Pyridostigmine bromide is a drug used in the treatment of myasthenia gravis. Specifically, the drug is used to lessen muscle weakness in patients with this condition. Pyridostigmine bromide works by inhibiting an enzyme (called acetylcholinesterase) in synapses, which means acetylcholine is more readily available for synaptic use. Common side effects include upset stomach, diarrhoea, and vomiting.Pyridostigmine Bromide (Mestinon/ Regonol) is a cholinesterase inhibitor which works by improving nerve impulses in muscles making them work better. Pyridostigmine Bromide affects the body chemicals responsible for communication between nerve impulses and muscle movement. Pyridostigmine Bromide is mainly used to treat the symptoms of myasthenia gravis. However, this medication is also used to treat patients especially in the military who have been exposed to nerve gas. Pyridostigmine Bromide may also be used for other purposes as determined by the doctor. Do not use this medication if you are allergic to any ingredient in it or have a stomach or urinary blockage. Pyridostigmine Bromide may cause several side effects such as diarrhea, nausea, abdominal pain, increased urination, and dysmenorrhea. Consult the doctor if these side effects occur to you.