A 2022 randomized comparative trial (Panahi et al.) found that 2% rosemary oil applied twice daily produced hair-count improvements comparable to 2% topical minoxidil after 6 months, with significantly less scalp itching reported in the rosemary group. HairReve Hair Rescue Thickening Serum uses rosemary extract as one of its core actives, alongside caffeine, green tea, zinc, and larch tree extract, and was separately tested in a DOH-Tondo Medical Center pilot study showing 15-18% hair density improvement over 16 weeks.