Is Plan B safe?

Yes. But is does have potential side effects. Potential side effects w emergency contraception include: menstrual flow changes (spotting, bleeding, early or late period), nausea, vomiting, dizziness, fatigue, headache, breast tenderness & abdominal pain or cramps. Take pregnancy test & notify dr if your period is 7 or > days late. .
Yes. Plan b is safe and effective - it works over 85% of the time if used within 72 hours (3 days) of unprotected sex and about 80% if used within 120 hours (5 days). There are few complications, but there are side effects occasionally, like nausea and headache.