Plasma folate and affective morbidity during long-term lithium therapy.

In 107 patients on long-term lithium, those with lower plasma folate concentration had a higher affective morbidity than those with higher folate, both at the time and during the previous two years. The association was not the results of weight change or the concomitant use of other drugs. Animal work reporting a decreased synthesis of 5-HT both in folate-deficient animals and in animals fed excessive amounts of folate suggests that it may be important for lithium patients to receive folate supplements to their diet for maximum therapeutic effect.