The family of a Somerset pensioner who died after being given a wrong drug dose has lodged a formal complaint with a pharmacy.
Ellen Newman, 81, was given a double dose of Primidone to control tremors after a Boots dispenser gave incorrect information to her care home.
She became ill and was taken to Weston General Hospital where she later died.
A statement from Boots said the company was co-operating fully with the coroner's inquiry.
Mrs Newman was a resident at Earlfield Lodge residential home in Weston-super-Mare when a hospital doctor prescribed her half a tablet a day of Primidone.
As care homes are legally not allowed to halve tablets, the pills were returned to the pharmacy.
Later that day, the tablets were sent back to the home with instructions from the pharmacist that it was safe to give a whole tablet.
The care home's medical records on Mrs Newman said: "Ellen became very drowsy and drunk-like after an hour of having the tablet."
The next day, it was said that Mrs Newman refused any food and wanted to go back to bed.
Within four days she was admitted to Weston General Hospital with kidney and liver failure. She died the next day on 23 June.
In correspondence sent to the nursing home, Boots said a trainee dispenser rang up the family doctor, spoke to a receptionist at the surgery and was told it was all right to give one tablet twice a day - quadruple the dose originally recommended.
After taking the first tablet - a double dose - Mrs Newman did not take more.
Mrs Newman's daughter Vanessa is taking preliminary legal action to find out how the mistake happened.
She said: "It wasn't until the hospital rang us and said, 'there is nothing we can do', that we realised we were going to watch Mum die.
"It was very upsetting. I think it's disgusting. It shouldn't have been allowed to happen and it could happen to other people."
Boots said in a statement: "We take patient safety very seriously and are co-operating fully with the coroner's enquiries.
"As a date for an inquest has not yet been fixed we are unable to comment any further at this time."
Lawyer Gillian Tayler, who is representing Mrs Newman's family, said they had learned that after an internal investigation, Boots had made a number of staffing changes and was making sure dispensers had "more reflection time" to consider prescription requests.
She said the family wanted to find out whether over-medication was in any way responsible for Mrs Newman's death.
She added: "We are still waiting for a date for an inquest but in the interim, the family has lodged a formal complaint with Boots.
"The family clearly have concerns due to the fact that Mrs Newman rapidly deteriorated from being given the medication."
A date for Mrs Newman's inquest has yet to be set.