In this study, a pharmacokinetic simulation model was used to explore the dissolution acceptance criteria for BCS I and III biowaivers and to examine the risk of MDR-1 efflux transporter on bioequivalence of substrates. The compartmental absorption and transit (CAT) model with one- or two systemic compartments was used. The parameter values used in the simulations were based on the pharmacokinetics of existing 70 BCS I and III drugs. Based on the simulations BCS I drug products with Tmax of > 0.9 h, both dissolution criteria "very rapid" and "rapid and similar" were acceptable. For rapidly absorbed and distributed BCS I drug products with Tmax of 0.6-0.9 h, the dissolution criterion "very rapid" is preferred. If Tmax is less than 0.6 h there is a risk of bioinequivalence for the BCS I drug products regardless of the dissolution criteria. Based on the simulations, all BCS III drug products were good biowaiver candidates with both dissolution criteria. Almost all the BCS III drug products (> 89%) and many BCS I products (9-57%) showed risks of bioinequivalence, if an excipient in either product inhibits MDR1-efflux transport of the drug. To eliminate these risks excipients with prior use in bioequivalent products should be used for MDR-1 efflux substrates.