The mother of a 22-year-old woman who died after overdosing on toxic heroin has shared a harrowing last photo of her daughter moments before she was taken off life support.

Cheryl Towery, 49, said she hoped the heartbreaking image of Elaina Towery lying in a coma in her hospital bed would serve as a wake-up call to other addicts and their families.

Ms Towery died on Monday at Sinai-Grace Hospital in Detroit, four days after she was found slumped in the toilet of a nearby Burger King.

She is thought to have taken heroin laced with fentanyl, a powerful synthetic opoid up to 100 times stronger than morphine that has been linked to thousands of deaths in the US.

The mother-of-one had battled addiction for seven years and overdosed five times.

She began taking heroin after getting into an abusive relationship with a man who was later convicted of domestic violence, according to her mother.

"She has a five-year-old son that she gave up due to her addiction because she wanted him to be in a better place," Ms Towery told local news channel Fox 2.

"[She was] beat up, being pimped out, being kept in a hotel room on heroin."

Cheryl Towery said daughter Elaina was her 'best friend' (Cheryl Towery/Facebook)

Elaina was found unconscious and in cardiac arrest by staff 25 minutes after going into the fast food restaurant's toilet in Thursday evening.

"I wasn't prepared for what I saw in the emergency room because that's the worst I've ever seen her," her mother said.

Elaina suffered liver and kidney failure and her muscles deteriorated. A scan on Monday showed no brain activity.

"She's my only daughter, my best friend. She was supposed to start her new job today, now she's on life support, " said Ms Towery before her daughter's death.