Sublingual (abbreviated SL), from the Latin for "under the tongue", refers to the pharmacological route of administration by which substances diffuse into the blood through tissues under the tongue.
Many drugs are absorbed through sublingual administration, including cardiovascular drugs, steroids, barbiturates, benzodiazepines, opioid analgesics, THC, CBD, some proteins and increasingly, vitamins and minerals.
When a chemical comes in contact with the mucous membrane beneath the tongue, it is absorbed. Because the connective tissue beneath the epithelium contains a profusion of capillaries, the substance then diffuses into them and enters the venous circulation. In contrast, substances absorbed in the intestines are subject to first-pass metabolism in the liver before entering the general circulation.
Sublingual administration has certain advantages over oral administration. Being more direct, it is often faster onset of action, and it ensures that the substance will risk degradation only by salivary enzymes before entering the bloodstream, whereas orally administered drugs must survive passage through the hostile environment of the gastrointestinal tract, which risks degrading them, by either stomach acid or bile, or by enzymes such as monoamine oxidase (MAO). Furthermore, after absorption from the gastrointestinal tract, such drugs must pass to the liver, where they may be extensively altered; this is known as the first pass effect of drug metabolism. Due to the digestive activity of the stomach and intestines, the oral route is unsuitable for certain substances, such as salvinorin A.
Pharmaceutical preparations for sublingual administration are manufactured in the form of:
Sublingual tablets—tablets which easily melt in the mouth, dissolve rapidly and with little or no residue. Nitroglycerine tablets are an example, the anti-emetic ondansetron is another.
Sublingual strips—similar to tablets in that they easily melt in the mouth and dissolve rapidly. Suboxone is an example of medication that comes in a sublingual strip.