He had arrived at their home with his mother thinking Peaches was asleep.
But at the opening of her inquest in Gravesend, Detective Chief Inspector Paul Fotheringham, of the Kent and Essex Serious Crime Directorate, said a post-mortem examination was inconclusive, prompting further tests.
But he told the hearing: “Recent use of heroin and the levels identified were likely to have played a role in her death.”
The TV presenter and writer Paula Yates, died from an accidental heroin overdose at her London home aged 41 in 2000.
Rolling Stones bassist Bill Wyman, model Kate Moss and Sarah Ferguson, the ex-wife of Prince Andrew, were among the mourners who attended Geldof’s funeral in Davington, Kent, last month.