Plans are moving forward to convert a portion of a historic house first built more than 200 years ago in Harvard Square into a place for registered patients to purchase medical marijuana products.

The Cambridge Planning Board on Feb. 28 voted in favor of a special permit for Healthy Pharms Inc., to operate a dispensary at The Red House, a restaurant packed tightly among other businesses along pedestrian-friendly Winthrop Street.

The plan was opposed by a smattering of neighbors during a recent public hearing, with some worrying that the dispensary could fast become a place to purchase the drug for recreational use and others contending it would cause “irreparable’’ harm to abutters.

But many in Cambridge have been supportive of the proposal.

Nathaniel Averill, executive director of Healthy Pharms Inc., said the operation in Harvard Square would be discreet and feature tight security, and cater only to patients who rely on the drug to ease ailments.

“I think there are always concerns, no matter where you go,’’ he said. “But we have done a number of things, and we are trying to work with the local community groups as best we can.’’

The Red House, built in 1802, is run by restaurateur Paul Overgaag, who is also Averill’s business partner.

Plans for the dispensary call for downsizing the restaurant and turning the current side entrance into a hallway that would lead to a “mantrap’’ — a security checkpoint — and then toward the back of the building to a sales floor where medical pot could be purchased only by patients registered with the state.

Part of the restaurant’s second floor, currently devoted to rooms for events and dining, would become offices for dispensary staff and security, Averill said. The Red House would remain a restaurant with a downstairs dining area, bar, fireplace, and patio space.

Averill said the restaurant and dispensary would be separate entities and that the exterior of the historic house, with its white trim windows and dark shutters, would only see the addition of a few security cameras.

Once the Planning Board files its decision with the city clerk’s office, there is a statutory period during which it can be appealed.

Before it can officially open, the nonprofit must still win approvals from the state’s Department of Public Health, the agency that regulates medical marijuana facilities, as well as building permits and a certificate of occupancy from Cambridge officials.

Averill said an opening date has not been set for the dispensary, but he and Overgaag hope it’s by the end of this year.

Steve Annear can be reached at steve.annear@globe.com. Follow him on Twitter @steveannear.