Lena H. Sun / The Washington Post

For ADHD, the definition is being broadened, meaning the disorder could be diagnosed in more children. In the case of autism, the opposite is true.

The new criteria are among the changes that will be released with the publication this weekend of the long-awaited guidebook that psychiatrists and other mental health clinicians use to diagnose mental disorders. It’s the first major update in nearly 20 years. The 947-page tome by the American Psychiatric Association adds some new disorders, broadens criteria for existing ones and tightens them for other illnesses.

The highly controversial decisions involved in producing the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders, or DSM-5, have a potentially broad impact: They can affect which services children receive in schools, what treatments patients receive from doctors and even how people are viewed by society.

Experts involved in the guidebook say the changes will give clinicians greater precision in diagnoses and treatments. Critics counter that the new language will make it too easy to turn the stresses of ordinary life into mental illnesses.

For the first time, for example, someone who experiences severe grief after the death of a loved one could receive a diagnosis of major depressive disorder.

A patient whose mental decline is mild, but seems more serious than normal, could receive a diagnosis of mild neurocognitive disorder, which is new to the DSM-5.

Also new: Someone who repeatedly overeats could get a diagnosis of binge-eating disorder. A person who allows possessions to fill up their home could have hoarding disorder. The manual also spotlights conditions, such as Internet gaming disorder, that merit further research before being included as official diagnoses.

The handbook plays a big role in American society. It determines which diagnostic codes medical professionals use for specific patients and can affect whether health insurance pays for treatment. The DSM’s wording also can dictate which social services people are entitled to.

Long before the DSM-5’s official release, scheduled today at the psychiatric association’s annual meeting in San Francisco, the publication drew intense fire.

Thomas Insel, director of the National Institute of Mental Health, the largest mental health research organization in the world, set off a furor when he said the manual lacked validity. He said the NIMH would shift its research away from the DSM categories — and their symptom-based criteria. Instead, new research would focus more on areas such as the biology of brain circuits and the behavior they produce, as well as emerging clinical data.

“While DSM has been described as a ‘Bible’ for the field, it is, at best, a dictionary, creating a set of labels and defining each,’” he wrote in a blog post.

For example, in major depression, one symptom is anhedonia, the loss of pleasure in things someone used to enjoy. But that loss also can refer to someone’s “willingness to go get things you like,” and those are two different brain circuits, said Bruce Cuthbert, coordinator of the NIMH’s new research project.

So even if people have the same symptom of depression and receive the same diagnosis, what they really suffer from may be different. Treatment doesn’t work for everybody, he said.

David Kupfer, the chairman of the task force that oversaw the development of the revised guidebook, rejected criticism that the changes would increase the number of people who receive diagnoses of mental disorders, saying the number of disorders is essentially the same. Some new ones were added because research and public health data indicate they are “ready for prime time,” he said in an interview.

“When all is said and done, we’re not concerned that we’ve created many new disorders ... or that we’re going to add to the number of people who will be diagnosed with mental illness,” Kupfer said.