Doctors prescribe 40 milligrams of famotidine to treat stomach ulcers, gastroesophageal reflux disease and erosive esophagitis, notes Mayo Clinic. Failure to take this medication as directed by a doctor increases the chances of experiencing side effects.
An adult patient takes 20 milligrams of famotidine twice a day or 40 milligrams of famotidine once a day to treat symptoms of GERD and stomach ulcers. Dosages for children and teenagers are based on weight, states Mayo Clinic. A patient who has missed a dose should take it as soon as possible, or wait until it is time for the next dose. Potential side effects, though rare, include cough, itching and shortness of breath, and anyone having these symptoms should seek medical attention.