What is the upper limit for the number of times i can take plan b pill without being affected by side effects? are the side effects harmful?

Plan B: Plan b can be taken whenever you need it. Use as directed. These are basically just oral contraceptive type tablets, which women have taken for many years with acceptable risks. Using as directed has far less risks than regular daily use, but it is still possible that you could have the side-effects of oral contraceptives. Most common side effect is nausea and upset stomach.

You could have side : effects with one use. Don't use instead of regular contraception. Potential SE’s w emergency contraception: tender breasts; changes in menstrual flow (spotting, bleeding, early or late period or spotting instead of period); loose stools; dizziness; headache; nausea/ vomiting; abdominal discomfort or feeling tired.