What are the effects of using pills at the time of sex?

I presume that you are referring to the oral contraceptive pill. If you are talking about the oral contraceptive pill then you should know that it will only work if you consume the entire dose which is for a period of 4 weeks. If this is the pill you are referring to then its effect during sex would be to stop you from getting pregnant. If you are sexually active and missed 3 pills, use condoms, or do not have sex until you have taken pills for 7 days in a row.