Tums has the benefit of working almost immediately after taking, but unfortunately, the effects do not last long. In general, each dose of Tums lasts for 1 to 3 hours and often lasts even shorter periods of time if taken immediately after food.
The short duration of action of Tums is due to how the drug works. Tums contains calcium carbonate and when taken by mouth, it effectively neutralizes stomach acid and raises the pH (i.e. lowers the acidity) of gastric contents. This helps to reduce the symptoms as gastric reflux and heartburn.
Unfortunately, Tums does not alter or change how gastric acid is released, unlike many of the newer antacids on the market such as the PPI (Proton Pump Inhibitor) class of medcations. Once the calcium carbonate is used up, the pH in stomach will begin to lower (i.e. become more acidic) again. When food is present in the stomach, our bodies are programmed to produce acid, which is why Tums lasts for shorter periods of time after a meal.
Due to the short duration of action of Tums, it often needs to be dosed every 1 to 2 hours. This is not a problem if you have a short term problem but if you are having recurrent symptoms, a longer lasting product such as Prilosec or Pepcid may be a better option.