Various in vitro methods utilize different biological barriers to study drug absorption.

In the diffusion cell technique, a donor compartment with the drug solution and a synthetic or natural GI membrane connect to a receptor compartment containing a buffer solution. Analysis of the drug in the receptor compartment can indicate absorption.

Similarly, in the cell culture technique, Caco-2 cells grown on collagen -treated synthetic polycarbonate membrane, models the intestinal barrier and serve as an interface to the receptor compartment.

The everted sac technique uses an inside-out and buffer-filled small intestinal segment of the laboratory animal. The sac is then placed in a drug-containing buffer, shaking gently at 37 degrees Celsius. Measuring drug content in the segment's buffer can determine the drug's absorption.

Lastly, the everted ring technique involves thin rings of everted rat intestinal segments placed in the drug-containing buffer at 37 degrees Celsius. Post-incubation, rings are dried and weighed, and drug analysis is done to determine drug absorption.