DENVER—Marijuana consumers in Colorado could be in store for purchasing limits well below what they’re allowed to have.

A state task force set up to regulate recreational weed in Colorado agreed Monday to recommend marijuana purchasing caps. Adults over 21 in Colorado are allowed to have up to an ounce of weed, but the task force recommended that a single transaction at a pot shop be capped at a lower amount.

“This just empowers us to prevent diversion” of the drug to kids and others who can’t have marijuana, said Christian Sederberg, a lawyer and marijuana activist on the task force.

Regulators did not agree what the smaller cap should be, punting that decision to the state Legislature, which will ultimately decide all of Colorado’s marijuana rules.

Commercial pot sales in Colorado could begin by next year after state voters decided to flout federal drug law and permit adults to have small amounts of it.

The marijuana purchasing cap was suggested by Colorado Deputy Attorney General David Blake, who argued that Coloradans should face the same pot-shop purchasing caps as out-of-state visitors, a decision made last week.

Blake declined to explain the cap to reporters after the task force meeting. Attorney General John Suthers was a prominent opponent of marijuana legalization, which voters here approved by a wide margin despite legal warnings about violating federal drug law.

Sederberg said marijuana legalization backers agreed to purchasing limits because he said most pot users won’t find it onerous. Sederberg said average daily pot smokers use about half a gram a day, well below the 1 ounce possession limit.

Sederberg compared pot limits to kegs of beer. There’s no limit on alcohol possession, but people seeking kegs of beer must sign their names and agree not to share beer with minors, Sederberg pointed out.

The task force also agreed to labeling requirements to include potency. Marijuana regulators decided that the drug’s potency can’t be capped—but pot should be clearly labeled so consumers know its strength.

The labels would have to state the amount of THC, marijuana’s psychoactive ingredient. Pot would also have to carry labels stating “there may be health risks associated with the consumption of this product.”

“The idea is to warn people about the dangers of ingesting marijuana,” said Jack Finlaw, a lawyer for Gov. John Hickenlooper and co-chairman of the task force.

The state Legislature will ultimately decide whether to try potency limits.

The same task force voted last week against a residency requirement for adults over 21 buying marijuana. If adopted, that recommendation would open the door for marijuana tourism.

The task force failed to agree how to test pot for banned toxins such as pesticides and herbicides. The task force agreed broadly that testing requirements should be set later, but they couldn’t agree how often pot strains should be tested or who should certify the tests.

The task force has less than a week to settle regulations. Anything the group can’t agree to will be punted to the state Legislature and the state Department of Revenue, which will oversee Colorado’s eventual commercial pot industry.

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Online:

Amendment 64 task force: http://www.colorado.gov/cs/Satellite/Revenue-Main/XRM/1251633708470