The term “Oral fluid” is used for collected salivary matrix for the reason that the actual sample is a mixture of fluids originating from 3 pairs of salivary glands (parotid, submandibular, and sublingual), also including several minor glands and oral mucosa. Even though water makes up the majority of the specimen, some bacteria and epithelial cells are also present. An approximate production of saliva of an healthy adult is 0.5-1.5 L of saliva per day (0.4 mlVmin); however, its contents and thickness can vary within an individual which also has a great effect for the time required to collect the required concentration of drug.
Certain diseases like diabetes and alcoholism alters the saliva production, which cause a reduction in salivary flow. In 2005, Aps and Martins published a detailed paper on drugs and disease conditions that may affect saliva production. They pointed out certain conditions that leads to decreased saliva flow namely as follows, menopausal hormone changes, stress, smoking, anti-cholinergic drugs that inhibit parasympathetic nerve impulses, analgesics, anticonvulsants, and tranquilizers. On the other hand, saliva production can be increased by external acidic stimulus (e.g., citric acid), pain, chewing, or ingestion of cholinergic drugs. Kato et al. studied the effect of stimulation on cocaine concentration. They reported momentous increases in cocaine levels in nonstimulated compared to stimulated saliva. O’Neal et al. showed similar responses following the administration of codeine. This is an important issue if collection devices are proposed to stimulate saliva flow to turn out an adequate sample so that false-negative results may not occur as a result of dilution of the specimen.