Any hormonal medication that you take (for example, the Birth Control Pill or Depo provera) to help you avoid pregnancy overrides your bodies natural hormonal system.
This means that for the time you are using these medications, the medication runs your menstrual cycle and fertility not your body.
When you stop taking the medication it takes some time for your body to regain its natural menstrual cycle. How long it takes to do that depends on:
If you are trying to conceive and have been on the Pill or others, you cannot necessarily assume that you will fall pregnant straight away. It takes time for the artificial hormones to be released from your body and for your body to get back into the swing of running its own menstrual cycle and fertility again.
You should allow at least 3-6 months to get the Pill out of your system. If you are older (over 30 years) or have been on the medication for over 3-5 years then you may need to allow 12 months to resume a natural cycle.
Remember that a healthy regular cycle represents a healthy fertility system which is far more likely to have a healthy pregnancy and carry a baby to full term. Keep this in mind if you are tempted to hurry the process along.
There are things you can do to speed up the coming off medication process see the next few chapters on incresing the odds.