The sleeping aide zolpidem works by making patients feel sleepy, which is an example of a. A physician writes a prescription for two painkillers that work together more effectively than either painkiller alone. The two drugs haveeffect. Both narcotic drugs and antihistamines cause drowsiness. When taken together, this is. The drug information for an antidepressant warns that in rare cases, patients may experience fast, uneven heartbeats or trouble breathing. This is an example of.