 The postganglionic fibers reach the sublingual gland, and release acetylcholine and substance P. Acetylcholine, the primary neurotransmitter and the muscarinic receptors work to increase salivation.Many drugs are absorbed through sublingual administration, including cardiovascular drugs, steroids, barbiturates, benzodiazepines, opioid analgesics, THC, CBD, enzymes and increasingly, vitamins and minerals.When a chemical comes in contact with the mucous membrane beneath the tongue, it is absorbed.