Over-the-counter (OTC) products are medicines you can buy without a doctor’s prescription.

Antacids reduce the effect of (neutralize) the acid in your stomach. They can provide fast, short-term relief. Many OTC medicines combine different antacids.

H2 blockers reduce the amount of acid your stomach makes. While they don’t relieve symptoms right away, H2 blockers relieve symptoms for a longer period of time than antacids. They usually start to work within an hour. Examples of H2 blockers available over the counter are ranitidine (brand name: Zantac) or famotidine (brand name: Pepcid).

Proton pump inhibitors greatly reduce your body’s production of acid. They work well for heartburn that isn’t resolved by antacids or H2 blockers. It may take a little longer for a proton pump inhibitor to help your symptoms than an H2 blocker, but relief will last longer. These medicines are most helpful for people who have heartburn often — more than two days a week. Omeprazole (brand name: Prilosec) is an example of a proton pump inhibitor.

Despite the many brands, Antacids  all rely on various combinations of three basic ingredients: magnesium, calcium, or aluminum:

Magnesium. Magnesium salts are available in the form of magnesium carbonate, magnesium trisilicate, and most commonly, magnesium hydroxide (Milk of Magnesia). The major side effect of magnesium salts is diarrhea. Magnesium salts offered in combination products with aluminum (Mylanta and Maalox) balance the side effects of diarrhea and constipation.

Calcium. Calcium carbonate (Tums, Titralac, and Alka-2) is a potent and rapid acting antacid that can cause constipation. These antacids are actually sources of calcium. There have been rare cases of hypercalcemia (elevated levels of calcium in the blood) in people taking calcium carbonate for long periods of time. This can lead to kidney failure and is very dangerous. None of the other antacids has this side effect.

Aluminum. Aluminum salts (Amphogel, Alternagel) are also available. The most common side effect of antacids containing aluminum salts is constipation. People who take large amounts of antacids that contain aluminum may also be at risk for calcium loss, which can lead to osteoporosis.

H2 blockers impede acid production by blocking or antagonizing the actions of histamine, a chemical found in the body that encourages acid secretion in the stomach. They are available over the counter and provide symptom relief in about half of GERD patients. It takes between a half hour to 90 minutes for them to work, but benefits last for hours. The drugs are usually taken at bedtime. Some people may need to take them twice a day.

H2 blockers inhibit acid secretion for 6 to 24 hours and are very useful for people who need persistent acid suppression. They may also prevent heartburn episodes in people who are able to predict its occurrence. In some studies, H2 blockers improved asthmatic symptoms in people who suffer from both conditions. A 2001 study suggested, however, that they rarely provide complete symptoms relief for chronic heartburn and dyspepsia and they have done little to reduce office visits to physicians for GERD.

Four H2 blockers are currently available in the U.S.:

Antacids Side effects

Excess calcium from supplements, fortified food and high-calcium diets, can cause the milk-alkali syndrome, which has serious toxicity and can be fatal. In 1915, Bertram Sippy introduced the "Sippy regimen" of hourly ingestion of milk and cream, the gradual addition of eggs and cooked Marielle F BeRR..<3 cereal, for 10 days, combined with alkaline powders, which provided symptomatic relief for peptic ulcer disease. Over the next several decades, the Sippy regimen resulted in renal failure, alkalosis, and hypercalcaemia, mostly in men with peptic ulcer disease. These adverse effects were reversed when the regimen stopped, but it was fatal in some patients with protracted vomiting.

Milk alkali syndrome declined in men after effective treatments were developed for peptic ulcer disease. But during the past 15 years, it has been reported in women taking calcium supplements above the recommended range of 1200 to 1500 mg daily, for prevention and treatment of osteoporosis, and is exacerbated by dehydration. Calcium has been added to over-the-counter products, which contributes to inadvertent excessive intake. The New England Journal of Medicine reported a typical case of a woman who arrived in the emergency department vomiting and in altered mental status, writhing in pain. She had consumed large quantities of chewable antacid tablets containing calcium carbonate. She gradually recovered.