Lydia Post pill is an emergency contraceptive pill that is swallowed after sex to prevent pregnancy, It usually works up to 72 hours after sex. Ingredients : povidone k-25, polacrilin potassium, ethyl cellulose, maize starch, magnesium stearate, opadry white, and lactose Possible side effects Feeling sick (nausea) You might have some irregular bleeding until your next period You might have lower abdominal pain Tiredness Headache