Objective: An effective way to protect the currently endangered wild populations of Lophophora williamsii is to select mescaline-rich specimens for selective propagation. Also, users of these and other entheogenic cacti are in need of an accessible way of dosing extracts. This research aims to introduce and validate an accessible procedure for the quantification of mescaline in fresh cactus tissue and aqueous cactus extracts, providing harm-reduction to entheogenic cactus populations and their users. Method: Standardized biopsy and Microscale Extraction followed by Scanometric Quantitative thin-layer chromatography (MESQ) were applied to live specimens and the extracts of Lophophora williamsii, Echinopsis lageniformis, E. peruviana and E.pachanoi. Results: The procedure was found to be valid for the intended applications. A previously undescribed radial mescaline gradient in L. williamsii and a longitudinal mescaline gradient in the Echinopsis species was thereby discovered. In the process, there also appeared to be a predictable correlation between the mescaline concentration in targeted biopsies and the strength of the overall cactus. Conclusion: This accessible and minimally invasive procedure is valid for the quantification of mescaline in live cacti and aqueous cactus extracts for breeding and dosing purposes. In addition, the MESQ-procedure holds promise as a valuable research tool for further botanical and phytochemical research.