You can probably remember some morning you struggled to get out of bed. Maybe you kept thinking about the exam you failed, the party you were not invited to or the job you didn't get. If you are clinically depressed, every day is like this—but worse. Nothing you used to enjoy is fun anymore, and you lack the will to do what it takes—to exercise, say, or reach out to a loved one—to pull yourself out of your gloom.

Depression is the leading cause of disability worldwide, according to the World Health Organization. About 20 percent of people worldwide will experience it during their lifetime. This risk is highest for women, young adults and those living in disadvantaged communities or developing countries. If you let down your boss or your child because your misery overwhelms you, depression spreads outward to others and affects society.

Treating depression is tricky. Antidepressant medications have side effects such as drowsiness, sexual dysfunction and weight gain that cause many patients to stop taking them. Nearly one third of patients do not respond to their initial treatment, and of those who do find relief, four out of five will become depressed again later. On average, people relapse about four times across the course of their life.

New strategies for treating the illness are desperately needed, especially in places where medication and psychotherapy may be unaffordable or unavailable. Accumulating evidence now supports a simple, inexpensive approach that may fill a large part of the treatment gap. Our data and those of others show that joining a group, or several groups, can both prevent and cure depression. The type of group is irrelevant as long as it matters to you. It must become an integral part of who you are.

The Ache of Isolation

The American Psychiatric Association recommends two kinds of first-line treatments for most cases of depression: antidepressant medication and psychotherapy. Both therapies can work quite effectively, either by changing brain chemistry or by altering one's perspective on life events. Both rest on the assumption that depression is a problem within an individual. Yet evidence suggests that the disorder has potent external triggers. In particular, 60 to 90 percent of people who become depressed have recently suffered some kind of loss—of a job, friendship or romance, for example. In addition, depression preferentially strikes those who live alone. And in recent years researchers have discovered that a sense of social isolation, often arising when you stop participating in activities you used to enjoy, augurs depression within a year. In a study of 229 middle-aged and older adults published in 2010, social neuroscientist John T. Cacioppo of the University of Chicago and his colleagues found that individuals who reported being lonely at some point over a five-year period were far more likely to develop depression symptoms a year later than were those who scored low on a measure of loneliness, independent of age, gender and initial depression severity.

In fact, loneliness often precedes the most devastating consequence of depression—suicide. In a study published in 2012 psychologist Tonelle Handley, then at the University of Newcastle in Australia, and her colleagues investigated various longitudinal predictors of suicidal thoughts—including psychological factors, family, social networks and availability of social support—in 1,356 people living in rural New South Wales. The researchers found that those with the lowest level of social support were the most likely to be thinking about killing themselves one year later.

The Social Cure

The more we learn about depression, the more social isolation seems to be a key factor in its expression. Interactions with others, then, might logically guard against the illness. Such contact works only when a person develops a sense of belonging, however. In another study from 2012 social psychologist Fabio Sani of the University of Dundee in Scotland and his colleagues surveyed 194 adults about how much they saw and spoke to members of their immediate family. They also asked these people how much they thought of their family as an important part of who they are. The amount of contact with family was only weakly related to whether people evinced symptoms of depression, but identifying with their family was highly protective. The same result held for a different type of “family.” Among 150 members of an army unit from an Eastern European country, feeling closely associated with their unit seemed to stave off depression far better than simply spending time with other soldiers.

A number of other researchers have replicated this result. Along with University of Queensland psychologists Catherine Haslam and Jolanda Jetten, the three of us analyzed 16 studies, including more than 2,600 participants, to determine whether depression is related to how much a person identifies with a group. The groups ranged from support groups for patients recovering from heart surgery in Norway to students in secondary schools in Australia. As we reported earlier this year, the common finding across all studies was that the more someone identified with a group, the less severe his or her depression symptoms were. Thus, a sense of connection to a group, rather than just contact with individuals, is what protects mental health.

Groups also can serve as effective treatment for depression. We collaborated with Jetten, Catherine Haslam and psychologist Thomas Morton of the University of Exeter in England in a 2013 study that examined data from more than 4,000 English adults older than 50 that related to their current group memberships and depression symptoms. The surveys were completed several times over eight years. We found that group membership not only enabled nondepressed people to avoid the disorder but also powerfully aided recovery over time for people who had been depressed. Depressed respondents with no group memberships who joined a single group reduced their risk of relapse from 41 to 31 percent; among those who joined three groups, the risk of relapse dropped to 15 percent.

To be effective as therapy, however, the group you join must be important to you. In a study published this year we, along with Jetten and other colleagues, tested a group-based intervention in individuals at risk for depression as well as those diagnosed with it. We measured depression symptoms in 52 socioeconomically disadvantaged people at high risk for mental illness immediately after they joined a recreational group and three months later. We also asked individuals how much they identified with their group. Though just attending group meetings—to play soccer, make art, sew or do yoga—did not significantly lower depression scores, identifying with the group was associated with a marked decline in symptoms. Similarly, when we studied 92 people diagnosed with depression or anxiety who joined a therapy group in a psychiatric hospital clinic, we found that those who strongly identified with the therapy group were more than twice as likely to recover as those who felt only weakly connected to it.

Equal-Opportunity Remedy

Groups exert these powerful psychological effects because humans are social beings. We have evolved to act as part of a team. Indeed, researchers have found that just thinking about your social groups can make you less likely to get sick after being exposed to a virus, less apt to lash out at those who have wronged you and more tolerant of physical pain. Groups provide a sense of belonging. They also can give life meaning—something that is lost in depression—in part because we are better able to achieve goals when we work with others. Rates of depression and suicide drop markedly in wartime, for example, because people find meaning in working together to defeat an enemy. And of course, other members of your in-group can supply both emotional support and practical assistance in times of need.

Not all groups influence their members in positive ways, though. For instance, studies show that teenagers are much more likely to harm themselves if they hang out with others who self-harm. Two of us (Cruwys and Dingle) have found that breaking away from substance-using social groups is associated with a reduced risk of relapse among those in treatment for drug or alcohol abuse. In a 2010 study of First Nations adults in Canada, psychologist Amy Bombay, then at Carleton University, and her colleagues concluded that adopting a social identity associated with perceived discrimination might make a person more vulnerable to depression.

In general, however, social groups are antidotes to unhappiness, and joining them is a cost-effective adjunct to other depression treatments. Engagement with groups might also serve as a stand-alone strategy for those who cannot afford standard therapies or where there is a shortage of mental health professionals. Inexpensive treatments are critical given that the illness disproportionately affects those who are already socially and economically disadvantaged. Receiving therapy in a group can also help people unite to challenge prejudices against mental illness and to work out ways of moving forward together. Groups, then, are not only an effective shield against depression but also a sword that can puncture the stigma that accompanies it.