Some warning signs are obvious—but others are harder to detect or may be mistaken for normal adolescent rebellion.

A new study, presented today at the annual meeting of the Pediatric Academic Societies (PAS) found that drug use, in addition to harming academic performance, may also indicate that teens are facing other serious personal problems.

Parents, teachers, and school officials can help teenagers at risk for trauma, mental health problems, and other serious health risks by staying alert for warning signs. Even substance use on campus, often viewed by school officials as an isolated disciplinary problem, may be an opportunity to help troubled teens.

“We found that students using alcohol or marijuana at school have dramatically increased rates of having experienced trauma and having poor mental health,” said lead author Dr. Rebecca Dudovitz, an assistant professor of pediatrics at Mattel Children’s Hospital UCLA and the UCLA Children’s Discovery and Innovation Institute, in an email to Healthline.

“These are issues that some teens have a hard time communicating to adults and so might go unnoticed by school officials,” Dudovitz added. “That’s why it is so important that students who are found using alcohol or marijuana at school are screened for other health issues and connected urgently to services that can help them.”

Dudovitz and colleagues used data from a 2011 Centers for Disease Control and Prevention survey of more than 15,000 U.S. high-school students.

The survey showed that 9 percent of all students reported using alcohol or marijuana at some point during school. This in-school drug use was associated with an increased risk of other serious health behaviors—including a 64 percent chance of riding in a car with an intoxicated driver, a 46 percent chance of having symptoms of depression, and a 25 percent chance of having attempted suicide. These rates were higher than those for students who used alcohol or marijuana only outside of school and for those who did not use substances.

“Given the potential for these health risks to pose significant danger to teens, and the fact that they might not otherwise come to the attention of a caring adult, when a student is caught using alcohol or marijuana in school, it is a real opportunity to identify at-risk teens and get them help,” said Dudovitz.

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School officials may be more likely to notice changes in a teenager’s behavior, but parents can also stay alert for warning signs of underlying problems.

“If there’s something that your teen is doing that’s clearly very different than what’s average for teens, then that’s something to pay attention to and to look into,” said Dr. Fredrick Matzner, Director of Child Psychiatry at the Wakefield division of Montefiore Medical Center.

While the definition of “normal” behavior is somewhat subjective, parents can look at how their child has changed over time.

“If you have a kid who has a bad temper, but either the temper is getting worse over time or the temper is really severe,” said Matzner, “then that’s a symptom [of a problem].”

Other potential warning signs include not wanting to go to school and difficulty making friends.

“If you have kids who are unable to make friends at all, then that’s different than most kids,” says Matzner. “Most kids, it’s pretty easy for them to make friends. Some are shyer than others, some are more outgoing than others. But if you have no friends, then there’s something going on that’s getting in the way of doing what normal kids would do.”

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But warning signs aren’t always so obvious. A teenager with depression may not appear sad, but could display other behavior that is out of the ordinary.

“One of the classic symptoms of a severe depression is not being able to sleep at night,” said Matzner.

That’s why it is important to look for behavior that doesn’t line up with the child’s past behavior or with what other teenagers are doing.

The next clue is whether the child’s school, social, or home life has started to suffer.

“The second issue is actually pretty straightforward, and as psychiatrist it’s one of the things I look at all the time,” said Matzner. “Has there been a change in how well the teenager is functioning?”

This can manifest in a number of ways, such as a sudden drop in grades, social isolation, or getting into more fights. In particular, drug use can affect school performance, especially when it moves beyond one-time experimentation.

“Smoking marijuana or getting involved in other kinds of drugs is one of the biggest reasons for a sudden drop in the ability to function in school,” said Matzner. “You just can’t pay attention when you’re using, if you’re using a lot.”

Adolescence is a time filled with change for many teenagers, and this phase may make it difficult for parents to identify warning signs.

“There are a lot of symptoms … in terms of feelings and emotions and impulses and behaviors, that all kids go through,” said Matzner, but when it is a problem, “the severity is markedly different from what normal kids go through, or it interferes in their life in a marked way.”

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Matzner offers some advice for parents who notice a red flag.

“I would always talk to the child first,” he said. “And I would sit down with them, and I would talk to them about what they think is going on, and what’s different now from what it was before.”

If the problem involves school—a drop in grades, fighting at school, or skipping class often—parents should talk to the child’s teachers or guidance counselor as well.

“That’s an easy way to get more understanding of whether the problem that the kid is going through is very different than the normal trials and tribulations of adolescence,” said Matzner.

Parents can also seek professional help if their child is doing poorly in a major area—such as getting into fights every day, having no friends, or failing multiple classes. Counseling or other medical help is especially important if the teenager is hurting other people, damaging property, or talking about harming himself or herself.

“If they say anything at all that sounds like they wish they were dead,” says Matzner, “or that they feel like killing themselves—that’s a dangerous thing to hear, and it means that the child really needs to be evaluated right away.”

Threats against themselves—or others—may be told to a friend or posted on Facebook or other social-media sites. Although the teenager may not really intend to hurt himslef or herself, in this case it is best to err on the side of caution.

Many people think of teenagers as being surly or having frequent mood swings, but according to Matzner, it’s not normal for teens to be very unhappy all the time.

“The average teenager has ups and downs, and has times when they get upset, and they misbehave sometimes and break the rules sometimes,” he said, “but on the average, they feel pretty good and function pretty well, and get along pretty well with everybody in the family.”