Iran Press/ America: Donald Trump told the Washington Examiner he had noticed a sudden improvement in Biden's performance in the Democratic TV debates.
The US president offered no evidence his rival might be on drugs other than to say: "I'm pretty good at this stuff," BBC reported.
Biden and Trump will have three debates before the 3 November election.
Back in 2016, Trump suggested his then-Democratic rival, Hillary Clinton, had been 'getting pumped up' before their debates and challenged her to take a drug test ahead of their final live TV encounter. The Clinton camp brushed aside his challenge.
On Wednesday, the president - who is set to deliver his keynote address to the ongoing Republican party convention on Thursday - made a similar claim, arguing that Biden's debating ability had improved markedly in the final debate. 104/207
Read more:
Ex-Trump administration official endorses Joe Biden
Biden leads in latest election poll ahead of party conventions
