SAN FRANCISCO — Ann Shulgin, who together with her late husband Alexander Shulgin pioneered the use of psychedelic drugs in psychotherapy and co-wrote two seminal books on the subject, has died at the age of 91.

Shulgin had been in ill health because of chronic obstructive pulmonary disease, her daughter, Wendy Tucker, said. She died Saturday at “the farm,” a sprawling San Francisco Bay Area residence she shared with her chemist husband until his death in 2014, surrounded by loved ones, Tucker said.

Shulgin had a deep understanding of Jungian psychoanalysis and collaborated with her husband, who in the 1970s rediscovered the MDMA compound, better known as ecstasy, and introduced it as a possible mental health treatment. The couple tested the substances on themselves and a small group of friends.

“He was the scientist, and I was the psychologist,” Shulgin said of their partnership in a 2014 interview with The Associated Press. “He was a genius.”

Born in New Zealand to an American diplomat and New Zealand mother, Shulgin grew up in different parts of the world. The family settled in San Francisco after her father’s retirement. A professionally trained artist, Shulgin drew and painted all her life and worked as a medical transcriber.

In 1978, she met Alexander Shulgin, who created more than 200 chemical compounds for use in psychotherapy.

The couple’s home, where Alexander Shulgin also had his lab, in Lafayette, California, about 22 miles (35 kilometers) east of San Francisco, for decades was a gathering place for students, teachers and those working with psychedelics.

Though she was not a professionally trained psychotherapist, “she was always the one who people talk to and you always felt like you could open up to her. She called herself a lay therapist,” Tucker said.

The couple took copious notes of their experiences and of what they observed in others and co-wrote two books. PiHKAL: A Chemical Love Story, which was published in 1991, and TiHKAL: The Continuation, published in 1997.

In PiHKAL, Shulgin wrote about her first experience with psychedelics when she was in her 20s.

“I saw something forming in the air, slightly above the level of my head. I thought that it was perhaps a few feet from me, then I realized I couldn’t actually locate it in space at all. It was a moving spiral opening, up there in the cool air, and I knew it was a doorway to the other side of existence, that I could step through it if I wished to be finished with this particular life I was living, and that there was nothing threatening or menacing about it; in fact, it was completely friendly. I also knew that I had no intention of stepping through it because there was still a great deal I wanted to do in my life, and I intended to live long enough to get it all done. The lovely spiral door didn’t beckon; it was just matter-of-factly there,” she wrote.

Publishers were afraid to print their first book about MDMA so the couple, who were against ecstasy being used outside of therapy, self-published it because they wanted to share their experiences and knowledge with the world, Tucker said.

“They were the ones pushing to do all the PTSD work with veterans with MDMA because they saw people who had severe trauma could really break through. They were so brave to publish their work because that really opened the door and paved the way to all that is happening now,” Tucker said.

In the U.S., several states have approved studying the potential medical use of psychedelics, which are still illegal under federal law. A string of cities have also decriminalized so-called magic mushrooms, and an explosion of investment money is flowing into the arena.

Experts say the research is promising for treating conditions ranging from PTSD to smoking addiction, but caution that some serious risks remain, especially for those with certain mental health conditions.

“We lost years and years of research ability because of the attitude and fears around psychedelics. But we wouldn’t be where we are if it wasn’t for Ann and Sasha,” she added.

Shulgin is survived by four children, eight grandchildren and five great-grandchildren. A memorial is being planned for later in the year.