Cholinergic drug, any of various drugs that inhibit, enhance, or mimic the action of the neurotransmitter acetylcholine, the primary transmitter of nerve impulses within the parasympathetic nervous system—i.e., that part of the autonomic nervous system that contracts smooth muscles, dilates blood vessels, increases bodily secretions, and slows the heart rate. Cholinergic includes bethanechol, neostigmine, and pyridostigmine. Action, uses, dosages and side effects of all these drugs are also covered in this chapter. Serious side effects are seizures and bronchospasm. Common side effects are abdominal cramps, diarrhea, excess salivation, sweating, nausea, and vomiting.