People who register with the state of Ohio to legally use medical marijuana will be prohibited from possessing firearms under federal law, according to guidance released by the U.S. Bureau of Alcohol, Tobacco and Firearms.

In an open letter to federally licensed firearms dealers, the ATF advised in 2011 that marijuana is still a Schedule I controlled substance under federal law so any use of the drug is unlawful, and gun dealers are prohibited from providing guns or ammo to anyone they have cause to believe uses pot.

“There are no exceptions in federal law for marijuana purportedly used for medicinal purposes, even if such is sanctioned by state law,” the memo says.

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The law applies to more than just buying guns. The ATF letter says marijuana users are prohibited from “shipping, transporting, receiving or possessing firearms or ammunition.”

Anyone applying to purchase a gun from a licensed dealer must sign a form attesting he or she is not “an unlawful user of, or addicted to, marijuana or any depressant, stimulant, narcotic drug, or any other controlled substance.”

“Warning: The use or possession of marijuana remains unlawful under Federal law regardless of whether it has been legalized or decriminalized for medicinal or recreational purposes in the state where you reside,” the form notes.

Lying on the form is a felony under federal law, punishable with up to 10 years in prison.

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“There is definitely a conflict between the state laws and the federal laws,” said Joe Eaton, southwest Ohio spokesman for the Buckeye Firearms Association.

It’s not clear how to reconcile that conflict, he said, “We are confused as everyone else at this point.”

When Ohio’s medical marijuana program becomes operational in September 2018, Ohioans will be able to register to use cannabis if they have a recommendation from a physician saying they have one of 21 qualifying conditions.

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Industry analysts have estimated as many of 24 percent of the state’s population – or about 2.8 million Ohioans – have a qualifying condition.

The conflict between federal firearms laws and state cannabis laws has flared up on other states.

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In Hawaii, Honolulu police last month told residents who had medical marijuana cards they have 30 days to turn in their firearms to authorities, according to reports in the Honolulu Star Advertiser.

The Associated Press reports that a federal circuit court of appeals ruling on a case out of Nevada found that the federal ban on the sale of guns to medical marijuana users doesn’t violate the Second Amendment.