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18 and Under Dr. Perri Klass on family health.

When you have a child off at college, you worry about his general health, state of mind, alcohol use — and, as you sign those tuition checks, academic achievement.

But how much thought do you give to your child’s roommate?

The college roommate relationship has been the focus of research in recent years: Economists and social scientists have used randomly paired roommates to examine “peer effects” and the ways that student behavior may be shaped by the luck of the draw. The studies show that roommate assignments can affect everything from academic performance to freshman weight gain.

Drinking habits can also have an impact. “The bottom line was we found that when you’re matched with a roommate who drinks alcohol, your grades are likely to go down,” said Dan Levy, a senior lecturer in public policy at Harvard and co-author of a 2008 study on college students and alcohol.

When this research was originally published, some parents worried about the dangers posed by “social contagion” in the peer group. But more recent research has provided some surprising — and, for parents, rather reassuring — information about the way that students are affected by the mental illness of a roommate.

In a study published last year, Daniel Eisenberg, an associate professor of health management and policy at the University of Michigan who directs an annual survey of college student mental health, including roommate issues, and his colleagues found no significant “contagion” effect of mental health from one roommate to another.

“Mental health problems don’t seem to be contagious, so to speak, to a large degree between roommates,” Dr. Eisenberg told me. “For example, being assigned to a roommate with depressive symptoms doesn’t increase the likelihood of someone having an increase in their own depressive symptoms.”

Another 2013 study showed that binge drinking was the only “contagious” risky behavior; the others examined by the researchers, like smoking, gambling and sex with multiple partners, were not affected by a roommate’s practices.

But even if mental health problems don’t cross the room like mononucleosis or the flu, plenty of issues — whether smaller distractions or larger moral dilemmas — may be posed by life with a roommate who is struggling.

Imagine you are a college freshman living (at substantial expense to your parents) in a relatively small space with someone who has been assigned to you in the interest of broadening your horizons and building strong peer relationships … or something to that effect.

And you are beginning to feel that something is wrong with your roommate. He seems to have stopped going to class, or participating in extracurricular activities. She’s losing too much weight, and exercising fanatically. He has stopped taking the medication that helped keep him on track through high school. You think she may be cutting herself. You even wonder if she might be suicidal.

“We don’t want roommates feeling they have to handle this on their own,” said Greg Eells, the director of counseling and psychological services at Cornell University. “A college residence hall is not a resident psychiatric ward. Sometimes the appropriate response is professional help.”

And what about parents? As a pediatrician, I have certainly taken the occasional call about a roommate or classmate who is doing something strange, troubling or possibly dangerous, and my role has generally been to say, “Let your roommate know how worried you are, and why, and tell the resident adviser.”

Sometimes students absolutely don’t want to involve the university hierarchy because they’re afraid of getting a friend in trouble. And there has been criticism over the handling of mental health issues on campuses.

A student who feels some connection with a roommate’s parents may be more comfortable going for help to them — yet another reason to know and be known by your child’s roommate, at least a little.

Sometimes a student fears angering the person in the upper bunk. Dr. Janis Whitlock, a research scientist at Cornell and a co-author of the 2013 studies, researches nonsuicidal self-injury; as an expert on a college mental health website, she deals with the concern that a roommate may be cutting herself, advising a worried roommate to get help.

“In a lot of cases it’s a friend, a roommate, a peer, who noticed first and made the choice to tell an adult,” she said. Their roommates often feel anger and resentment about being found out, she added, “but in all cases, they’re grateful in the long run.”

Dr. Eisenberg’s research shows that more than half of college students with significant symptoms of depression, not to mention those who drink heavily, are not getting help. That’s a potential role that roommates and friends can play.

The intimate perspective that a roommate has can be extremely valuable in detecting problems that really put a student in danger. Though a roommate cannot be responsible for treatment, Dr. Eells has seen the bond work powerfully to help students in trouble.

“A roommate conveying a sense of ‘I care about you’ — these social connections can be lifesaving,” he said. “The outcomes can be pretty magic.”