I am under weight and i hate it. are there any pills to slowmy metabolism? what can i do to put on weight?

Underweight: I think you should have an evaluation to make sure you do not have any medical condition causing this problem. If not then, you may need to see a good nutritionist.

Etiology: First of all you have to check with your doctor why you're losing weight. Basic blood tests and screening ( according to your age group). Then, if tests are ok, you can make a nutrition plan with a dietician.

Diet and Muscle Mass: To gain weight you have to consume more calories than you are burning. Do this in a healthy way though. Don't choose junk or fast food. Keep a well balanced diet and make sure you are getting all the nutrients you need. Don't cut out exercise as it is very good for you. Weight lifting and other muscle building exercises can help you increase your body mass.

Rule out bad causes: I agree with dr norman. Must first rule out other potentially dangerous reasons why you are underweight, as solving the problem depends on knowing exactly what is causing it.