Background:Clinically significant herb-drug interactions have been previously documented and can be pharmacodynamic and/or pharmacokinetic in nature. Pharmacokinetic interactions have been attributed to induction or inhibition of either metabolic enzymes or efflux transporters. Objective: The effect of gel and whole leaf materials from three different aloe species namely Aloe ferox, Aloe marlothii and Aloe veraas well as polysaccharides precipitated from the A. vera materials on the bi-directional transport of cimetidine across rat intestinal tissue was investigated. Materials and methods:Cimetidine transport studies were performed across excised rat intestinal tissue mounted in Sweetana-Grass diffusion chambers in both the apical-to-basolateral and basolateral-to-apical directions. Results: While A. vera gel and whole leaf materials did not inhibit the efflux of cimetidine, the polysaccharides precipitated from them did show a reduction of cimetidine efflux. On the other hand, both A. ferox and A. marlothii gel and whole leaf materials exhibited an inhibition effect on cimetidine efflux. Conclusions: This study identified a modulation effect of efflux transporters by certain aloe materials. This may cause herb-drug pharmacokinetic interactions when drugs that are substrates for these efflux transporters are taken simultaneously with aloe materials. On the other hand, these aloe materials may be used for drug absorption enhancement for drugs with low bioavailability due to extensive efflux.