SLCO1B1*23 is assigned no function based on limited evidence in heterozygous patients and in vitro studies. A clinical study of 1 heterozygous carrier of *23 showed markedly decreased high-dose methotrexate clearance compared to wildtype, slower than a *5/*5 patient (22147369). In vitro uptake was severely diminished compared to wildtype (22147369). Computational activity predictions support the in vitro and in vivo data (22147369).Therefore, consensus among experts was no function with limited evidence.