Learn about the potential side effects of Zantac (ranitidine). Includes common and rare side effects information for consumers and healthcare professionals. Selected from data included with permission and copyrighted by First Databank, Inc. This copyrighted material has been downloaded from a licensed data provider and is not for distribution, except. Doctors give trusted answers on uses, effects, side-effects, and cautions: Dr. Fowler on side effects of zantac 300 mg: I agree with dr elliott, and only wish to add that it is important not to use if there is a chance you could get pregnant, or are early in your pregnancy, since it can cause birth defects. Common and Rare Side Effects Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention. SIDE EFFECTS. Transient pain at the site of IM injection has been reported. Transient local burning or itching has been reported with IV administration of ZANTAC. Common Side Effects of Zantac. You should tell your doctor if any of the following side effects are severe or don't go away: Constipation, diarrhea, nausea, vomiting, or stomach pain The following side effects aren’t common and may happen in more than 1 in 1,000 people. Talk to your doctor or pharmacist if these side effects bother you or don’t go away: Talk to your doctor or pharmacist if these side effects bother you or don’t go away: How to use Zantac Tablet. Take this medication by mouth with or without food as directed by your doctor, usually once or twice daily. It may be prescribed 4 times a day for some conditions. Zantac (ranitidine hydrochloride) is a H2 (histamine-2) receptor blocker used for treating and preventing ulcers in the duodenum and stomach. Zantac is also used for treating Zantac eases and prevents heartburn associated with acid indigestion and sour stomach caused by eating or drinking certain foods and beverages.