Peaches Geldof died of a heroin overdose, a coroner has ruled.
The TV presenter had been a heroin addict and took the substitute drug methadone for two-and-a-half years before her death, the inquest heard.
A police search found 6.9g of heroin in her house but there was no indication she had planned to take her own life.
Her husband, musician Tom Cohen, told the hearing in Gravesend the 25-year-old had started using the drug again in February this year.
He had witnessed her flushing drugs she had hidden in their loft down the toilet, but was not aware of any other drugs in the house until they were found by police.
In his evidence, the musician said his wife had taken weekly drugs tests since seeking treatment for her addiction two years ago.
Although she had informed him they were clear, Mr Cohen said he now believed Geldof had been lying about the tests.
Mr Cohen, who married Geldof in 2012, found his wife slumped on the bed at their home in Wrotham in Kent on 7 April after becoming concerned when she failed to answer the phone.
He had been away for the weekend with the elder of their two sons, Astala, leaving Geldof at home with their 11-month old son, Phaedra.
She was pronounced dead at the scene.
After a toxicology report was issued in May, the police launched a criminal inquiry "into the supply of drugs" in connection with her death. No arrests have been made so far.
Det Ch Insp Paul Fotheringham, who led the investigation, said "importation quality" heroin with a purity of 61% - "far exceeding" the 26% purity usually found at street level - was found in a black cloth bag inside a cupboard over a bedroom door.
"The black bag also contained 34 medical syringes, some were with needles and some without, some were sealed in original packaging and some contained traces of a brown coloured residue," he said.
"There were also 45 packaged and sealed syringes, alcohol wipes and cotton buds."
Police also found a pair of knotted black tights under Geldof's body and two other pairs of tights with knots in them elsewhere in the property, along with a number of burnt spoons.
The syringe containing the fatal dose was discovered in a cardboard box next to the bed, which also contained sweets.
Forensic scientist Emma Harris, who had been involved in examining the body, said: "Tolerance to heroin... appears to be lost fairly rapidly when users cease to use the drug, and deaths commonly occur in people who have previously been tolerant and have returned to using heroin."
Pathologist Peter Jerreat said the levels of heroin in Geldof's body were in a "fatal range"; while evidence of codeine, methadone and morphine were also found in her blood.
He further noted that puncture wounds were found on Geldof's body on her elbows, wrists and thumbs.
Geldof's mother, Paula Yates, died of a heroin overdose at the age of 41 when Peaches was 11 years old.
Coroner Roger Hatch said: "It's said that the death of Peaches Geldof-Cohen is history repeating itself but this is not entirely so.
"By November last year she had ceased to take heroin as a result of the considerable treatment and counselling that she had received.
"This was a significant achievement for her but for reasons we will never know prior to her death she returned to taking heroin."
He said her death would be recorded as "drugs related" and expressed his deep sympathy to the Geldof family.
Mr Cohen left the inquest without comment.