What is the ruling on using birth control pills

Question : The sister calling in with us on the line asks about birth control pills for a woman: Is it permissible for her to take such treatments?

Answer : First, she should not take them except for a pressing need; this is a condition. The second condition is that there be no harm in them, and I say that it is known that there is harm in them. The third condition is that the husband gives permission for this.