A second side-effect is the impact on bank lending and the efficient allocation of resources. Persistently low or negative interest rates and a flattening of the yield curve can damage bank profitability, leading to less capacity to lend. In some countries, there are concerns that low interest rates allow less-productive (zombie) firms to survive.
There are also financial stability risks that can come from low interest rates boosting asset prices (and perhaps borrowing) at a time of weak economic growth. A third side-effect is a possible blurring of the lines between monetary and fiscal policy. If the central bank is buying large amounts of government debt at zero interest rates, this could be seen as money-financed government spending.