The DRD2 gene encodes the dopamine D2 receptor which is the main target for many antipsychotic medications.

A1 Allele Carriers (A1/A1 variant): Individuals with the A1 allele have reduced D2 receptor density in brain regions such as the striatum, which can lead to heightened sensitivity to the antagonistic effects caused by Antipsychotics on the D2 receptor. As a result, these individuals are more likely to experience extrapyramidal symptoms (EPS) such as tremors, rigidity, and akathisia, even at low doses. Overall, those who carry the A1 allele of the DRD2 gene may require dose adjustments or other therapies to avoid these side effects as EPS such as TD which can be permanent.