A man has gone on trial accused of putting a lethal dose of morphine into a four-month-old baby's bottle.

Graham Andrew Wilson, 41, allegedly put morphine into his partner's baby's bottle at the couple's Elizabeth South home in Adelaide in 2007.

Wilson has pleaded not guilty to a charge of criminal neglect and is facing trial before a jury in the District Court.

Prosecutor Jeff Powell said Wilson suffered a workplace accident and had taken a variety of painkillers, including morphine.

He said the mother had put the baby down after the girl drank some of the formula made up by Wilson and noticed the infant seemed to be staring and breathing strangely.

A locum doctor thought the infant had bronchitis and sent her to the Lyell McEwin hospital in northern Adelaide, where blood tests were done.

The baby was then sent to the Women's and Children's Hospital and spent a week on a ventilator, eventually making a full recovery.

Mr Powell said Adelaide's Forensic Science Centre analysed the blood samples and they indicated there was a potentially-lethal concentration of morphine.

He said Wilson was interviewed twice by police.

'Medical impossibility'

The first time he told them the infant liked to lick his arm and may have extracted the morphine from his perspiration.

Mr Powell said evidence presented during the trial would suggest that was a medical impossibility.

The prosecutor said Wilson subsequently told police he had no recollection of the day concerned, due to his consumption of painkillers and that he may have accidentally dropped a capsule of the painkiller into the feeding bottle while he was taking a capsule himself.

Mr Powell said medical evidence would suggest morphine capsules were intended to work by time release, so for the drug to take immediate effect the capsule would have had to have been crushed into the baby's milk formula.

"It is not the prosecution case that he set out to endanger [the baby's] life," he told the court.

"The reality may be as simple as this, that he just wanted to get a good night's sleep and that he did something stupid, so stupid in the extreme that it amounted to criminal neglect."

The trial before Judge David Smith continues.