You should contact your doctor for clarification. Zantac (ranitidine) belongs to a group of drugs called histamine-2 blockers. Ranitidine works by reducing the amount of acid your stomach produces. You may take up to two (2) Maximum Strength Zantac 150 ® tablets a day. Stop use and ask a doctor if you need to take this product for more than 14 days. Stop use and ask a doctor if you need to take this product for more than 14 days. Take Zantac (ranitidine) exactly as prescribed by your physician. Zantac (ranitidine) can be taken 150mg once to twice a day or 300mg once day. Antacids (e.g., Rolaids, Tums, or Maalox) can be. Can I take 600 mg of Zantac in one day? Some websites say 300mg is the maximum and a few say you can take up to 600mg. I took 400 mg about 9 hours ago. How should you take ZANTAC 150® Maximum Strength tablets? For relief of symptoms: Adults and children 16 years and older: Take one tablet swallowed whole with a glass of water when symptoms appear, day or night. how often can you take zantac? My doctor said to take it when you needed it. I usually take one or two pepcid ac's and a zantac 150.sometimes just 2 zantac 150s. While I don't believe this will harm you, you might want to discuss this health problem with your doctor and try a medication that is stronger so you wouldn't have to take 4 times a day. There are medicines that can be taken once a day that will control this problem. Just a thought. You may take up to two (2) Zantac 75 ® tablets a day. Stop use and ask a doctor if you need to take this product for more than 14 days. Stop use and ask a doctor if you need to take this product for more than 14 days. The Zantac dosage healthcare providers often recommend for treating adults with certain types of ulcers, GERD, or pathological hypersecretory conditions is 150 mg twice a day. Zantac is a medication that is available over the counter and by prescription in stronger formulations. It is primarily used to relieve the symptoms of heartburn as they relate to the production of stomach acid.