Knowing the difference between normal teenage behavior and signs of mental illness can be difficult. If your teen is being moody or acting out, you may assume it's because of the physical, hormonal and social changes he or she is experiencing through puberty. Teenagers experience a variety of difficulties and pressures that can overwhelm them.

Know that it is normal for teens to be short-tempered toward their parents and separate themselves from their parents. But if your teen is involved in unhealthy social groups or isolates themselves from you, this may be a red flag that something deeper is going on. Here are some warning signs of mental illness in teens:

Depression

While your teen may go through some hard times, clinical depression is another story. Keep an eye out for:

• Excessive isolation

• Unexpected crying

• Low self-esteem

• Sleeping too much or too little

• Self-harm

• Sudden weight gain or loss

If your teen is exhibiting these signs, you should immediately talk to a professional to see if he or she has major depressive disorder.

Eating disorders

As your teen goes through physical changes and feels social pressure, he or she may develop body-image concerns. These may result in severely unhealthy obsessions. There are two common eating disorders that affect teens:

Anorexia

avoiding food or exercising too much, resulting in extreme weight loss

If you notice your teen is not interested in eating and is getting thinner, he or she may have anorexia.

Bulimia

forced vomiting after eating, characterized by significant weight loss without a change in eating habits

If your teen makes sudden trips to the bathroom after a meal, this may be a sign he or she has bulimia.

These conditions can seriously affect your adolescent's health.

Substance abuse

Problems with mental health may result in self-medication with alcohol or drugs. You should be aware of physical and behavioral signs of substance abuse, such as hangovers, slurred speech and any suspicious paraphernalia. Watch for any prescription drug misuse. If you have any prescription medications in your home, especially Xanax or Vicodin, make sure you keep them out of reach.

General red flags

Aside from the specific symptoms mentioned above, there are some common warning signs of mental illness in adolescents, including:

• Loss of interest in favorite activities

• Excessive sleeping

• Unexpected worsening of academic performance

• Dramatic personality shifts such as excessive anger or aggressiveness

All of these things may indicate your teen is struggling with some sort of mental illness or substance abuse problem.

What you can do to help

It can be difficult to be the parent of a teen going through a lot of transitions, but you can help your teen by being attentive to his or her behavior and keeping communication open. Watch for any abrupt behavioral changes and talk to your child about anything that's going on.

Let your child know that he or she can come to you with anything. Be open about your own struggles when you were a teen. Reassure your child that you care and that he or she is not alone.

And, of course, remember that mental health disorders can be treated. Talk to your teen's pediatrician about any concerns you have to receive a diagnosis and learn about treatment options such as medication and therapy.