Edema is a clinical apparent increase in interstitial fluid. The interstitial fluid expansion can be generalized or localized. The prevalence depends on the specific etiology.

Two basic processes in the occurrence of edema are extravasation of fluid from capillaries to the interstitium and retention of sodium and water by the kidneys. Edema usually is clinically apparent after 2–3 L of fluid accumulation in the interstitium. The severity of edema depends on the underlying etiology.

See table for major causes of peripheral edema.

The most commonly accepted mechanism is capillary vasodilation from alpha-1 adrenergic blockade though water retention through activation of renin–aldosterone system is also postulated.

Among psychotropic agents, antipsychotics are most commonly associated with edema. The estimated prevalence is low at 1–3% [1]. The antipsychotics most commonly implicated are risperidone, olanzapine, and quetiapine [1]. Cases have been reported for chlorpromazine, haloperidol, paliperidone, clozapine also. The onset of edema is usually within 4 weeks of starting medication and occurs more commonly in females. In several patients, the medication had to be stopped due to severe or painful edema that interfered with functioning. All cases reported reversibility of edema with discontinuation of medication.