BACKGROUND: Recently reported clinical data provides evidence that increasing the dose of botulinum toxin A increases the duration of efficacy. A 2-stage Phase 2, randomized, double-blind study investigated the duration of effect and safety of IncobotulinumtoxinA (INCO; Xeomin®, Bocouture®; Merz Pharmaceuticals GmbH, Frankfurt am Main, Germany) at doses higher than the approved 20 units (U) for glabellar frown lines (GFL). Primary safety and efficacy endpoints of Stage 1 are reported here. METHODS: 151 subjects with moderate-to-severe GFL were randomized 1:2:2 to receive a single treatment with 20U, 50U, or 75U INCO. The primary efficacy endpoint was median duration of at least 1-point improvement from baseline as assessed by investigator at maximum frown on the Facial Wrinkle Scale. RESULTS: The median duration of effect was 185 days for the 50U dose group (95% CI:[182, 205]) and 210 days for the 75U dose group (95% CI:[182, 217]). Duration of effect was significantly longer for 75U vs 50U (P=0.0400) and 20U (P=0.0166) despite the study not being powered for confirmatory statistical significance testing between the dose groups. Duration of effect was also longer for 50U vs 20U, however; statistical significance was not reached (P=0.4349). The incidence of treatment-related adverse events was low across all doses (20U:2[6.7%], 50U:6[10.0%] and 75U:8[13.1%]). CONCLUSIONS: These results demonstrate a dose effect of at least 6 months duration with higher doses in the majority of GFL subjects. All doses were well tolerated and safety was consistent with the known safety profile of 20U INCO for GFL. J Drugs Dermatol. 2020;19(10):985-991. doi:10.36849/JDD.2020.5454.