Medical marijuana users are accusing the federal government of violating their privacy and jeopardizing their safety after Health Canada sent out letters in envelopes that outed them as medical marijuana users.

Health Canada sent the letters to approximately 40,000 people across the country to inform them of changes to the Marijuana Medical Access Program beginning April 1.

Debbie Stultz-Giffin, who has a licence to grow marijuana in Nova Scotia, said any previous correspondence about the program came in plain brown envelopes and was sent by registered mail.

These letters were sent to approximately 40,000 medical marijuana users across Canada. (CBC)

The most recent letter, she said, was delivered in an envelope that referred explicitly to the Medical Marijuana Access Program and included her name and address on the envelope.

"I was instantly shocked and appalled to see the words 'medical marijuana' and 'Health Canada' exposed for everyone to see," Stultz-Giffin told CBC News on Thursday.

Stultz-Giffin said the letter explained changes are being made to the program because the "high value of marijuana on the illegal market increases risks of violent home invasion and diversion to the black market."

The letter, she argues, painted a target on her back and increased stress that medical marijuana users don't need.

"It certainly exposes patients to the risk of home invasions. It exposes us to the risk of neighbours perhaps having seen the mail and gossiping about our medical conditions," Stultz-Giffin said.

"It may change the way that neighbours and other community members view patients who use medical cannabis in the privacy of their own homes."

George Da Pont, the deputy minister at Health Canada, issued an apology on the Health Canada website and called it an administrative error.

"I have been advised that as the result of an administrative error, the envelopes were labelled to indicate that they were sent by the program. This is not standard Health Canada practice," he wrote.

"On behalf of Health Canada, I deeply regret this administrative error. Health Canada is taking steps to ensure this does not happen again."

Da Pont said the department was "in discussion" with the office of the privacy commissioner about the incident.

A spokeswoman for the privacy commissioner, meanwhile, told CBC News it wasn't Health Canada that told them about the breach.

"We were made aware of it by a number of concerned individuals who contacted our office. We have since received complaints and we will be investigating this matter," Heather Ormerod wrote in an email to CBC News.