Is it bad for a teen to binge?

Yes: I assume you are talking about food, but you could be talking about alcohol. Anytime someone binges they are not developing health and responsible behavior and this is especially true for teenagers. Learning healthy habits as a teenager will have long-term positive effects.

Binge: If a teenager is alreay binge drinking that is a serious problem & warrants medical intervention. Consider an addiction medicine specialist.

Our brains & Alcohol: Alcoholism is seen in many families as a common family trait or condition. If a teenager can drink heavily without many consequences then this can be a clue to them and those who care about them that they very well may be on the road to alcoholism. Addiction is a disease that leads humans to despair, disease and death if untreated. Please be frank but supportive to this person to help them stop.