How can you tell if someone has a mental illness?

You can't just look at someone and tell. In fact, many researchers have difficulty diagnosing mental diseases in teenagers because their brains are still developing and there aren't any definitive tests for mental illness.

Strange behaviors may be a result of many factors, including hormone levels, normal brain changes, everyday stresses or even extraordinary circumstances like your parents divorcing, someone close to you dying or other life-altering events.

The coolest kid in the room could be afflicted with depression or bipolar illness. The student who seems a little weird... well he may be having a bad day or he might be the next Bill Gates.

Mental illness is diagnosed by looking for a pattern of behavior. Evaluating mental illness isn't easy and should be left to professionals.

So what's normal?

Normal is a pretty slippery concept. Mostly it's a matter of degree of how you're feeling. It's completely normal to feel a little unsure of yourself, awkward and shy and not sure where you fit in. But it could be a problem if you totally hate yourself, feel really guilty all the time - like everything that goes wrong in the world is somehow your fault - or just feel like you're worthless.

Everyone gets upset sometimes. It's normal to feel down and sad for a day or so when you have a fight with a friend or family member or are having a hard time at school. But if you feel like you can't get out of bed because you're being sucked into a black hole of despair or feel like everything in the world is futile and dark cloud hangs over you, you could have depression. Even if things haven't gotten that bad, but you feel hopeless and helpless and sad, a mood you just can't shake, it might not hurt to talk to someone.

Teenagers sometimes disagree with their parents. That's normal. It's really not normal to hate your parents and be angry with them all the time or consistently go into a rage over nothing. Some parents may deserve anger - if they are abusive or neglectful - but that's something you should be seeking help for, too. It's not your fault, but it will be much better for your physical and mental health if you get support.

Despite what parents, teachers and other concerned adults might wish, teenagers do tend to experiment with sex, drugs and alcohol. It's really not good for you, but it is normal behavior. What's not normal is to need alcohol or other drugs to feel good or to only have casual sex.

It's normal to want to have your own life and make up your own mind about stuff. But it's extreme to completely shun your friends and family and withdraw from society. It's OK to feel a bit antisocial once in a while and want to spend some time by yourself, but it's not healthy to never form friendships and shut yourself away all the time.

People's tastes and interest change as they get older, but if things that used to make you happy bring no joy and you just can't get into anything any more or if your feelings seem to be shutting down so that you feel nothing, that could be a warning sign of trouble.

It's absolutely normal to explore your identity and try out different hairstyles, clothes and jewelry. The kid who dresses completely in black and has lots of piercings isn't necessarily depressed. He or she may just be trying out a different identity to see if it fits, or trying to hide some physical flaw, or maybe has trouble matching colors and thinks black is easier. But kids who have lost all regard for personal hygiene and don't care about how they look at all and have other odd behaviors could be having a problem that needs addressing.

Finding your school work more challenging is normal. Suddenly having problems concentrating, finding your thoughts racing, and seeing your grades plummet as a result isn't.

Sometimes teens try things that aren't always wise. It can be a thrill, but if you're always having this incredible urge to do something really dangerous or you're completely unable to control your impulses, that might be a cause for concern.

And it's definitely not normal to want to hurt yourself or others or kill yourself. If you're having those thoughts or if you're cutting or hurting yourself to try and relieve your other pain, please, ask for help immediately.

If I'm feeling blue and I get angry a lot, does that mean I might have mental illness?

Not necessarily. It's normal to go through periods when you are less than your best. But you shouldn't be feeling consistently angry or sad day in and day out. If you do, it's important to let someone know how you are feeling.

The first people you should turn to are your parents. But if that's difficult, seek out a counselor at school or a favorite teacher. Sometimes this is easier said than done, because when you are feeling low it seems futile to ask for help. Try to remember that it's the best first step you can take.

Look, if you're worried, go get checked out. You could find yourself being completely relieved to know that you're an absolutely normal kid.

But if I talk about my issues will that mean someone will put me on drugs or I'll get locked up in some kind of psych ward?

No. Psychiatric wards are a last resort. Hospital stays are pretty much reserved for people who are in danger of hurting themselves or others.

Most kids who have concerns do talk therapy. That may sound useless, just sitting around talking about your problems, but really, therapy helps break negative thought cycles and helps people direct their brain in healthier directions.

Everything you do changes your brain a little. Therapy can help make sure that change is in a positive direction, rather than adding to the negative spiral.

If you have an illness that's due to a chemical problem in your brain, drugs may help. Again, it's a way to restore balance to your brain and get its development moving in the right direction.

If you are prescribed drugs, you should be monitored and also get therapy. Lots of studies show the combination is more effective than drugs alone.

No one even needs to know you asked for help if you don't want them to. Professional counselors don't talk about their patients and won't reveal your identity. They can't. By law, doctors, schools and other counselors must keep health information - including mental health information - confidential. So you don't have to fear being labeled as someone with a problem.

What if a friend tells me he or she is considering suicide?

Take this very seriously. Many people over the course of a lifetime will think about suicide. But people who talk about it with others are somewhat more likely to take action. You should encourage that person to share this information with a responsible adult.

-----Tina Hesman and Richard H. Weiss