Medical marijuana dispensaries were legalized here four years ago, but officials with Maine’s largest distributor say even as the drug becomes one of the state’s largest cash crops, the growth of the industry is hampered by the federal prohibition of pot.

And that’s even without the specter of federal prosecution, as U.S. Justice Department officials have followed a hands-off approach to enforcement in states where medical cannabis is legal and subject to strong local oversight.

The list of underreported byproducts of the clash between state and U.S. marijuana laws goes on and on, said Patricia Rosi, chief operating officer of Wellness Connection of Maine, far and away the state’s largest dispensary operator.