Vireo Health of New York is telling straphangers to "Ask your doctor about medical marijuana" as part of a monthlong ad campaign that launched Monday in nearly 100 city subway stations.

"New Yorkers have new options for chronic pain," reads each poster, along with Vireo's logo and website. The campaign, designed by Minnesota-based ad firm Replace, includes four versions of the poster featuring people of different ages and ethnicities.

"There's obviously still a lingering stigma associated with medical marijuana, and we think by advertising in the subway system alongside more traditional products, this will help address the stigma," said Ari Hoffnung, chief executive of Vireo Health of New York, one of the five medical marijuana companies currently licensed in the state.

Vireo's recent launch of its cannabis delivery service to customers throughout the five boroughs made it the right time to kick off a citywide campaign, Hoffnung said.

Hoffnung said he has seen an uptick in customers since the state began allowing patients with chronic pain to get cannabis cards in March. But, he added, "the market is still incredibly small when you benchmark enrollment on a per capita basis."

And with the state looking to license five new medical marijuana companies in the coming weeks—a move Vireo and other cannabis companies are contesting in court—competition for those customers is set to increase.