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.
2 doctors agreed: 7 days: Most doctors recommend 7 days of birth control pills before having unprotected intercourse. Even with pills, there is still a 4-6% chance of pregnancy over course of a year. If miss 1 pill, take that pill immediately the next day with that days pill. If miss 2 days pills, take 3 pills and use back up method until you get your period.