Intradermal Injection in Balding Areas versus Intramuscular Injection in Surrounding Muscles: A Split-Scalp, Randomized Controlled Trial Investigating Botulinum Toxin Injection Strategies for Androgenetic Alopecia Treatment

Recent advancements in androgenetic alopecia (AGA) treatment have highlighted the efficacy of botulinum toxin (BTX). However, inconsistencies in injection sites and depths warrant attention. While some studies have reported a preference for intradermal injections in areas of hair loss1,2, others have utilized intramuscular or subcutaneous injections in muscle regions surrounding the scalp such as the frontalis, temporalis, and occipitalis3,4. The support for the diversity of injection approaches is based on the current understanding that BTX can ameliorate AGA through two mechanisms: inhibiting transforming growth factor-β1 (TGF-β1) production by dermal papilla cells and relaxing surrounding muscles, which enhances scalp blood flow and oxygenation5. However, it remains unclear which injection strategy is more beneficial for patients. To address this issue, we registered and initiated a split-scalp, randomized controlled trial to compare the therapeutic effects of the two injection strategies.