Paula J. Caplan, a psychologist who challenged the sexist assumptions that she identified in her profession — among them, a tendency to blame mothers for their children’s problems — in a decades-long campaign to improve mental health care for women, died July 21 at her home in Rockville, Md. She was 74.

The cause was metastatic melanoma, said her daughter, Emily J. Caplan Stephenson.

Dr. Caplan, a clinical psychologist and longtime professor at the University of Toronto, embarked on her career in the early 1970s. Only a decade earlier, feminist writer Betty Friedan had identified in her book “The Feminine Mystique” a pervasive malaise among unfulfilled housewives that she labeled “the problem that has no name.”

Dr. Caplan, one of several prominent psychologists who sought to bring a feminist worldview to their field, argued that for generations, male psychologists had labeled women’s problems with the wrong name — a systemic failing that, she argued, resulted in untold numbers of women receiving one diagnosis when they should have received another, or even none at all.

She assailed the concept of female masochism, an idea rooted in Freudian psychoanalysis according to which women take pleasure in dissatisfaction and suffering. In her 1985 book, “The Myth of Women’s Masochism,” Dr. Caplan sought to demonstrate the concept’s pernicious effects as it became ingrained in psychology and the popular imagination.

Battered women, she noted, were labeled masochists when in fact they remained in abusive relationships to avoid the greater suffering that they feared might come from leaving — a potential reprisal from the abusive partner, loneliness or indigence.

Countering another belief among some psychologists, she argued that women who sacrifice their needs or desires to give more fully of themselves to their children are not bearing out Freudian ideas of female masochism, but rather are fulfilling the nurturing maternal role that society expected them to play.

“The same behaviors that are defined as masochistic in women,” Dr. Caplan told the New York Times in 1985, “would be defined quite healthily as sacrificial, or courageous, or facing realities, or hard work, in men.’’

Psychology’s mistreatment of women, according to Dr. Caplan, extended to pinning blame on them for the mental disturbances of their children. Among her clinical colleagues, she noted what she regarded as a disturbing tendency to use mothers as psychiatric scapegoats, a trend she addressed in her book “Don’t Blame Mother: Mending the Mother-Daughter Relationship” (1989).

Reviewing a series of studies published in the 1970s and 1980s, she observed that “mothers were blamed for 72 different kinds of problems in their offspring, ranging from bed-wetting to schizophrenia, from inability to deal with color blindness to aggressive behavior, from learning problems to ‘homicidal transsexualism.’ ”

Dr. Caplan attracted particular attention for her opposition to the official classification of premenstrual dysphoric disorder, a severe form of premenstrual syndrome, in the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders, a widely used guide known as the DSM. In the first place, she argued, PMS symptoms were the result of natural fluctuations in a woman’s hormone levels.

“If they had made a decision suddenly pathologizing a half million men, there would be a public outcry,” Dr. Caplan told the Times in 1994, expressing her disagreement with colleagues who supported labeling severe PMS a mental illness.

The argument in favor of classifying the condition as a mental disorder, Dr. Caplan’s detractors said, was that it might encourage research on the subject and help affected women feel justified in seeking help. But in a broader assessment of psychology, Dr. Caplan maintained that a diagnosis of mental disorder could, in some scenarios, bring about real consequences.

“Since the 1980s, when I first made public my concerns about psychiatric diagnosis, I have heard from hundreds of people who have been arbitrarily slapped with a psychiatric label and are struggling because of it,” she wrote in The Washington Post in 2012.

“About half of all Americans get a psychiatric diagnosis in their lifetimes,” she continued, which “can cost anyone their health insurance, job, custody of their children, or right to make their own medical and legal decisions. . . . In light of the subjectivity of these diagnoses and the harm they can cause, we should be extremely skeptical of them.

Dr. Caplan ultimately concluded that the DSM should be “thrown out.”

“In our increasingly psychiatrized world, the first course is often to classify anything but routine happiness as a mental disorder, assume it is based on a broken brain or a chemical imbalance, and prescribe drugs or hospitalization,” she wrote her Post commentary.

Earlier, she had gone so far as to declare psychology an “overrated” field.

“Psychologists and psychiatrists can do wonderful things. But these days you would think that there is no such thing as normal,” she wrote in the Times in 2003. “If you are still grieving a loved one’s death two months later, you fit the category of ‘major depressive disorder.’ Insurance companies want you quickly fixed, drug companies have a pill for every occasion, and friends and family are too overworked to provide the irreplaceable support for grief that is present in other countries. We are damaging the nature of friendship, teaching people that they need experts to treat them for everything.”

Paula Joan Caplan was born in Springfield, Mo., on July 7, 1947. Her father, who worked in real estate, had served in the military during World War II and inspired Dr. Caplan’s later work on behalf of traumatized veterans who, in her opinion, society shuttled into mental health treatment without deeper interest in their needs.

“Simply sending frightened, angry soldiers off to therapists conveys disturbing messages: that we don’t want to listen, that we’re afraid we’re not qualified to listen, and that they should talk to someone who gets paid to listen,” she wrote in The Post in 2004. “The implication is that their devastation is abnormal, that it is a mental illness, and this only adds to their burdens.”

After receiving a bachelor’s degree in English from Radcliffe College in 1969, Dr. Caplan enrolled at Duke University, where she received a master’s degree in 1971 and a PhD in 1973, both in psychology. Dr. Caplan’s mother, who died in February at 97, pursued graduate studies in counseling just as her daughter began hers.

Dr. Caplan was on the faculty of the University of Toronto from 1979 to 1995. She later taught at institutions including Brown University, American University and Harvard University, where she was director of the Voices of Diversity Project at the Hutchins Center for African and African American Research.

Dr. Caplan's books included "Lifting a Ton of Feathers: A Woman's Guide to Surviving in the Academic World" (1993), "Thinking Critically About Research on Sex and Gender" (1994, co-authored with her son, Jeremy B. Caplan) and "They Say You're Crazy: How the World's Most Powerful Psychiatrists Decide Who's Normal" (1995).

In addition to her academic work, she wrote plays and produced documentary films including "Isaac Pope: The Spirit of an American Century" (2019), about a 100-year-old African American veteran of World War II and his experience of racism through the 20th century.

Dr. Caplan's marriages to Paul Mohl and Marcel Kinsbourne ended in divorce.

Survivors include two children from her second marriage — her daughter, of Rockville, and her son, of Edmonton, Alberta; a brother; and five grandchildren.

"I love proving and stating that what men are saying about women is wrong," Dr. Caplan once told the Toronto Star, reflecting on her work. "There are a lot of myths that are used to oppress women that are based on sloppily gathered data, biased theories and outright misogynism. Mental health professionals must take the responsibility to undo the damage and show what is positive about women."