Andrew Thomas Weil was born in Philadelphia on June 8, 1942, the only child of parents who operated a millinery store, in a family that was Reform Jewish. He graduated from high school in 1959 and was awarded a scholarship from the American Association for the United Nations, giving him the opportunity go abroad for a year, living with families in India, Thailand, and Greece. From this experience he became convinced that in many ways American culture and science was insular and unaware of non-American practices. He began hearing that mescaline enhanced creativity and produced visionary experiences, and finding little information on the subject, he read The Doors of Perception by Aldous Huxley.

Weil entered Harvard University in 1960, majoring in biology with a concentration in ethnobotany. He had an early curiosity regarding psychoactive drugs, and in that period, met Harvard psychologists Timothy Leary and Richard Alpert, and separately engaged in organized experimentation with mescaline (along with fellow undergraduate Ronnie Winston). Weil would write for and eventually serve as an editor of the Harvard Crimson. One published account of the period describes a falling out of Weil from the group that included the faculty—among whom the experimentation with drugs was contentious, and with regard to undergraduates, proscribed; the falling out involved an exposé on drug-use and supply that Weil wrote for the Crimson. Weil wrote of faculty experimentation with drugs in a series of Crimson pieces:

Weil’s undergraduate thesis was titled “The Use of Nutmeg as a Psychotropic Agent,” specifically, on the narcotic properties of nutmeg, inspired by a class with David McClelland, chair of the Department of Social Relations, and a former director of Harvard’s Center for Research in Personality. In 1964, he graduated cum laude with a B.A. in biology.

Weil entered Harvard Medical School, “not with the intention of becoming a physician but rather simply to obtain a medical education.” He received a medical degree in 1968, although “the Harvard faculty… threatened to withhold it because of a controversial marijuana study Weil had helped conduct” in his final year. Weil moved to San Francisco and completed a one-year medical internship at Mount Zion Hospital in 1968–69. While there, volunteered at the Haight-Ashbury Free Clinic. Weil went on to complete one year of a two-year program at NIH, resigning due to “official opposition to his work with marijuana.”

Weil’s 1983 Chocolate to Morphine roused the ire of Florida senator Paula Hawkins, “who demanded that the book, a veritable encyclopaedia of various drugs and their effects on humans, be removed from schools and libraries.”

In 1994, Weil founded the Arizona Center for Integrative Medicine at the University of Arizona College of Medicine in Tucson, Arizona, where he serves as its director.

Weil appeared on the cover of Time magazine in 1997 and again in 2005, and Time named him one of the 25 most influential Americans in 1997 and one of the 100 most influential people in the world in 2005. He was inducted into the Academy of Achievement in 1998. His “Ask Dr. Weil” website was chosen by Forbes’ Best of the Web Directory in 2009 for having offered “straightforward tips and advice on achieving wellness through natural means and educating the public on alternative therapies.”

Medical professionals in particular have criticized Weil for promoting treatment claims and alternative medicine practices described as unverified or inefficacious, or for otherwise rejecting aspects of evidence-based medicine. Weil’s rejection of some aspects of evidence-based medicine and his promotion of alternative medicine practices that are not verifiably efficacious were criticized in a 1998 New Republic piece by Arnold S. Relman, emeritus editor-in-chief of The New England Journal of Medicine and emeritus professor of medicine at Harvard Medical School. The late Barry Beyerstein of Simon Fraser University, writing in the journal Academic Medicine in 2001, criticized Weil and various aspects of complementary and alternative medicine, asserting that it held a “magical world-view”; he continued, saying,

In 2003, Steven Knope, author of The Body/Mind Connection (2000), a physician trained at Weill Cornell Medical College, and former Chair of the Department of Medicine in the Tucson, Arizona, Carondelet system, criticized Weil in a televised discussion for what he considered irresponsible advocacy of untested treatments. Simon Singh, a recognized British science writer, and Edzard Ernst, a former Professor of Complementary Medicine at the University of Exeter, echoed Beyerstein’s criticism in their 2008 book Trick or Treatment, saying that while Weil correctly promotes exercise and smoke-free lifestyles, “much of his advice is nonsense.”

