Dear Dr. K: My teenage son seems different lately. He’s lost interest in team sports, is more secretive and is hanging with a new crowd. I’m worried he may be abusing drugs or alcohol. I keep trying, but he won’t really talk to me about it. What can I do?

Dear Reader: Few things are more important to teenagers than being part of a group of their peers. It appears to be hard-wired in us: Teenagers in many different cultures tend to band together and to suffer if they are not part of a group. When the group does drugs, they can be hard to resist.

Teens are surrounded by images of alcohol and other drugs. They see them in movies and on television. They hear about drugs and alcohol in song lyrics. Alcohol ads show drinkers as popular, beautiful, rich or often all three.

It’s common for teenagers to try alcohol or drugs. Why? Some teenagers use alcohol or drugs to feel good. Some do it to relax or to fit in with their peers. Some do it to make themselves feel older or more sophisticated. Some are just plain curious, and since they are teenagers, consider themselves immortal. They ask themselves, “How harmful can it be?”

You might feel that the last thing your son wants is your advice. The same “wiring” that makes teens vulnerable to peer pressure seems to make them resist parental advice.

Still, talk to him – just don’t come down too heavy. Make an argument, not a judgment. It might not seem like he’s listening to you, but he probably hears everything you’re saying. More important, he knows that you care.

Make sure your son understands that drinking or taking drugs can affect his future. It could ruin his chances of getting into college or getting a job after graduation. It can lead to addiction – and possibly death.

I would suggest asking your son directly if he is involved with drugs or alcohol. If your teen tells you he isn’t, but you still are concerned, talk with his pediatrician or school guidance counselor for advice.

It’s also important to set a good example – that’s how kids learn.

Dr. Anthony Komaroff is a physician and a professor at Harvard Medical School. To ask a question or for more information, go to askdoctork.com.