Europe and Japan are in the midst of one and the U.S. phased out theirs last year. Yet for all the money that has been pumped into major economies, the impact of monetary stimulus remains far from clear.
Richard Koo, chief economist at the Nomura Research Institute, told CNBC on Tuesday that he believed quantitative easing (QE) could cause more harm than good.
Koo said that after the financial crisis, the world's private sector had focused on paying down debt, despite the monetary stimulus aimed at encouraging firms to borrow and invest to help kick start economic growth.
"If the private sector as a group in the West is paying down debt there's no way a central bank injection of liquidity will actually enter the real economy because the private sector is not taking the money," Koo said.
He added that only once the private sector finished repairing balance sheets would it start to borrow again.