Ranitidine is a common over-the-counter medication that works by reducing the amount of acid produced by the stomach. It’s really helpful for conditions like heartburn and acid reflux, both of which are caused by an overabundance of stomach acid.[1] Ranitidine is a fairly safe medication, but like any over the counter drug it should be taken according to doctor or manufacturer directions. Always talk to your doctor before beginning any new medication regimen. Part 1 - Determining the Proper Dose by Condition 1 → Take 150 mg to manage a gastric or peptic ulcer. Ranitidine may be used to manage a duodenal ulcer, a type of peptic ulcer in the small intestine, as well as gastric ulcers. An adult may take 150 mg twice a day or 300 mg once a day to help manage symptoms. Additionally, you can take 150 mg once a day to help prevent symptoms. → For children under 16, it is recommended that you do not exceed 300 mg per day for treatment, and no more than 150 mg per day for symptom m...