Austin Bellew, 41, from Llandudno in Conwy county, was found dead in the sea off Hoylake, Wirral, in February 2016.
An initial inquest into his death was halted after his sister said police were "dismissive" of claims her brother had received a death threat.
The assistant coroner recorded an open conclusion.
The inquest resumed in Ruthin on Tuesday and was told a woman had claimed Mr Bellew was strangled over an Â£8,000 drug debt .
Forensic Home Office pathologist, Dr Brian Rodgers, told the hearing he examined the body, but found "no morphological evidence of strangulation".
A post mortem examination revealed several drugs in the body, including morphine from heroin, and cocaine.
Dr Rodgers concluded Mr Bellew had been in the water for about five to six weeks before his body was found.
The inquest also heard from Det Insp Iwan Roberts, of North Wales Police, who said that, during the investigation, officers received "specific intelligence" to "suggest that he may have come to some harm through third party involvement".
However, one of those supplying the intelligence had not witnessed any assault, and her evidence may not have been reliable.
"We haven't been able to identify anyone that can give us factual evidence to support foul play," he added.
The inquest heard Mr Bellew had a long history of drug-taking and crime, and had served time in prison.
In a statement, his sister, Sandra Bellew, described how Mr Bellew told her a drugs debt owed by his brother had been passed to him, and he was in trouble with some "Scousers" over the debt.
North East Wales and Central assistant coroner, Nicola Jones, said there were a "lot of unanswered questions here".
She added: "What I'm going to do is record an open conclusion which means that if any further information comes to light, we come back again."
The cause of death was given as drowning due to morphine and cocaine toxicity.
There are a "lot of unanswered questions" about a drug addict's death but no evidence he died as a result of foul play, an inquest has heard.