Leptin seems to regulate various physiological mechanisms besides body weight. Leptin plays a role in vascular biology and pathology as well as renal function. In addition, leptin has been implicated in the regulation of fertility and reproduction. The effect of pharmaceutical agents on circulating plasma leptin levels has been assessed. Among the drugs investigated are glitazones, statins, fibrates, serotonin reuptake inhibitors and cannabinoid-1 receptor antagonists. Since these agents are used to treat pathological conditions there is a potential role for leptin in these states. The degree of involvement of leptin in several pathophysiological states needs to be defined to aid in the development of potentially useful therapeutic agents.