act. The method is limited by excessive salivation washing the chemical down the throat. Also, many alkaloids have an unpleasant taste which makes them difficult to hold in the mouth. Tablets of psychoactive pharmaceuticals usually include bitter chemicals such as denatonium in order to discourage abuse and also to discourage children from eating them. Allergens Allergens may also be applied under the tongue as a part of allergen immunotherapy. Therapeutic peptides and proteins A relatively new way of administration of therapeutic peptides and proteins (such as cytokines, domain antibodies, Fab fragments or single chain antibodies) is sublingual administration. Peptides and proteins are not stable in the gastro-intestinal tract, mainly due to degradation by enzymes and pH differences. As a consequence, most peptides (such as insulin, exenatide, vasopressin, etc.) or proteins (such as interferon, EPO and interleukins) have to be administered by injection. Recently, new technologies have allowed sublingual administration of such molecules. Increased efforts are underway to deliver macromolecules (peptides, proteins and immunotherapies) by sublingual route, by companies such as Novo Nordisk, Sanofi and BioLingus. Sublingual delivery may be particularly effective for immuno-active medicines, due to the presence of immune-receptor cells close to the sublingual area. Vaccines The sublingual route may also be used for vaccines against various infectious diseases. Thus, preclinical studies have found that sublingual vaccines can be highly immunogenic and may protect against influenza virus and Helicobacter pylori, but sublingual administration may also be used for vaccines against other infectious diseases. Footnotes External links Routes of administration