The Effect of Placebo in Split-Scalp and Whole-Head Platelet-Rich Plasma Trials for Androgenetic Alopecia Differs: Findings from a Systematic Review with Quantitative Evidence Syntheses

The study "The effect of placebo in split‐scalp and whole‐head platelet-rich plasma trials for androgenetic alopecia differs: Findings from a systematic review with quantitative evidence syntheses" found that the placebo effect significantly varies between split-scalp and whole-head trials on platelet-rich plasma (PRP) monotherapy for androgenetic alopecia (AGA). The researchers found that total hair density after 6 months was significantly higher in the placebo arm of split-scalp trials, compared to whole-head studies, by 37 hairs/cm2. The difference in total hair density between patients receiving PRP and those on placebo was -30 hairs/cm2 for whole-head studies, indicating a larger decrease in hair density. The study suggests that patients in the placebo group in whole-head trials lost significantly more hair than in the placebo side of the split-head trials, presumably because of PRP diffusing from the treatment side of the scalp. This "design effect" could partly reconcile the incongruent conclusions across the PRP literature for AGA.