Mast cells. Mast cells and basophils are generally thought to be the major sources of histamine and can themselves be modulated by histamine as they express H 1, H 2 and H 4 receptors, although how this varies between different mast-cell types is not yet clear.
3. The pill is to be taken soon after unprotected sex. It should be taken preferably within 24 hours and before 72 hours or else the pill may turn useless. 4. I-pill checks pregnancy by preventing ovulation or fertilisation or implantation of the fertilised egg. 5. I-pill is 95 per cent effective if taken in time.
Research suggests that though it is recommended that you take it within 72 hours after sex, it is moderately effective up to 120 hours (or five days) after sex. However, even though it's referred to as the morning after pill, you don't have to wait for the sun to come up. The sooner it is taken, the more effective it is. Emergency contraception (EC) isn't to be confused with RU-486 (mifepristone), a pill that causes medical abortion in pregnant women within 49 days from the first day of their last menstrual period.