The dollar ticked lower on Friday as investors, cautiously optimistic about the results of a drug trial and President Donald Trump's plan to reopen the economy, regained some appetite for risk.

Sentiment was boosted overnight by a media report detailing encouraging partial data from experimental drug trials on severely ill COVID-19 patients at a University of Chicago hospital.

News of Trump's plans to reopen the world's largest economy was also taken by investors as a positive sign, even after Thursday's jobless data showed a record 22 million Americans sought unemployment benefits in the last month.

The overnight moves toppled the dollar, which has closely tracked risk sentiment through the coronavirus crisis, from a week high, with the dollar index last down 0.16%. Other safe-haven assets like Treasury yields were lower, while the S&P 500 index rallied 1.3%.

The dollar also fell against the euro, the British pound and the Canadian dollar, though it strengthened against the Japanese yen and the Swiss franc , other safe-haven currencies. "Stronger risk appetite put a brake on the greenback's rally," said Joe Manimbo, senior market analyst at Western Union Business Solutions.

As the dollar fell, the euro rose 0.41%. The euro has fallen about 1.36% against the dollar already this month, facing its biggest monthly fall since July last year, after hitting its lowest against the Swiss franc in almost five years earlier this week.