Saliva is an excellent analytical matrix for the detection of illicit drug residues such as tetrahydrocannabinol and amphetamine. Analysis of drugs in saliva offers significant advantages compared to blood or urine. These include ease of sample collection, reduced sample processing and greater accessibility for collection. However to fully exploit its potential knowledge of the physiology and of saliva, salivary drug metabolism, optimal collection strategies, rapid, sensitive and specific assays and possible interferences is required. The method selected for sample collection can also have a significant impact on the validity of the testing method. This review critically analyses these factors, the current approaches used and potential future developments in salivary drug analysis.