MEXICO CITY (AP) — A new study by a respected Mexican think tank asserts that proposals to legalize the recreational use of marijuana in Colorado, Oregon and Washington could cut the profits of Mexican drug cartels by as much as 30 percent.

Opponents question some of the assumptions made in the Mexican Competitiveness Institute study, saying the proposals could also offer new opportunities for cartels to operate inside the U.S.

The ballot measures to be decided on Nov. 6 would allow adults to possess small amounts of marijuana under a regimen of state regulation and taxation.

Polls have shown tight races in Washington and Colorado, with Washington's measure appearing to have the best chance of passing.

Oregon's measure, which would impose the fewest regulations, does not appear likely to pass.