Denver prosecutors will no longer charge those 21 and older for carrying less than an ounce of marijuana, and will review current cases that fit under the language of a recently voter-approved state constitutional amendment.

District Attorney Mitch Morrissey and City Attorney Doug Friednash made their decision Thursday, a day after Boulder County District Attorney Stan Garnett made headlines when he announced his office will dismiss any pending cases that deal with less than an ounce of marijuana.

Amendment 64 passed by a more than 2-to-1 margin in Boulder County, and Garnett said such support makes it difficult to seat a jury in possession and paraphernalia cases. The measure legalizes possession of up to 1 ounce of marijuana by anyone over age 21.

There are about 70 cases pending in Denver that would fall under the amendment, Denver district attorney spokeswoman Lynn Kimbrough said Thursday. As those cases go through the court system, they will be reviewed for possible dismissal. This won’t apply to cases where there is another charge or when the person is under age 21, she said.

People who think their case may be dismissed still must appear at their court date, Kimbrough said.

In Denver, Amendment 64 passed with about 66 percent support.

Statewide, the ballot measure — which is set to go into effect 30 days after votes are certified following the Nov. 6 election — passed with 55 percent of voter support.

In Arapahoe County, the amendment received about 53 percent support, and Sheriff Grayson Robinson said his office will meet early next week with the 18th Judicial District attorney’s office to discuss the matter.

This year, Robinson’s office has issued an average of 43 summonses each month for marijuana possession and paraphernalia. By contrast, in Boulder County, five to 20 cases pass through Garnett’s office each month.

“We are evaluating the issues related to the passage of the constitutional amendment to ensure that required modifications to policy and the application to our operations are implemented in a well-considered manner,” Robinson said.

Weld County District Attorney Ken Buck, a staunch opponent of Amendment 64, said in a statement Thursday that his office has an obligation to prosecute offenses that were crimes at the time they occurred.

“Accordingly, we will not be dismissing existing marijuana-possession cases,” he said. “But more importantly, our office prosecutes low-level possession cases to get drug users help with their addictions. That practice will continue until state law changes.”

Voters in the northern Colorado county approved Amendment 64 by a little more than 600 votes.

Grand Junction and Palisade cops are no longer citing people for possession of less than 1 ounce.

Prosecutors in Larimer, Jefferson and El Paso counties have not changed how they deal with summonses and the prosecution of minor marijuana offenses.

In the 17th Judicial District, which includes Broomfield and Adams counties, officials are dealing with possession cases on a case-by-case basis.

Even when the law goes into effect, it won’t make much of a difference to the North Metro Drug Task Force, Sgt. Jim Gerhardt said. “That was just a summons; we weren’t arresting anyone for that anyway.”

However, Gerhardt said investigations of growing operations — where illegal sellers of marijuana raise plants — will be “severely impacted by Amendment 64. We saw people exploiting loopholes with the medical-marijuana laws, and there is going to be an exploitation of loopholes now too.”

Amendment 64 allows adults to grow up to six marijuana plants in their homes.

Gerhardt said that as investigators encounter locations with more than the allowed number of plants, they won’t be able to automatically shut them down.

“There’s nothing that prohibits 100 people from combining each of their six plants in one grow facility,” Gerhardt said. “It’s just how many 21-year-olds or older will you have claiming the plants. You do not even have to be a resident of the state or of the U.S.”

Kurtis Lee: 303-954-1655, klee@denverpost.com or twitter.com/kurtisalee

Denver Post staff writers Tom McGhee and Jordan Steffen contributed to this report.