Thousands of people have signed a Minnesota company's petition to Google, asking the search engine to accept online ads for medical marijuana.

Minnesota-based Vireo Health has been trying for months to get Google to accept ads for a string of clinics it operates in New York. But Google rejected each ad, citing its policy against promoting "dangerous products or services."

So Vireo — the parent company of Minnesota Medical Solutions, one of this state's two designated medical cannabis retailers — circulated a petition on Change.org, asking the company to reconsider. As of Friday afternoon, the petition had more than 13,000 signatures from across the country.

"Google's policy is baffling," the petition reads in part. "Google willingly accepts ads that promote highly addictive painkillers, like OxyContin, that are responsible for thousands of deaths each year, but rejects medical cannabis ads that could, in many cases, be a significantly safer therapeutic option for patients."

Dr. Kyle Kingsley, the Minnesota emergency room physician who co-founded Vireo and MinnMed, said Google has not responded since its initial rejection in March. Google has a long-standing ban on ads for products such as tobacco, explosives and recreational drugs.

"The vast majority of the populace is on our side in this," Kingsley said. "Google's a good company. I'm surprised they have a policy like this. I think they'll change, I really do … I don't know if we have to get 15,000 signatures, or what it will take. This is about patient access."

Medical marijuana is legal in 24 states, but Google's ad ban is unlikely to put much of a dent in its bottom line — Google took in $19.1 billion in ad revenue in the first quarter of this year.

Kingsley said Vireo has no way of knowing what effect the ad ban is having on its clinics. The Google blackout is just one hurdle marijuana start-ups face in a country where the federal government still considers cannabis an illicit drug with no recognized medical value. Banks and credit card companies are reluctant to do business with companies that grow and sell marijuana, and those companies also miss out on business tax breaks.

Minnesota and New York have similar restrictive medical marijuana programs, and clinics in both states have struggled to bring in customers. Both limit who can use medical marijuana, who can sell it and in what form. Almost a year after legalization, there are 1,324 patients enrolled with Minnesota's Office of Medical Cannabis.

"We would love to be able to advertise there, for people looking for treatment for their chronic pain," Kingsley said.

In August, Minnesota clinics will open their doors to patients suffering intractable pain that has not responded to standard treatments or therapies. To get into the program, patients need their doctor to certify to the state that they have one of the handful of critical or terminal illnesses that the state has approved for treatment with medical marijuana. Right now, those conditions range from seizure disorders and certain cancers to AIDS and Crohn's disease.

Once certified, patients often face long drives to one of three clinics currently operating in the state, and the sticker shock of paying for medication priced well above street value. The price of a month's supply of medical cannabis in Minnesota can range from less than $100 to well over $1,000, depending on the patient and their condition. No insurance will cover the cost of a marijuana prescription. Minnesota allows marijuana to be sold only as pills or liquids. Smoking the plant itself remains illegal.

Bringing in pain patients could potentially bring in thousands of new customers, which could help drive down prices. Advocates hope it could also lead to a drop in deaths from prescription painkillers. A 2014 study in the Journal of the American Medical Association reported a sharp decline in narcotic overdose deaths — a drop of up to 25 percent in some cases — in states with medical marijuana programs.

You can read Vireo's petition at www.change.org/p/google-accept-medical-marijuana-ads