True. Weight gain is a common side effect and an important health issue in patients on chronic antipsychotic therapy. Antipsychotics typically have some Anti-HAM properties (Histaminic, Adrenergic, Muscarinic) and the effects depend on the antipsychotic. The weight gain has been historically attributed to the antihistaminic effects. However, more recently experts have suggested that the weight gain is still not well understood. Anti-muscarinic references the blocking of muscarinic receptors in the cholinergic nervous system, resulting in increased heart rate, urinary retention, dry mouth, constipation, and other effects. Anti-adrenergic effects include orthostatic hypotension, sexual dysfunction, and changes in cardiac tissue electrical conduction.

Publication reference : Allison DB et al. Antipsychotic-induced weight gain: a comprehensive research synthesis. Am J Psychiatry. 1999 Nov;156(11):1686-96. Review. PubMed PMID: 10553730.
Reference URL: http://ajp.psychiatryonline.org/doi/abs/10.1176/ajp.156.11.1686?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub%3Dpubmed