; we found no peer-reviewed paper. The trial was industry-sponsored.
How it's used in studies
- 1000 mg twice daily for 24 weeks (trial record).
Side effects and safety
- Tolerability was acceptable in healthy volunteers and allergy trials.
Bottom line
Not available and not worth chasing: the cleanest human test of the PGD2/GPR44 idea was negative. It weakens, without disproving, the case that topical cetirizine works through PGD2. A topical GPR44 blocker has not been tested. Discuss with a doctor.
Fun facts
- A mechanism that looked convincing in tissue and mice produced essentially zero effect in a 169-man trial, a clean reminder that animal and tissue data alone are weak evidence.
Studies 2
ClinicalTrials.gov NCT02781311. A safety and efficacy study of setipiprant tablets in androgenetic alopecia in males. Allergan
Tested: setipiprant 1000 mg twice daily vs placebo
Result: Target-area hair count changed by 7.1 vs 6.7 on placebo (difference 0.4, P=0.92); self-assessment was also no different.
Read the study ↗Garza LA et al. Prostaglandin D2 inhibits hair growth and is elevated in bald scalp of men with androgenetic alopecia. Sci Transl Med. 2012
Tested: PGD2 measurement and exposure
Result: PGD2 was higher in bald scalp and inhibited hair growth in cultured follicles and mice through the GPR44 receptor.
Read the study ↗Related
- Topical cetirizineThe common allergy antihistamine, made up as a 1% scalp solution, has several small trials suggesting a modest effect that is weaker than minoxidil.
- LatanoprostA cheap glaucoma eye drop that lengthens and darkens eyelashes, with only a small pilot trial behind its off-label use on the scalp.
- BimatoprostA prostaglandin-like eye medicine that grows longer, thicker, darker eyelashes (and helps eyebrows), but did not work on the scalp.
- Prostaglandins and hairProstaglandins are fat-derived signals that switch follicles on or off; eye drops that copy one of them grow eyelashes but have not worked on the scalp.
- Hair growth pipeline (2026)What is in clinical trials for hair loss as of October 2026, how far along it is, and how much to trust the early numbers.