AUBURN — Police on Thursday were continuing to investigate a report that four strips of the prescription drug Suboxone were found in a Happy Meal bought at McDonald’s on Center Street the day before.

Police said a mother from Oxford spotted the drugs at the bottom of the box after she ordered chicken nuggets and fries for her 11-year-old son about 1:30 p.m. Wednesday.

“He ate most of the food and passed me the box and I look in it and found all that in there,” said Shirlee Marchesseault, the child’s mother. “I had to look up what that stuff was on Google because I didn’t know what it was!”

Nobody ingested the drug, police said, but the mother went back to McDonald’s and reported it at once. Auburn police are investigating the matter.

Suboxone is a prescription drug used to treat opioid dependence. It is used as a maintenance program mainly by people trying to quit heroin or other opiates.

The drug is often sold on the street or smuggled into jails and prisons, by people either trying to get off stronger drugs or seeking Suboxone’s opioid high. Drug officials say a single strip goes for about $8 to $10 on the street, but it will fetch up to $400 in correctional facilities.

Suboxone strips, which contain buprenorphine and naloxone, are typically dissolved under the tongue. Medical experts say accidental ingestion by a child could cause serious health problems or death.

By Thursday, there was no clear explanation as to how the strips — and a pen — ended up in the Happy Meal, but police were conducting interviews and reviewing other evidence.

Police were also working with representatives from McDonald’s and said the company was cooperating with their investigation.

Marchesseault said she was still angry long after making the discovery.

“My blood is boiling!” she said. “It’s crazy. My kid could have died.”

She said she had not been contacted by representatives from McDonald’s.

“I wanted to contact the food services and a district manager of McDonald’s,” Marchesseault said, “but I’m waiting for the investigation to go through before I do that.”

There have been reports of drugs found in fast food in the past, including marijuana in McDonald’s sweet tea in North Carolina and prescription pills found in an ice cream sundae in New Zealand.