The international prevalence of legal high drugs necessitates the development of a method for their detection and identification. Herein, we describe the development and validation of a tetraplex multiplex real-time polymerase chain reaction (PCR) assay used to simultaneously identify morning glory, jimson weed, Hawaiian woodrose, and marijuana detected by high-resolution melt using LCGreen Plus((R)). The PCR assay was evaluated based on the following: (i) specificity and selectivityprimers were tested on DNA extracted from 30 species and simulated forensic samples, (ii) sensitivityserial dilutions of the target DNA were prepared, and (iii) reproducibility and reliabilitysample replicates were tested and remelted on different days. The assay is ideal for cases in which inexpensive assays are needed to quickly detect and identify trace biological material present on drug paraphernalia that is too compromised for botanical microscopic identification and for which analysts are unfamiliar with the morphology of the emerging legal high species.