Massachusetts voters are firmly in support of a November ballot initiative that would legalize the medical use of marijuana, according to recent poll results.

Fifty-eight percent of respondents favored the measure, while 27 percent were opposed and 15 percent were undecided. The poll, conducted by Public Policy Polling, a national firm based in Raleigh, N.C., surveyed 1,115 likely Massachusetts voters last month, asking them, “Question 3 would eliminate state criminal and civil penalties for the medical use of marijuana by qualifying patients. If the election was today, would you vote yes or no on Question 3?”

The results indicate increasing support for the measure; according to earlier PPP polls, in June, 57 percent of respondents were in favor and 33 percent opposed; in March, 53 percent favored the measure and 35 percent were opposed.

If passed by voters, the ballot question would protect patients and healthcare providers from punishment for medical use of marijuana. The drug would be available to patients suffering from a list of qualifying conditions, including cancer, glaucoma, AIDS, hepatitis C, ALS, Crohn’s disease, Parkinson’s disease and multiple sclerosis, with a written recommendation from a doctor. The marijuana would be available at nonprofit dispensaries registered with and overseen by the Mass. Department of Public Health. The law would allow up to 35 such dispensaries in the state, with at least one in each county and no more than five in any one county. DPH could also allow individuals to register to grow pot for personal medical use if they demonstrated a hardship that prevents them from accessing a dispensary.

If passed at the Nov. 6 election, the law would go into effect next January.

Medical marijuana is already legal in 17 states, including Connecticut, Maine, Rhode Island and Vermont, as well as in the District of Columbia.

Voters in Arkansas will also have the opportunity to legalize medical marijuana on the November ballot. Voters in Colorado, Oregon and Washington will vote on ballot questions that would go even further, legalizing marijuana use by adults.