It is the general hope of all clinicians that patients will respond to a single therapeutic agent. However, such a response may be the exception rather than the rule. Although for a long time there was much warranted consternation regarding polypharmacy (patients receiving too many different types of medications), many patients do require simultaneous treatment with different classes of drugs to achieve an adequate response. There are a number of reasons for combining medications. Among the most common is to augment the effect of one agent—for example, lithium is combined with an antidepressant to enhance or bring about an antidepressant effect, or two mood stabilizers are combined to reduce breakthrough mania. A second common reason for adding one medication to another is to treat one aspect of the illness—for example, a hypnotic added to an antidepressant to help with sleep, or a stimulant is added to combat residual fatigue. Medications are also commonly combined to reduce side effects of particular agents—for example, antiparkinsonian drugs are added to standard antipsychotics.