Lithium, polyuria and abnormal diurnal weight gain in psychosis

We evaluated diurnal weight gain and polyuria among 31 institutionalized chronically psychotic patients receiving lithium and 42 controls not receiving this drug. The patients were weighed weekly for three weeks at 7 a.m. and 4 p.m. We normalized the diurnal weight gain (NDWG) as a percentage by subtracting the 7 a.m. weight from the 4 p.m. weight, multiplying the difference by 100, and then dividing the result by the 7 a.m. weight. Polyuria was assessed using mean urine creatinine concentration (MUCR). NDWG was abnormal among study patients (1.9 +/- 1.2%) and controls (1.6 +/- 1.5%) independent of lithium treatment. The variation in MUCR explained about 20% of the variation in NDWG in both groups.