Another way in which medications may interact with one another is through their effect on drug transport systems, especially the P-glycoprotein (P- gp) system. The P-gp transporters transport medications and metabolites out of the central nervous system and brain through the blood-brain barrier into the blood. The activity of P-gp transporters can significantly impact the effect of drugs such as morphine, oxycodone and methaone on the brain by reducing their levels in the brain. Early findings indicate that CBD significantly inhibits P-gp-mediated drug transport, suggesting CBD could potentially increase brain levels of morphine and other opioids that are P-gp substrates thus enhancing their impact. CBD may also influence the absorption and disposition of other coadministered compounds that are P-gp substrates.