Most diet pills are not approved for people under the age of 18. However, the best thing that you can do is skip taking the pills, concentrate on making your diet healthy and adding in regular cardio exercise.
You don't need diet pills. If you are concerned about your weight, just get a little bit of exercise everyday. It doesn't have to be a lot. Just start off slow and progress. Try a lot of different fruits and vegetables. Find out which ones you like. Pick healthier foods and then eat them in smaller proportions.
No pill will make the weight disappear. You have to change what you eat and move more. Taking diet pills can really hurt you. I know that this isn't what you want to hear but it's the truth. Eat lots of fruits and veggies, and get more exercise.
I know its really hard, but you have to keep in mind what you can get if you do it. Swap out daily nothings, for example instead of eating a hershey kiss, eat some cashews. Instead of eating a BigMac, eat a salad WITHOUT dressing and meat but if you must make it fatfree or light. Instead of getting on facebook, go outside and walk the dog around the block. Instead of eating out, eat at your house. Instead of watching that new episode of your favorite TV show, record it, do the treadmill/elliptical and watch it after. Instead of sitting there during the commercials on TV, try to do some strength exercises (pushups, pullups, plank, weights,etc.).