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.
Most pills you can have sex after a week, but some you have to take them for a month before it's safe. Either way, make sure you take the pill at the same time every day and if you ever miss a pill, make sure you use another form of protection for a week. Source(s): Rose Â· 8 years ago. Thumbs up.