America's gun control laws could take a huge bite out of the medical marijuana industry if they were enforced. According to the Gun Control Act of 1968, it is illegal for cannabis users to buy or even possess a firearm. That means even medical marijuana patients are breaking the law if they own a gun.

The obscure law doesn't come up very often, but it made headlines earlier this month following a ruling from the 9th U.S. Circuit Court of Appeals, which holds jurisdiction over nine Western states, including California, Oregon and Nevada. The court was settling a challenge to the law based on the argument that denying cannabis users the right to bear arms was unconstitutional because the ban violated the Second Amendment. But the judges unanimously disagreed, so the law remains on the books.

However, Michael Hammond of the activist group Gun Owners of America (GOA) told Civilized that it is hardly enforced. So cannabis users aren't supposed to own firearms according to federal law, but many do anyway.

That conflict made Marijuana Business Daily wonder what sort of financial impact the law could have on the medical marijuana industry if it were enforced. To figure that out, they zeroed in on those nine states and used the number of registered medical marijuana patients and the estimated percentage of gun owners in each state to approximate how many people would have to give up their cannabis cards in order to keep their firearms.

Arizona, Nevada would be hit especially hard

Based on those calculations, Arizona's medical marijuana market would lose the most money if the law were enforced. Dispensaries would see a shortfall of approximately $7.7-million -- or 3.4 percent of the $225-million that they are projected to make in 2016. But Nevada would be hardest hit because it has a small medical industry and a large population of gun owners. In actual dollars, the state would only lose about $1.9-million in sales if gun owners turned over their cards. But that is 6.3 percent of their projected revenue in 2016, which is a huge contraction for a small market.

Unfortunately, it's impossible to calculate the potential damage in larger markets like California because the number of patients is unclear. Registering as a medical marijuana user is voluntary in the Golden State, so guesstimates would be very rough. 

However, the biggest loss to all nine states could be the curtailed growth of their industries. As McVey notes, "These estimates do not account for the chilling effect the court’s ruling may have on potential new MMJ patients – deterring those still on the fence that want to maintain their right to legally purchase firearms."

In other words, if the law were enforced, current gun owners might decide against becoming medical marijuana patients for fear of losing their firearms. So the 1968 act might not violate an American's right to bear arms. But it might infringe on their ability to use medicine that can help treat multiple sclerosis, cancer and other serious health conditions.