Clozapine is a dopamine receptor antagonist that blocks a range of other monoamine receptors and may have some effects on the glutamatergic system. There is evidence that it has better efficacy and effectiveness than other dopamine antagonists in treating schizophrenia that has failed to respond to other dopamine receptor antagonists. It appears to reduce impulsive behaviours such as violence (Frogley et al., 2011), self-harm (Meltzer et al., 2003) and substance misuse (Lalanne et al., 2016) and to have mood-stabilizing properties (Chang et al., 2006). In the UK it is licensed for three indications: (i) treatment-resistant schizophrenia, (ii) for treating schizophrenia when other antipsychotics have led to severe neurological adverse reactions and (iii) treating psychosis associated with Parkinson’s disease where standard treatment has failed (electronic Medicines Compendium, 2019).