system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do antidepressants have the opposite effect in young people?

I keep hearing the disclaimers at the ends of antidepressant commercials about how they can increase thoughts of suicide in teenagers. Why don't they work the same in everyone regardless of age? The mechanism is the same no matter what, right?
gpt
Here is the problem with younger people who are taking anti-depressants for the first time.  Younger people are kind of impulsive. They will do things that older people would usually think through. Imagine being depressed for awhile and having low energy. Imagine feeling worthless and guilty most of the time. 

Suddenly, you get this medication that gives you more energy and allows you to think more clearly. Some of the things you may think more clearly about is suicide. The feelings of guilt and worthlessness don't go away very quickly. There is finally energy to attempt suicide, and you are impulsive enough to not put a lot of thought into it. 

Older people who have a bit of maturity will talk to their doctor if they have increased thoughts of suicide. A teen may decide that is the best thing to do.