The most commonly implicated neurotransmitter in the aetiology of schizophrenia is

Schizophrenia is presently thought to be probably due to a functional increase of dopamine at the postsynaptic receptor, though other neurotransmitters such as serotonin (especially 5-HT2 receptors), GABA and acetylcholine are also presumably involved. Ref: A Sho Textbook of Psychiatry, Niraj Ahuja, 7th Edition, pg. no. 63