betahistine + olanzapine

Betahistine + olanzapine is a combination of two small molecule drugs, typically co-administered rather than formulated as a fixed-dose product. Olanzapine is an atypical antipsychotic primarily used for the treatment of schizophrenia and bipolar disorder; it acts mainly as an antagonist at dopamine D2 and serotonin 5-HT2A/2C receptors, but also has high affinity for histamine H1 receptors, which contributes to its side effects such as weight gain and somnolence. Betahistine is a centrally acting histamine H1 receptor agonist and H3 receptor antagonist, originally indicated for Ménière's disease. When combined with olanzapine, betahistine has been shown in both animal models and clinical studies to mitigate olanzapine-induced weight gain and reduce somnolence by counteracting the antagonism of histamine H1 receptors caused by olanzapine[1][2][4][6]. The combination does not appear to diminish the antipsychotic efficacy of olanzapine but may improve tolerability regarding metabolic side effects.