Q. DID YOU EVER SMOKE POT? A. IT'S COMPLICATED.

Many years ago, when I was a resident in pediatrics, an adolescent
patient asked me if I had ever smoked pot. It wasn't a friendly
question, more an oh-yeah-says-you response to my own inquiries,
warning me off.

No patient has asked me that for decades. But recently, I have found
myself in several all-pediatrician conversations about the topic.

Doctors, and the parents who look to them for advice, need a way to
integrate their standards of honesty with what we know about
preventing substance abuse -- and with new research that makes it
clear we know a lot more today than anyone did when we were young.
(Which may help explain some of the dumb decisions made by so many of
us, including me.)

In particular, scientists understand much more about the neurobiology
of the teenage brain and the risks of experimenting with drugs and
alcohol during adolescence. While we used to think the brain was
relatively mature by 16 or 18, in fact it is still developing into the
mid-20s.

What does develop early is the pleasure-seeking area, the nucleus
accumbens. The regions that help with abstract thinking, decision-
making and judgment are still maturing, and therefore less likely to
inhibit the pleasure-seeking behavior. So drugs and alcohol can
actually lead to permanent changes in the way the brain works -- in
particular, many experts think, a greater likelihood of addiction in
adulthood.

But giving sage advice to the young has never been a simple task, and
when a parent's own history is brought up, it gets even more
complicated.

There's a moral question, for grown-ups who pride themselves on
honesty and openness. There's a fear that no matter how carefully you
spell out the lesson of your own story, you may be offering your child
an implicit lesson about the lack of consequences, a kind of I-
did-it-and-I'm-fine parable.

And there's a common parental anxiety about losing the moral high
ground, a fear that someday this will be thrown back in your face.
That can be especially troubling in more fraught situations, when
children or parents (or both) are dealing with drug and alcohol problems.

"That comes up all the time when I'm counseling parents," said Dr.
Sharon Levy, director of the adolescent substance abuse program at
Children's Hospital Boston. "They say, 'Well, what should I tell her
- -- or not?' "The research on this point is limited. But there is
evidence to suggest that when parents provide more information and
better modeling early on, their children's risk of substance abuse
goes down. And a 2009 study by the Hazelden addiction treatment center
in Minnesota found evidence that many teenagers believed that parental
honesty about alcohol use was a positive influence.

Of course, every parent, every child and every situation is different,
and there is no fixed rule that says parents and doctors need to offer
any particular information about their drug or alcohol use, past or
present.

Instead, it's important to figure out "why are you asking, what's
going on around you?" said Dr. Janet F. Williams, professor of
pediatrics at the University of Texas Health Science Center at San
Antonio and head of the American Academy of Pediatrics' committee on
substance abuse.

"What you think they want to know may not be at all why they're
asking," she said. And as with other important conversations, take
account of the child's developmental stage; you answer a question from
a 12-year-old and a 22-year-old in different terms and in different
detail.

You don't need to tell everything. But if you decide to answer, don't
lie. "Tell them without glorifying it," Dr. Levy said, "and if you
think you made a mistake, tell them that too."

In fact, a child who asks a parent this question may be worrying over
how and when to bring it up. Don't assume that the agonizing and the
self-consciousness are all on your conflicted, guilty parental side.

Treat the question with respect, and use it, as the experts would say,
to keep the conversation going. It may not be a question you
particularly want to be asked, but it's a larger conversation that as
parents, we know we need to encourage. (Two useful Web sites are
teens.drugabuse.gov, which has information geared to adolescents; and
teen-safe.org, which offers advice on talking with teenagers.)

What about that familiar parental nightmare, the angry adolescent who
reacts to discipline or reproof by turning it around on you with an
accusation about your own transgressions? Deborah R. Simkin, a
psychiatrist who is a liaison to Dr. Williams's committee from the
American Academy of Child and Adolescent Psychiatry, drew an analogy
to an alcoholic who resists treatment by trying to bring up other
people's issues.

"The kid's trying to divert the attention from an appropriate
intervention by a parent," she said. In such cases, the parent's
response should be clear: "We're not going to discuss what I did,
we're going to discuss what you did."

What we want to do as parents is transmit wisdom -- even if we
acquired it the hard way -- without our children's having to take
risks. "So you drove without a seat belt and you didn't die in a car
accident, does that mean you want your kid driving without a seat
belt?" Dr. Levy asked. Or as Dr. Williams put it:

"If the way it's presented is, 'This is risky, and I hope that you
don't have to touch the hot stove to find out you get burned,' they
don't have to take the same chance."

And finally, after all the cautions and the anxieties, it's essential
to come back to the positives -- "always remembering to notice the
good about your child," Dr. Williams said.

After all, the most important message a parent can give is not about
the mistakes that can derail a child, but about the joys of finding
your way.

Tell your child, in Dr. Simkin's words, that "I would prefer you to
work on finding your passion, finding what in life you want to do" --
and celebrate that potential.

And for that very reason, Dr. Williams said, "I would like them to
have every brain cell they can have.