Melody Beattie, whose experiences as a drug addict, a chemical dependency counselor and the wife of an alcoholic informed a best-selling book about codependence that has guided countless people to shed toxic relationships, died on Feb. 27 in the Los Feliz neighborhood of Los Angeles. She was 76.

Her daughter, Nichole Beattie, said the cause was heart failure. She had been hospitalized from Nov. 30 to Dec. 12, then evacuated from her home in Malibu because of a wildfire and moved into her daughter’s home, where she died.

By popularizing the concept of codependence, Ms. Beattie (pronounced BEE-tee) became a literary star in the self-help world with “Codependent No More: How to Stop Controlling Others and Start Caring for Yourself” (1986), which has sold more than seven million copies worldwide.

“You could call her the mother of the self-help genre,” said Nicole Dewey, the publishing director of Spiegel & Grau, which has sold more than 400,000 copies of the book since taking over publication in 2022.

Trysh Travis, the author of “The Language of the Heart: A Cultural History of the Recovery Movement From Alcoholics Anonymous to Oprah Winfrey” (2009), said in an interview that “Codependent No More” has succeeded because of Ms. Beattie’s common-sense approach and “vernacular charm.”

She added: “There had been other books and pamphlets published in the recovery space in the early 1980s. Melody made the same arguments, but her voice came across very clearly. It wasn’t clinical — and she had a set of ideas that could be applied to many if not all the problems one was having — and it hit the market at the right time.”

In “Codependent No More,” Ms. Beattie cited various definitions of a codependent person. She also introduced one of her own.

“A codependent person,” she wrote, “is one who has let another person’s behavior affect them and who is obsessed with controlling that other person’s behavior.”

The other person, she wrote, might be a family member, a lover, a client or a best friend. But the focus of codependency “lies in ourselves, in the ways we let other people’s behaviors affect us and in the ways we try to affect them” — by actions that include controlling them, obsessively helping them and caretaking.

Recalling her difficult marriage to her second husband, David Beattie, who was also a substance abuse counselor, Ms. Beattie described an incident when he was in Las Vegas. She telephoned him in his hotel room, and he sounded as if he had been drinking. She implored him not to break his promise to her that he would not get drunk on this trip. He hung up on her.

In desperation, she called the hotel repeatedly into the night, even as she was preparing to host a party for 80 people at their house in Minneapolis the next day.

“I thought if I can just talk to him, I can make him stop drinking,” she told The Minneapolis Star Tribune in 1988. But at 11 p.m., she stopped calling.

“Something happened inside of me, and I let go of him,” she said. “I thought, ‘If you want to drink, drink. …’ I gave his life back to him, and I started taking my own back.”

She said that was the first step in detaching herself from their mutual codependence. They eventually divorced.

Detachment, she wrote, “is not a cold, hostile withdrawal” or a “Pollyannish, ignorant bliss”; rather, it is releasing “a person or problem in love.”

When should the release happen? she asked. Her list was long. It started: “When we can’t stop thinking, talking about, or worrying about someone or something; when our emotions are churning and boiling; when we feel like we have to do something about someone because we can’t stand it another minute. …”

Melody Lynn Vaillancourt was born on May 26, 1948, in Ramsey, Minn., and grew up mainly in St. Paul. Her father, Jean, a firefighter, was an alcoholic who left the family when Melody was 2. Her mother, Izetta (Lee) Vaillancourt, owned a nursing home after her divorce, but, Ms. Beattie said, beat her four siblings. (She escaped the punishment herself, she said, because she had a heart condition.)

Melody was sexually molested by a stranger when she was 5; began drinking whiskey at 12; and started using amphetamines, barbiturates, LSD and marijuana in high school. By 20, she was shooting heroin. She also robbed pharmacies with a partner and, after being arrested, spent eight months in drug treatment in a state hospital.

After being successfully treated, she held secretarial jobs before being hired as a chemical dependency counselor in Minneapolis, assigned to treat the wives of men in treatment. Her patients were uniformly angry and focused so much on their husbands’ feelings that she found it nearly impossible to get them to express their own.

“Eight years later, I understood those codependents, those crazy codependents — we didn’t call them that, we called them significant others — because I had become one” through her marriage to Mr. Beattie, she told The Star Tribune. “All I could think and talk about was the alcoholic, what he was or wasn’t doing.” She was, she said, “filled with anger and anger because he wouldn’t stop drinking.”

While treating the women, living on welfare and writing freelance articles for a local paper, The Stillwater Gazette, she interviewed experts on codependence, hoping to write a book on the subject.

She received a $500 advance from the publishing division of the Hazelden Foundation substance abuse recovery center, now called the Hazelden Betty Ford Foundation. The book was published in 1986 and spent 129 weeks on The New York Times’s advice and how-to best-seller list.

Ms. Beattie went on to write several other books, including “The Language of Letting Go: Daily Meditations on Codependency” (1990), which has sold more than three million copies.

Writing in Newsweek in 2009, Dr. Drew Pinsky, the addiction medicine specialist and media personality, named “Codependent No More” one of the four best self-help books of all time. Ms. Beattie heavily revised it for a new edition that was published in 2022.

In addition to her daughter, Ms. Beattie is survived by two grandsons; a sister, Michelle Vaillancourt; and a son, John Thurik, from her first marriage, to Steven Thurik, which ended in divorce. John was raised by his father and maternal grandmother.

Her marriages to Scott Mengshol and Dallas Taylor, who played drums with Crosby, Stills, Nash & Young, also ended in divorce.

Her son Shane Beattie died in a skiing accident in 1991 when he was 12, plunging her into grief. She wrote “The Lessons of Love: Rediscovering Our Passion for Life When It All Seems Too Hard to Take” (1995) — a personal book, not a self-help guide — to describe her journey from a broken spirit to recovery.

Her first step was to write two letters, one of which said:

“God, I’m still mad, not pleased at all. But with this letter, I commit unconditionally to life, to being here and being alive as long as I’m here, whether that’s another 10 days or another 30 years. Regardless of any other human being and their presence in my life, and regardless of events that may come to pass. This commitment is between me, life, and you.”