Charlene McGregor, 41, died at the Queen Elizabeth University Hospital (QEUH) while being treated for a cyst behind her ear on March 12 of this year.
Her brother William, speaking to the Daily Record, said his sister’s body was left in the mortuary, with staff telling the family they “forgot about her”.
A toxicology screening later carried out by police found Ms McGregor died from a methadone overdose.
“She didn’t have the best life, but had been going with the same guy for ten years and was beginning to turn her life around,” her brother told the newspaper.
“We didn’t have much to do with her because of her drug issues, but she was on a methadone programme and her prescription had been reduced.
“She genuinely seemed to want to take steps away from drugs.
“But she shouldn’t have died the way she did and we still don’t know why it happened.
“The night before she passed away she had been asking the nurses to give her anything to help her sleep. That was at about 2am. By 6am, she was dead.”
After the family contacted the hospital, an emergency family meeting was called with clinicians, where they were told of the error.
“My partner and my mum went to it and were told ‘we can’t apologise enough’, that she was still in the mortuary and hadn’t been sent for a post-mortem,” Mr McGregor said.
“They said they forgot about her. Right away, the alarm bells started.
“They said because she had been lying there in a freezer for six weeks the post-mortem could come back inconclusive. And that’s exactly what happened.
“I can’t help wondering – if we hadn’t contacted them, would my sister still be lying there?”
Mr McGregor also questioned whether the delay had been deliberate and suggested a mistake may have been made in giving his sister, who had struggled with addiction but was taking steps towards recovery, the methadone that ultimately killed her.
A spokeswoman for NHS Greater Glasgow and Clyde (NHSGGC) said: “Our thoughts are with the family and friends of Ms McGregor as they continue to mourn her death.
“A Significant Adverse Event Review (SAER) is under way into the circumstances surrounding Ms McGregor’s death.
“We met earlier this year with her family to apologise for the delay in the post-mortem examination taking place and issues around her death registration.
“We will contact the family when the SAER is concluded and offer to meet with them to explain its findings.”
The case has emerged with NHSGGC health board officials already under extreme pressure for their handling of deaths linked to water infection issues at the Glasgow hospital.
Scottish Labour leader Anas Sarwar has consistently called for the health board’s senior management team to be sacked as a result of the ongoing scandal at QEUH.
Former Scottish Government adviser Andrew Slorance and ten-year-old Milly Main have been among patients who have died from waterborne infections linked to treatment at the hospital.