The euro slid 0.4 per cent against the greenback, after rising as high as US$1.3993 earlier in the session, the highest level in 2-1/2 years.
"Draghi's guidance was the key takeaway from today's press conference," Robert Lynch, a currency strategist at HSBC Holdings in New York, told Bloomberg News. "The more overt signal of the potential - if not the outright intention - to ease policy next month has already worked to drive euro-dollar down after the pair nearly eclipsed the US$1.40 threshold."
Draghi's comments also bolstered the appeal of bonds in the euro zone, pushing yields lower.
Across the Atlantic, equities seesawed through the day. With about an hour of trading left in the day in New York, the Dow Jones Industrial Average rose 0.29 per cent. The Standard & Poor's 500 Index was down 0.01 per cent, while the Nasdaq Composite Index slipped 0.07 per cent.
An early rally in some of the momentum technology stocks faded as the day unfolded.
In testimony to a US Senate panel, Federal Reserve Chairman Janet Yellen said it might take five to eight years for the Fed to unwind its monthly bond purchases. The central bank's balance sheet has widened to more than US$4 trillion from about US$800 billion in 2007.
"We've not decided, and we'll probably wait until we're in the process of normalising policy to decide, just what our long-run balance sheet will be," Yellen said, adding it will be "substantially lower" than it is now, Reuters reported.
"If we do that [stop re-investing funds from expired assets] and nothing more, it would probably take somewhere in the neighbourhood of five to eight years to get it back to pre-crisis levels," according to Yellen.
Gains in shares of AT&T and Walt Disney, last up 1.9 per cent and 1.5 per cent respectively, outweighed declines in shares of Merck and UnitedHealth, last down 1.4 per cent and 1.2 per cent, to keep the Dow in the green.
The latest data showed initial claims for state unemployment benefits fell 26,000 to a seasonally adjusted 319,000 for the week ended May 3.