Table 1. Association of catechol-O-methyltransferase genotype polymorphism with psychiatric disorders.

COMT: catechol-O-methyltransferase; IL-10: Interleukin-10; DRD2: dopamine receptor D2; DLPFC: dorsolateral prefrontal cortex; G allele: guanine allele; Met: Methionine; Val: Valine; SNP:  single nucleotide polymorphism; ANKK1-DRD2: Ankyrin Repeat and Kinase Domain Containing 1 - Dopamine Receptor D2 complex; ELA: early life adversity; METH: methamphetamine

Author	Year of publication	Type of study	No. of subjects	Purpose of study	Results /conclusion
Wang J et al. [15]	2021	Observational	640	To assess the effect of interaction between COMT and IL-10 genotype polymorphisms on cognition in chronic schizophrenics.	COMT genotype polymorphism has an effect on language and schizophrenia. Interactive effects of genotypes of COMT and IL-10 were significant in schizophrenia patients.
Punchaichira TJ et al. [16]	2020	Observational	1677	To study the effect of rs1076560 (DRD2) and rs4680 (COMT) on tardive dyskinesia and cognition in schizophrenia patients.	COMT rs4680 variant was associated with tardive dyskinesia. Smokers with this variant had an increased risk of tardive dyskinesia. This variant had a positive association with emotional efficiency in schizophrenia patients.
Bosia M et al. [17]	2019	Observational	135	To study the effect of interaction between cannabis use and COMT genotype variants in schizophrenia patients.	Met carriers performed better on cognitive tasks – processing speed and verbal fluency.
Kang Y et al. [18]	2019	Observational	108	To assess how COMT contributes genetically to DLPFC changes in first-episode schizophrenia.	The interactive effect between significant disease and COMT was seen in the left DLPFC. Resting-state functional connectivity was associated with affective blunting in Val/Val genotype.
Deji C et al. [19]	2021	Observational	801	To study the association of COMT and Alpha-1-adrenergic receptor gene polymorphisms with multiple phenotypes of heroin use disorder.	The subjects having the G allele of rs769224 COMT variant were prone to consuming higher dosages of heroin every day.
Jones JD et al. [20]	2019	Observational	36	To assess the contribution of opioid- and dopamine-related genetic polymorphisms to the abuse liability of oxycodone.	The "stimulated" effects of oxycodone were seen in COMT rs4680 variant.
Hooten WM et al. [21]	2019	Observational	298	To assess the effect of COMT gene variants on the likelihood of opioid use and the dose of the opioid in adults suffering from chronic pain.	Individuals with the Met/Met variant were more likely to use opioids than those with Val/Met variant. The dosage of opioids used was higher among the Val/Met and Met/Met genotypes than the Val/Val genotype.
Hooten WM et al. [22]	2019	Observational	142	To assess the effect of COMT rs4680 SNP on hyperalgesia induced by opioids in adults with chronic pain receiving opioid therapy.	Adults with Val/Met variant were found to be more hyperalgesic compared to Val/Val and Met/Met variants.
Kaminskaite M et al. [23]	2021	Observational	329	To assess the effect of ANKK1-DRD2 and COMT SNP on the risk of alcohol abuse.	Having both genetic polymorphisms of COMT and ANKK1-DRD2 was associated with an elevated risk of hazardous use of alcohol.
Lovallo WR et al. [24]	2019	Observational	480	To assess the likelihood of alcohol and drug use in people who experienced ELA in the presence of a COMT genotype.	People with Val/Met or Met/Met variant of COMT who had exposure to ELA were more vulnerable to risky drinking behavior.
Saloner R et al. [25]	2020	Observational	122	To assess how the different COMT genotypes alter the effects of methamphetamine dependence on executive function.	Lower dopamine levels were found in Met/Met METH+ men with a worse performance of EF.
Cherner M et al. [26]	2019	Observational	149	To determine the effect of COMT genotype in methamphetamine-related executive dysfunction.	In people with methamphetamine dependence having the Val allele, executive function is protected.