Over the past five years the number of internet sites advertising 'legal highs' has literally exploded, as have user reports of experiences (both pleasurable and frightening) with these substances and the number of emergency room visits by users. Although the majority of these 'legal highs' have been described as bath salts and herbal extracts, most contain neither plant derived compounds nor components of personal hygiene products. So-called 'bath salts' largely contain synthetic analogs of the natural compound Khat; spice-related materials, claimed to be 'legal marijuana,' are mostly synthetic analogs of cannabinoid receptor ligands that were developed as research tools. This review describes the emergence and properties of these two groups of 'legal highs' from a medicinal chemist's perspective
