Can I prune forsythia bushes at this time of year?

The large (3 foot) forsythia bushes I planted two months ago have dropped all their flowers (weeks ago) but then sprouted at least a foot and a half of new growth. They are starting to look scraggly and the longer limbs are beginning to sag. It it ok for me to prune them back at this tiime of year? Will it hurt them? I’m hoping they’ll just put new growth energy into the lower reaches of the bush. Do I have to wait to prune?