I found the following article very scary, especially have a teen with ADHD, it's talking about a recent study of teen suicide:
Nock and his colleagues found that almost all teens who thought about or attempted suicide had a mental disorder, including depression, bipolar disorder, attention deficit hyperactivity disorder (ADHD) or problems with drug or alcohol abuse.
More than half of the youth were already in treatment when they reported suicidal behavior. Nock said that was both "encouraging" and "disturbing."
"We know that a lot of the kids who are at risk and thinking about suicide are getting (treatment)," he told Reuters Health. However, "We don't know how to stop them - we don't have any evidence-based treatments for suicidal behavior."
You can find the complete article at: http://vitals.nbcnews.com/_news/2013/01/09/16434761-1-in-25-us-teens-attempts-suicide-national-study-finds?lite
They stress in the article how important it is to keep the line of communications open with your teen, and to be comfortable talking about depression with them.
The problem is, how do you make sure that your teen is being open about their feelings and emotions, and not just blowing you off?