A medical marijuana prescriber and patient is challenging President Donald Trump’s administration over a federal statute barring cannabis users from purchasing or owning firearms, even when they take the drug legally pursuant to state law.

In April, Philadelphia-based doctor Matthew Roman went to a local gun store with plans to buy a revolver for self-defense. Pennsylvania is one of more than 30 states that have legalized marijuana for medicinal use, and Roman is licensed to prescribe cannabis to qualifying patients in his state. He also has a card that allows him to use the plant to treat symptoms of post-traumatic stress disorder.

Although Roman has “no other record of violence, criminal activity, or mental disorder,” according to the suit, when he went to purchase the handgun, a clerk informed him that his status as a medical marijuana patient meant he could not legally obtain a firearm.

Under the 1968 Gun Control Act, any “unlawful” user of a controlled substance is also prohibited from purchasing or owning a gun. Federally licensed gun dealers must ask prospective customers about their drug use habits before approving a purchase. And because marijuana remains a Schedule I substance under federal law, the U.S. government maintains there is no way to use cannabis lawfully.

In 2016, a federal appeals court ruled that this prohibition did not violate the Second Amendment rights of a Nevada medical marijuana patient who was turned down by a gun store after trying to buy a firearm in 2011.

Roman’s suit, filed last week, alleges that federal law violates his Second Amendment right to gun ownership and his Fifth Amendment right against self-incrimination (because federal firearm transaction forms require medical marijuana patients to report that they use the drug “unlawfully,” even when it’s sanctioned under state law). The complaint specifically names acting Attorney General Matthew Whitaker and the directors of the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives.

A spokesperson for the U.S. Attorney’s Office for the Eastern District of Pennsylvania, where the suit was filed, declined to comment on the case.

You have alcoholics who are not prohibited from owning firearms. John Weston, attorney for plaintiff Matthew Roman

Attorneys for Roman say the restriction on gun ownership for medical marijuana patients is in part the result of decades of “cannabis propaganda,” which they argue has led to inaccurate claims about the herb being associated with violent behavior.

The federal government is “advancing an interpretation of the law which automatically assumes that medical marijuana patients, by operation of the method of treatment for their illnesses, are prone to engage in gun violence in the same manner as those adjudicated mentally ill or those who have been convicted of a felony,” the complaint alleges. Ex-offenders and individuals who have been adjudicated as mentally “defective” or committed to a mental institution are also legally barred from gun ownership.

The complaint goes on to note that federal law treats marijuana differently than it does other approved treatments for PTSD, such as Ambien, as well as legal recreational drugs like alcohol ― both of which are known to carry more substantial risks than cannabis.

“You have alcoholics who are not prohibited from owning firearms,” attorney John Weston told HuffPost. “Ambien has side effects that are arguably much worse than those of medical marijuana, and yet a person who’s being prescribed Ambien for this same condition has the absolute constitutional right to own a firearm for self-defense in his home.”

The question, Weston said, is why the federal government is “picking on medical marijuana ... when it’s much less harmful than any of the other medicines you can use to treat this condition.”

ASSOCIATED PRESS Photographs of marijuana plants on the wall of a Pennsylvania medical marijuana dispensary. A Philadelphia-based doctor and cannabis patient is challenging a federal law that bars legal medical marijuana users from gun ownership.

The strict nature of Pennsylvania’s medical marijuana law, which carefully controls the drug “from seed to consumer,” should be enough to tamp down the government’s concerns about the plant’s potential nexus to crime, Weston added.

In light of that, he expressed confidence that Roman’s suit would have a better chance than the previous 2016 ruling, issued by 9th U.S. Circuit Court of Appeals in San Francisco. Victory could take a number of different forms, said Weston, ranging from a narrow ruling affecting only Roman to one that could more broadly upend federal firearms restrictions on medical marijuana patients.

For cannabis advocates, a change to rules about medical marijuana and gun ownership is long overdue.

“There is no credible justification for a ‘marijuana exception’ to the U.S. Constitution,” Paul Armentano, deputy director of the National Organization for the Reform of Marijuana Laws, said in a statement to HuffPost. “Responsible adults who use cannabis in a manner that is compliant with the laws of their states ought to receive the same legal rights and protections as do other citizens.”

Armentano went on to urge Congress to pass legislation to federally decriminalize marijuana “in a way that comports with both public and scientific opinion, as well as its rapidly changing legal status under state laws.”

Read the entire complaint below.