John Oliver returned on Sunday after a brief hiatus with a detailed story about America’s most counter-productive and antiquated marijuana laws.

In addition to detailing how the U.S. tax code screws marijuana businesses that operate legally within their states, Oliver showed how federal regulations put individuals who were complying with state laws at risk.

“If you have marijuana right now, even if you are acting completely legally according to your state, you may still be in serious jeopardy,” Oliver said. The “Last Week Tonight” host then went through numerous examples of how federal law interfered with people who had medical marijuana prescriptions to treat everything from epileptic seizures to PTSD.

“I know that some people will say, well hold on, the medical efficacy of marijuana needs a lot more study, and that is true,” Oliver said. “The problem is, it’s very difficult to do that because federal laws are standing in the way.”

Attorney General Jeff Sessions and President Donald Trump’s administration have hinted that the federal government may crack down on states that have legalized recreational marijuana use.

“I don’t think America is going to be a better place when people of all ages, and particularly young people, are smoking pot,” Sessions told reporters in February. “I believe it’s an unhealthy practice, and current levels of THC in marijuana are very high compared to what they were a few years ago, and we’re seeing real violence around that.”

Watch Oliver’s take-down, including his response to Sessions, in the video above.