joe biden Associated Press/John Locher

Former Vice President Joe Biden says his questions over marijuana’s reputation as a gateway drug are holding him back from supporting legalization.

Biden said at a Saturday town-hall event that „there’s not nearly been enough evidence“ to confirm whether marijuana is a gateway drug, evidence he said he would need before supporting federal legalization.

There has been research on the issue, however, and it has repeatedly failed to find solid evidence that marijuana leads people to harder drugs.

The former vice president’s openness to medical marijuana and state-specific policies is a change from his past, but his reluctance still separates him from other Democratic presidential candidates, most of whom openly support nationwide legalization.

Visit Business Insider’s homepage for more stories.

Former Vice President Joe Biden has doubled down on his reserved stance over marijuana and says his questions over its status as a gateway drug are holding him back from supporting federal legalization.

Biden was speaking at a Las Vegas town hall on Saturday when he said there had „not nearly been enough evidence“ to confirm whether marijuana was a gateway drug, evidence he said he would need before supporting federal legalization.

„The truth of the matter is, there’s not nearly been enough evidence that has been acquired as to whether or not it is a gateway drug,“ Biden said. „It’s a debate, and I want a lot more before I legalize it nationally. I want to make sure we know a lot more about the science behind it.“

Though he didn’t support overturning federal law right away, Biden said he thought states „should be able to make a judgment to legalize marijuana.“

He added that he also supported medical marijuana and that possession of the substance „should not be a crime.“

Biden’s most recent comments signaled a much softer approach from that during his 40-year career in the Senate, much of which overlapped with the government’s war on drugs, specifically in designing strict criminal penalties for nonviolent drug users.

His campaign has since said in announcing a massive criminal-justice-reform plan, which included decriminalizing marijuana, that he wants to cut down on rates of incarceration and fix racial, gender, and income-based disparities in the system. He also said in a June campaign speech that he supported expunging possession convictions.

Still, Biden on Saturday again stopped short of backing federal legalization of recreational marijuana, calling for increasing the amount of scientific research into the drug.

„It is not irrational to do more scientific investigation to determine, which we have not done significantly enough, whether or not there are any things that relate to whether it’s a gateway drug or not,“ Biden said.

National organizations have not been as suspicious of marijuana as Biden has, however, and have found no solid evidence to support the claim that using marijuana leads to the use of harder drugs. A 1999 Institute of Medicine report said marijuana „typically precedes rather than follows initiation of other illicit drug use“ but „does not appear to be a gateway drug to the extent that it is the cause or even that it is the most significant predictor of serious drug abuse; that is, care must be taken not to attribute cause to association.“

The National Institute on Drug Abuse says research shows „the majority of people who use marijuana do not go on to use other, ‚harder‘ substances,“ and drug use can be affected by numerous other biological and environmental factors.

Biden’s stance, perhaps designed to soften his image as related to marijuana, still generally separates him from today’s Democratic presidential candidates, most of whom openly supporting nationwide legalization.