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.
However, recent research indicates that both doses can be taken at the same time up to 120 hours after unprotected sex. The pills are more effective the sooner they are taken, so take 2 Plan B pills at the same time as soon as possible after unprotected intercourse. Plan B has been replaced by the one-pill product Plan B One-Step. Facts about Plan B: Plan B is a way to prevent pregnancy AFTER unprotected sex.