Hans Baer of the Department of Sociology and Anthropology at the University of Arkansas, writing in 2003, has argued that Weil’s approach represents a general limitation of the holistic health/New Age movement, in its “tendenc[y] to downplay the role of social, structural, and environmental factors in the etiology of disease” in the United States, and in doing so, represents a failure to “suggest substantive remedies for improving access to health care,” generally, for the “millions of people who lack any type go health insurance…”; at the same time, Baer notes (with negative connotations) that Weil instead contributes “to a long tradition of entrepreneurialism in the U.S. medical system.”

The Forbes article noted, in particular, drugstore.com’s 2005 lawsuit against DrWeil.com for Weil’s having “failed to perform any of his marketing obligations,” noting that in a 2004 Larry King Live interview, Weil failed to promote this business partner, despite the program offering “reasonable opportunity for Weil to use efforts to promote drugstore.com.” Moreover, the CSPI’s newsletter noted that their investigations into the vitamin and supplement recommendation service led them to conclude that the algorithms behind the recommendations were, by default, set to recommend purchases: regardless of how the online inquiries of the personalized service were answered, “we couldn’t get the Advisor to stop recommending that we buy supplements.” The CSPI article concludes, “Beware of doctors who sell what they recommend.”

Beginning in 2006, as the result of his commercial ventures, Weil—as David Gumpert has described—has placed himself in the “awkward position of… having to defend himself against charges of inappropriately exploiting his medical-celebrity status.” Commenting on a cover article in a recent 2006 edition of the Center for Science in the Public Interest’s “highly respected” Nutrition Action Healthletter, Gumpert called attention to:

In 2006, the Center for Science in the Public Interest also commented on a Time magazine piece by Weil rebutting a recent JAMA report on the failure of fish oil supplements to significantly reduce risk of serious heart arrhythmias, where he emphasized the benefits of fish oil supplements without a disclaimer that he had a direct commercial interest in the sale of these supplements.

In 2009, the US Food and Drug Administration sent a warning letter to Weil’s Weil Lifestyle LLC, regarding “Unapproved / Uncleared / Unauthorized Products Related to the H1N1 Flu Virus” in particular, a “Notice of Potential Illegal Marketing of Products to Prevent, Treat or Cure the H1N1 Virus H1N1 [influenza] Virus.” The FDA was primarily concerned with several implicit claims in Weil Lifestyle LLC’s marketing literature, that certain products could help ward off such viruses.

Weil blogs for the Huffington Post and has been a frequent guest on “Larry King Live” on CNN, Oprah, and the “Today” Show. Weil appeared in the 2012 documentary on the need for a “rescue” of American healthcare, Escape Fire. He also appeared in the 2019 documentary Fantastic Fungi.

As of 2015, Weil was serving as series editor of an academic imprint from Oxford University Press called the Weil Integrative Medicine Library, volumes for clinicians in more than 10 medical specialties, including oncology, cardiology, rheumatology, pediatrics, and psychology. Weil co-edited the first volume, Integrative Oncology, with Donald Abrams, which appeared in 2009. Academic and scholarly reviews of the series and individual volumes were lacking as of 2015—in almost all cases, the publisher’s “Reviews and Awards” tabs lack society or other published reviews (apart from Doody’s). A cancer society review of the second edition of the series’ Integrative Oncology volume, the first volume to have been published, describes the field as “an exciting new discipline” and the book as offering “best-practice methods to prevent cancer and support those affected by it on all levels: body, mind, and spirit” and as being comprehensive, and offering “meticulous, well-written chapters on proven and yet-to-be-proven methods for enhancing cancer care with integrative oncology.”