Lansoprazole is a prescription medication which is available only under the brand name Prevacid. This medication belongs to a class of drugs known as proton pump inhibitors, or PPIs. When the body begins to digest food, acid is released in the stomach via a device known as a proton pump. The right amount of acid is necessary to enable food to digest properly, but too much causes heartburn. Prevacid blocks the pump from releasing excess acid, thereby preventing this painful consequence. Prevacid is used in the treatment of severe acid reflux, known as gastroesophageal reflux disease, or GERD and is also prescribed for stomach ulcers. Prevacid is available in 15 and 30 milligram capsules as well as dissolvable tablets. A powder that is mixed into water and taken orally is also available. This medication should generally be taken once a day. Swallow the capsule with water, or dissolve the tablet on your tongue. If you are taking the powder version of Prevacid, mix it with two tablespoons of water and drink immediately. The most commonly reported side effects of Prevacid include diarrhea, nausea, and stomach pain, but please ask your doctor for a complete list. Also, tell your doctor IMMEDIATELY if you experience an abnormal heartbeat or any other significant changes. Prevacid should be used cautiously by people taking Lanoxin for congestive heart failure, and may decrease the absorption of other medications. Ask your doctor for a full list of medications and conditions that should not be combined with Prevacid. Prevacid is frequently prescribed to treat stomach ulcers or GERD. However, this medication must always be used under the direct care of a physician. Please ask for and review all of the patient information provided by your doctor before taking Prevacid.