"The issue of purchasing medical marijuana is an emerging issue, and we're continuing to look into it," says Jim Issokson, a spokesman for MasterCard.Want to Charge Weed? What Credit Card are You Carrying?
Visa and Discover also allow people to purchase medical marijuana in states where it's legal. Citing the fact that marijuana-medical or not-is still illegal according to federal law, American Express does not allow its customers to use its cards for pot purchases of any kind.
"It is our policy to adhere to the federal law in such matters," Bradley R. Manor, an AmEx spokesman, told Smartmoney.com.