Common side effects include nausea, increased saliva, crampy abdominal pain, and slow heart rate.[1] More severe side effects include low blood pressure, weakness, and allergic reactions.[1] It is unclear if use in pregnancy is safe for the baby.[1] Neostigmine is in the cholinergic family of medications.[1] It works by blocking the action of acetylcholinesterase and therefore increases the levels of acetylcholine.[1]