The use of cholecystokinin in schizophrenia: a review.

Cholecystokinin (CCK) is a peptide originally isolated from the gut. It has been investigated as a candidate treatment for schizophrenia on the assumption that the illness is associated with an imbalance between CCK and dopamine in the mesolimbic dopamine system. Many of the studies to assess the efficacy of CCK used open designs and are prone to observer bias and over-optimistic reporting. Most of the studies used CCK as an adjunct to standard neuroleptic treatment and are too small to be able to demonstrate extra efficacy above that of the active compound. Only three out of ten studies using CCK or placebo as an adjunct to neuroleptics reported limited efficacy. Of the 14 placebo-controlled reports only three were in drug-free patients. These were unfortunately too small, or too brief, to draw valid conclusions of efficacy. A summary of these data suggests that although 500 patients have received CCK, its efficacy in the treatment of schizophrenia has not been properly tested.