[jaijaihanuman]

Quetiapine is labaled an anti-psychotic yes, but its pharmacological characteristics are not that straight forward. It has a much higher affinity for H1 (histamine) receptors than for D2 (dopamine) receptors. Meaning that in low doses it acts like an anti-histaminergic drug, having a very limited effect on dopaminergic systems. Around 60% of D2-receptors need to be blocked for a typical anti-psychotic effect, and that is nowhere near what is happening with say 50mg of quetiapine, which is a normal dose for sleeping aid. In those low doses it mainly acts on H1, alpha-1, M3, M1, and some 5HT type receptors. At a minimum of 300mg per day, it pharmacologically starts to act as an anti psychotic.

There is a nice brief summary of this in Stahl's Essential Psychopharmacology.

To be clear, I am very much against prescribing anti-psychotics as sleeping aids. But I don't think there is a strong case for calling quetiapine anti-psychotic in low doses.