20 microgram / 24 hoursa synthetic progestagen . hormonal contraception.mechanism of action of levonorgestrelit is a progestin derivative exerts it`s action through nuclear progesterone receptors situated in female genital tract, breast, cns, and pituitary. when the drug binds to progesterone receptors it undergoes dimerisation and attaches to progesterone response element of target genes and regulates transcription through coactivators. it inhibits growth hormone release from pituitary by reinforcement of normal feedback inhibition. it reduces frequency of lh secretary pulses, attenuate lh surge, and suppresses ovulation. it causes thickening of cervical mucous and induces sloughing of the endometrium. it also disrupts fertilization and inhibits implantation.indications for levonorgestrel1. emergency contraception 2. long term prevention of pregnancy (up to 5years)