Lawmakers in the US who support the relaxation on marijuana laws sparred with Obama administration officials who continue to label the drug in the same high-danger category.
The Drug Enforcement Administration's chief deputy said marijuana deserved to remain listed as a "Schedule 1" narcotic -- a list which includes severely addictive drugs including LSD and ecstasy -- even though he could not identify a single fatal overdose attributable to cannabis last year.
"Marijuana is the most widely available and commonly abused illicit drug in the United States," the DEA's Thomas Harrigan told a House panel in a joint statement with John Walsh, the US attorney in Colorado, which along with Washington state legalized recreational marijuana use this year.
They said abuse among young Americans is on the rise, with marijuana's more potent production methods and increased trafficking by international drug cartels the growing concerns.
But lawmakers were dumbfounded at a multi-billion-dollar anti-drug strategy from Washington that leads to thousands of incarcerations for acts that have already been decriminalized in 20 states.
"We've locked people up. We're spending billions of dollars, and it's not working," House Democrat Earl Blumenauer said.
Around 750,000 Americans were arrested on marijuana charges in 2011, outpacing detentions for violent crime, Blumenauer said citing FBI figures.
He and fellow member Steve Cohen said 16,000 people died last year from prescription drug overdoses, and noted how thousands more died from heroin, methamphetamines, cocaine and the legal intoxicant alcohol.
But when asked how many people died from marijuana, the DEA's Harrigan told the House government oversight panel: "I'm not aware of any."
The hearing was held just as Washington DC's city council ruled to decriminalize marijuana, ranking possession of small amounts of the drug on a similar scale as getting a parking ticket in the nation's capital.
Several lawmakers have argued that bringing pot sales within the US legal framework would allow authorities to tax and closely monitor the drug.
But Harrigan insisted that "there are no sound scientific, economic or social reasons to change our nation's marijuana policy."
Cohen said US marijuana legislation is so universally decried as wrong that "it breeds disrespect for the law" and the judiciary system as a whole.
"The idea that it's a schedule 1 drug is ludicrous," he added.
Subcommittee chairman John Mica noted that distinct conflicts between the federal law and state initiatives like those in Colorado needed to be resolved.
"We are trying to sort this out," Mica said, noting that while there has been success in reducing tobacco use rates, "we're backsliding on marijuana," with pot use among high school seniors rising by 19 percent since 2008.
Democrat Gerry Connolly, meanwhile, warned that US marijuana policy had racial overtones, citing figures showing blacks were four times more likely than whites to be arrested on marijuana charges.
"This level of disparity is indefensible," he said.