Drugs made a woman act "like a zombie", an inquest heard.
Sharron Impett, 39, of Colebrook Road, Littlehampton, was found dead at her home on December 18 last year.
She had taken a lethal dose of heroin and could not be revived by an ambulance crew.
Coroner Roger Stone ruled the cause of death was dependence on drugs.
In a written statement, Detective Sergeant Julie Buchan said Miss Impett had been living with Brian Kirby, 31, at the time of her death.
Ms Buchan said: "At times in her life, she became very depressed resulting in her resorting to taking drugs.
"She was known to her family as regularly injecting drugs.
"She was prescribed drugs and her sister knew she was abusing these.
"It left Sharron acting like a zombie."
Ms Buchan said Miss Impett and Mr Kirby had gone to The Wick pub in Littlehampton on December 18 and had spent the afternoon drinking.
They left the pub and bought £20 worth of heroine from a nearby dealer.
Ms Buchan said: "Mr Kirby injected himself in the foot.
"He felt the drugs go through his veins and believed the drugs to be stronger than usual.
"He told Sharron to do half a syringe at a time to see how she managed it.
"He then went off to sleep and, when he came round, he found Sharron on the floor face down."
An ambulance was called but she was not breathing and could not be resuscitated.
Pathologist Dr Keith Roberts said Miss Impett died from a heroin overdose which was made worse by alcohol and valium.
Mr Stone said: "This level of drugs came by applying heroin by means of injection.
"There is no evidence to indicate she was other than a voluntary user.
"If only people realised the risks they take in using these substances."
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article