Christine Pratt was found dead at her home in Ivy Avenue, South Shore, in January this year.
A coroner’s court heard that Miss Pratt had intermittently struggled with an addiction to the prescription drug codeine.
After suffering two broken ankles in 2013 she was prescribed morphine for the pain.
Miss Pratt’s sister Carole Everitt, 55, told the hearing in Blackpool that she had spoken to her sister the day before her death and that she “seemed fine”.
Ms Everitt said: “Before Christmas we had a few little arguments because she was asking me for co-codamol tablets (which contain codeine) and I had refused.”
In a statement to the court, Miss Pratt’s GP confirmed that at the time of her death, Ms Pratt had been undertaking a reducing regime of morphine sulphate tablets.
It added that at times Miss Pratt had complained of pain from her ankle injury and was prescribed the tablets once more.
Consultant pathologist Sameer Shaktawat said a toxicity report showed Ms Pratt had 10 times the therapeutic dose of diazepam and four times the normal level of morphine in her system.
There were also normal levels of the anti-depressant fluoxetine and sleeping pill zopiclone.
Dr Shaktawat said: “The medication involved is complex when combined and at high levels would cause respiratory failure.”
Police were called when a pharmacy delivery driver got no answer at Ms Pratt’s home and saw her through a window slumped on a sofa.
Coroner Alan Wilson concluded that there had been no third-party involvement and no indication that Ms Pratt had intended to take her own life.
Her sister Carole Everitt added: “It’s very sad. She had an addiction to co-codamol and painkillers.
“She was very popular and enjoyed a career as a nurse in both hospitals and nursing homes, but since she gave up her job she had struggled.
“She couldn’t have children and lived for her greyhounds, we have had a greyhound carved on her headstone.
“She was a real character and lived in Blackpool all her life.
“She will be sadly missed by everyone who knew her.”
The coroner recorded a verdict of death due to drug-related causes.