Sen. Rand Paul, R-Ky., takes questions Monday, July 1, 2013, from about 40 Owensboro Tea Party members in Owensboro, Ky. (The Messenger-Inquirer, Gary Emord-Netzley/AP)

Ahead of his Thursday visit to Nevada, Sen. Rand Paul, R-Ky., reiterated his personal opposition to marijuana use. Pro-pot activists say Paul is spreading misinformation about the drug.

"I personally think that marijuana use is not healthy," Paul told the Las Vegas Sun in an interview published Wednesday. "People that use it chronically have a loss of IQ and a loss of ambition, but at the same time states have the right to make these decisions."

Marijuana activists tell U.S. News that Paul's claims about ambition, health and IQ are wrong.

"It's unfortunate, but Senator Paul is basing his opinion about marijuana on "Reefer Madness"-fueled fear-mongering instead of sound science," said Kris Hermes, a spokesman for Americans for Safe Access, a group that lobbies in favor of medical marijuana. "Contrary to Senator Paul's unscientific assessment... there are more than 200 peer-reviewed studies that clearly show marijuana's medical efficacy."

Hermes speculated that "Paul and others' lack of education is the primary cause of our federal marijuana policy, based more on emotion and moral indignation rather than public health and medical science."

NORML Executive Director Allen St. Pierre told U.S. News Paul's approach to the issue is "either pandering, or some really smart coalition-building" in favor of drug policy reform.

St. Pierre disagrees with Paul's claim that marijuana is broadly harmful to health, pointing to a study published by the Annals of the American Thoracic Society in June by UCLA medical school professor Donald Tashkin. That study found light or moderate marijuana use isn't associated with a higher risk for lung cancer.

"Even with long-term heavy amounts [of marijuana] there is little effect on long-term cognitive functions," St. Pierre added.

"It was unfortunate, because Mr. Rand on the one hand is very critical of the drug war, but he wants to buffer his support by declaring, 'I don't smoke marijuana, I don't want my son to smoke marijuana, I don't want my dog to smoke marijuana,'" St. Pierre said. "He's carving out this fascinating position here."

Mason Tvert, communications director of the Marijuana Policy Project, told U.S. News Paul likely based his IQ claim "on a study that has been thoroughly debunked based on flawed methodology." That study's findings, published in July 2012 by the Proceedings of the National Academy of Sciences, were disputed by scientists who said the findings could be explained entirely by socioeconomic factors.

"As for loss of ambition, he himself used marijuana," Tvert claimed. A 2010 article in GQ magazine alleged Paul used pot while a student at Baylor University. "Every objective study on marijuana has concluded that it is far less harmful than alcohol to the consumer and to society," he said. "Marijuana is far less toxic and less addictive than alcohol, and unlike alcohol, it does not contribute to violent and reckless behavior."

This isn't the first time Paul, a likely 2016 presidential candidate, has tried to please both sides of the drug policy debate. Highlighting the perceived sloth and listlessness of heavy marijuana users seems to have become a key talking point for the senator.

"I don't really believe in prison sentences for these minor, non-violent drug offenses," Paul said in a June 4 discussion with the Hoover Institution, "but I'm not willing to go all the way to say it is a good idea either. I think people who use marijuana all the time lose IQ points, I think they lose their drive to show up for work."

During an April 10 event at Howard University, Paul said, "I think that if you use it too much you will lose IQ points, I think if you use it too much you won't show up for class, I think you'll eat too many Doritos." He added: "I will do everything I can to keep non-violent criminals out of jail."

In May, Paul told the Washington Post, "I'm not advocating everyone go out and run around with no clothes on and smoke pot. ... I'm not a libertarian. I'm a libertarian Republican. I'm a constitutional conservative."

Paul is often thought of as one of the most marijuana-friendly politicians, but his approach to advocating drug policy reform is notably more nuanced than the fiery denunciation of drug prohibition that was a libertarian crowd-pleaser during the 2008 and 2012 presidential campaigns of his father, former Texas Rep. Ron Paul.