Cimetidine is an H2-receptor antagonist indicated for the sho-term and maintenance treatment of duodenal and gastric ulceration, as well as gastroesophageal reflux disease. One of the primary disadvantages of using this agent, with respect to other H2-receptor antagonists famotidine and ranitidine, is that it is a relatively potent hepatic enzyme inhibitor. Therefore, this medication is likely to decrease the metabolism of other hepatically metabolized medications, such as phenobarbital. When the metabolism of a medication is decreased, the blood levels will increase, leading to an extension of the therapeutic effect and/or toxicity. Phenobarbital is a barbiturate indicated for the treatment of tonic-clonic seizures and status epilepticus. When the blood concentration of this medication increases, lethargy and feelings of intoxication may occur. Lansoprazole is a gastric acid proton-pump inhibitor indicated for the sho-term and maintenance treatment of duodenal and gastric ulceration, as well as gastroesophageal reflux disease. This agent does not affect hepatic enzymes. Ref: McQuaid K.R. (2012). Chapter 62. Drugs Used in the Treatment of Gastrointestinal Diseases. In B.G. Katzung, S.B. Masters, A.J. Trevor (Eds),Basic & Clinical Pharmacology, 12e.