A woman has admitted the manslaughter of her husband by administering a morphine dose after a period in prison reduced his tolerance to the drug.

Mark Fenton Campbell died at the couple's home in Peterborough Street, central Christchurch, on June 26 last year.

His wife Kimberley Anne Campbell, 27, today pleaded guilty to the manslaughter charge before a depositions hearing was due to begin in the Christchurch District Court.

She was remanded for sentencing in the High Court on July 2. A pre-sentence report was ordered, with an assessment of her suitability for home detention.

She was granted bail to live at a Lower Hutt address, report weekly to the police, and to abstain from the use of illicit drugs.

Defence counsel David Ruth said Campbell had been abiding by the reporting conditions. He understood the drug ban "has been complied with, to the letter".

The police summary of facts said the couple met in 2002 and married. Kimberley Campbell was a morphine user and introduced her husband to the drug.

She would process morphine sulphate into heroin and inject it.

Sometimes, when he was too cold to find his own veins, her husband would get her to inject him with the heroin.

By mid-2005, the couple were each injecting 60mg a day in a single dose. Mark Campbell had a high tolerance but knew how much he could take safely.

In December 2005 he was imprisoned. Kimberley Campbell visited him only about four times while he was in jail, but stayed in touch weekly by letter and phone.

He was released on June 25, 2008. About 3pm that day, the woman bought two 60mg morphine tablets and another chemical for processing it, for $120 at an unknown address.

She then processed the drug into heroin. Her husband asked her to make up two 30mg syringes so that he could take one straight away and the other one later in the evening.

She injected 60mg into herself, and injected one 30mg dose into her husband.

The defendant told the victim that she did not want him taking the second syringe to (another house) and proceeded to inject the second dose of 30mg into the victim's arm within five minutes of the first dose.

They returned to their home in Peterborough Street where Mark Campbell went to sleep. At 11pm the woman found he was not breathing and spent 40min texting her sister before calling an ambulance.

Ambulance officers found the husband dead, and a post mortem showed he had died of a severe pulmonary oedema from morphine overdose.

Kimberley Campbell blamed herself for the death but said she believed he would have injected the drug elsewhere himself if she had not done it.

She accepted that her husband had wanted two half-doses of the drug with time in between because of his reduced tolerance.

After the guilty plea, the police withdrew a charge of manufacturing heroin.