What to do if i don't have add and i only weigh 130lbs. is it ok for me to take this much to help me study?

Never: You should not take any medication to "help " you study. Unless prescribed by a reputable , trained professional. Medications have side effects, sometimes very serious ones.Bad, bad idea.

This much of what?: Even though you haven't said what specific medication or how much you're considering taking, it's both dangerous and illegal to take controlled substances that have not been prescribed for you. (many add medicines are controlled substances.) add medicines won't t help you study if you don't have add -- but they could give you experience of associated side effects.