A doctor found guilty of misconduct will not be prosecuted for gross negligence manslaughter, the Crown Prosecution Service (CPS) has ruled.
Dr Jane Barton prescribed "potentially hazardous" levels of drugs to patients who later died at Hampshire's Gosport War Memorial Hospital in the 1990s.
The CPS said there was "insufficient evidence" for a prosecution, but relatives have criticised its ruling.
A General Medical Council panel found her guilty but did not strike her off.
A jury inquest held last year into the deaths of 10 Gosport War Memorial Hospital patients found drugs to be a factor in five cases.
Judicial review call
Anne Reeves' mother Elsie Devine, 88, was among those five cases.
She was admitted to the hospital with confusion and kidney problems, was given doses of diamorphine and Midazolam despite there being no record of her suffering pain, and then a tranquiliser.
The inquest found the use of painkillers had been inappropriate for her condition.
Ms Reeves told BBC News: "It has taken 16 months for the CPS to deliberate on this.
"We will be challenging [its] decision. We will be pushing for a public inquiry."
In March, the Council for Healthcare Regulatory Excellence (CHRE) said Dr Barton should have been struck off the medical register, echoing the stance of the patients' relatives.
Dr Barton, who has since resigned, was found guilty of a series of failings in her care of 12 patients who were treated at the hospital between 1996 and 1999.
The GP had told the GMC fitness to practise panel she had had to work under "unreasonable pressure" with an "excessive and increasing burden" in caring for patients.
She was allowed to continue to practise but had 11 conditions placed upon her work, including a ban on injecting opiates for three years.