US actress Erin Moran, best known for playing Joanie in 1970s sitcom Happy Days, "likely" died from cancer at age 56, according to a county coroner.
An autopsy reveals that her death was probably due to complications from stage four cancer.
Police say there were no "illegal narcotics found" in her Indiana home.
Moran also starred in the show's spin-off series Joanie Loves Chachi, which began in 1982. She had fallen on hard times in recent years, US media report.
A joint statement by the Harrison County Sheriff's Department and the coroner's office said an autopsy revealed that she "likely succumbed to complications of Stage 4 cancer".
"Standard toxicology tests were performed and the results are pending however no illegal narcotics were found at the residence," the statement continued.
She played Joanie Cunningham, the younger sister of lead character Richie.
Tributes were paid by Happy Days co-stars, including Ron Howard who recalled her "lighting up TV screens".
Moran joined the Happy Days cast in 1974 when she was 13, and made appearances in Murder She Wrote and The Waltons.
In 2010 she was reported to be living in an Indiana trailer park with the mother of her second husband, an employee of Walmart.
She moved there after losing her California home to foreclosure.
In 2010, she joined various Happy Days co-stars in filing a lawsuit against television network CBS, claiming they were owed money from merchandising revenues.
The suit was settled in 2012, with the actors each receiving a payout of $65,000 (£50,000).
They originally asked for $10m.
Moran had been seen outside motels in southern Indiana, after reportedly spending all of her settlement money, and eventually becoming homeless.
Her last listed film credit is for 2010's Not Another B Movie, though she continued to appear on reality television until 2012.