SLCO1B1*37 is assigned normal function based on strong evidence in heterozygous and homozygous individuals. The plasma levels of highly sensitive OATP1B1 endogenous substrates GCDCA-3G, GDCA-3G and CPI are slightly and non-significantly lower in SLCO1B1*37 homozygotes (32961594, 32961019). In vitro studies have mostly demonstrated unaltered activity compared to SLCO1B1*1 (11477075).