[header] How to lose 100 lbs or more as a teen [title] Talk to your doctor. [step] Anytime you're interested in losing large quantities of weight (more than 25 or 30 pounds) you should always consult your physician first. It's important to get a parent or guardian to help make your doctor's appointment and ask what's safe if there are additional resources and support. 
[substeps] Make an appointment with your doctor or pediatrician if you still see one. Talk to them about your desired amount of weight loss and ask how you can go about weight loss safely and appropriately.