Like all cholinergic drugs, Mestinon can have undesirable functional effects on the autonomic nervous system.
Muscarinic-type side effects can manifest themselves as nausea, vomiting, diarrhea, stomach cramps, increased peristalsis and bronchial secretion, salivation and lacrimation, as well as bradycardia and miosis. Nicotine-type side effects consist mainly of muscle spasms, muscle twitches and muscle weakness.
Like other bromine-containing drugs, Mestinon can occasionally cause skin rash, though this generally disappears rapidly after medication has been discontinued. Further use of Mestinon or other bromine-containing preparations is then contraindicated.