LITTLE ROCK — A proposed ballot measure that would legalize marijuana for people 21 and older who want to participate in a statewide study on the drug’s medical and agriculture uses was rejected by Attorney General Dustin McDaniel on Wednesday.

McDaniel said the proposed initiated act was almost identical to one he rejected last year.

"I based my rejection upon the fact that the measure itself contained ambiguities that foreclosed me from accurately summarizing the proposal in a ballot title," he wrote. "I will not repeat the analysis I offered in my previous opinions. "I will further refrain from speculating what might have prompted you to submit for my review a proposal that is materially indistinguishable from a proposal I have rejected in the relatively recent past."

The Arkansas Cannabis and Hemp Study Act proposes a long-term and largely self-financed study on the medical use of marijuana and the agricultural use of hemp.

Tommy Cauley of Bee Branch, a spokesman for the group Arkansas Concerned Citizens, could not be reached for comment Wednesday.

McDaniel on Tuesday rejected a proposed constitutional amendment that would give people the right to privately grow and use marijuana, citing a number of ambiguities with the proposal submitted by Little Rock attorney John Wesley Hall of Little Rock, including that it refers to the medical benefits of marijuana even though it would not limit use to medical purposes.

Another proposal that would legalize marijuana for medical use in Arkansas was certified by McDaniel last month.

The group Arkansans for Responsible Medicine has until July 7, 2014, to collect 62,507 signatures of registered Arkansas voters in order to qualify its proposed initiated act for the November 2014 ballot.

Under the proposal, a patient with a doctor’s certification that he or she suffers from a malady included on a list of conditions that might be helped by marijuana could purchase the drug from dispensaries. The proposal would prohibit people from growing their own marijuana and allow it to be purchased only from state-regulated dispensaries.

The sale of marijuana would be subject to all state and local taxes and all of the taxes collected would be distributed equally among the Newborn Umbilical Cord Blood Bank, a newly created Arkansas Historic Preservation Fund, the Public Health Fund and the Behavioral Health Services Account Fund.

Also last month, the attorney general cited a number of ambiguities in rejecting a proposed initiated act by Arkansans for Compassionate Care to legalize medical marijuana. It was the fourth time since November that the group had its proposal rejected.

The group was successful in 2012 in getting its proposal on the ballot, but voters rejected the measure.