Dr. Lester Grinspoon (born June 24, 1928) is Associate Professor Emeritus of Psychiatry at Harvard Medical School. Grinspoon was senior psychiatrist at the Massachusetts Mental Health Center in Boston for 40 years. Dr. Grinspoon is a fellow of the American Association for the Advancement of Science and the American Psychiatric Association. He was founding editor of The American Psychiatric Association Annual Review and Harvard Mental Health Letter. Grinspoon was editor of Harvard Mental Health Letter for fifteen years.
Grinspoon was born June 24, 1928 in Newton, Massachusetts. He graduated from Tufts University and Harvard Medical School. He is married and the father of four children, including astrobiologist David Grinspoon and physician and author Peter Grinspoon. His oldest son died of cancer when he was 13. In 2011 he revealed that he had cancer during the documentary "Clearing the Smoke: The Science of Cannabis" 
Grinspoon became interested in marijuana in the 1960s when its use in the United States increased dramatically. He "had no doubt that it was a very harmful drug that was unfortunately being used by more and more foolish young people who would not listen to or could not believe or understand the warnings about its dangers." When Grinspoon began studying marijuana in 1967, his intention was to "define scientifically the nature and degree of those dangers" but as he reviewed the existing literature on the subject Grinspoon reached the conclusion he and the general public had been misinformed and misled. "There was little empirical evidence to support my beliefs about the dangers of marijuana," and he was convinced cannabis was much less harmful than he had believed. The title of Marihuana Reconsidered "reflected that change in view." He has testified before Congress, and as an expert witness in various legal proceedings, including the deportation hearings of John Lennon.
In 1990 Grinspoon won the Alfred R. Lindesmith Award for Achievement in the Field of Scholarship from the Drug Policy Foundation. The award is now given by the Drug Policy Alliance, which was formed in the year 2000 by a merger of the Drug Policy Foundation and The Lindesmith Center. Grinspoon endorsed Washington Initiative 1068 (2010) in May 2010.
Grinspoon is the author or co-author of several cannabis/psychedelic-related books, including Marihuana Reconsidered (publication dates 1971, 1977 and 1994), Psychedelic Drugs Reconsidered, Marijuana: The Forbidden Medicine and Psychedelic Reflections. The first two were published during the 1970s, when it appeared cannabis was well on its way to nationwide decriminalization in the United States. Marijuana: The Forbidden Medicine was published in 1993. It describes a variety of ailments for which cannabis ingestion may be indicated. Grinspoon contributed a chapter to Jefferson Fish's book How to Legalize Drugs.
Grinspoon runs two websites: Marijuana: The Forbidden Medicine that includes thousands of individual anecdotes concerning the medical uses of marijuana as well as Q&A; and Uses of Marijuana, which allows for people to submit essays relating to the 'enhancing' effects that marijuana can have on the user. The focus is on effects which are meaningful for the individual: not merely 'increased appetite', but rather effects such as increased creativity, rushes of insight/new ideas, or increased appreciation for music, art and nature.
Grinspoon appeared in an episode of the Showtime series Penn & Teller: Bullshit!. The episode, which addressed America's War on Drugs, aired in the show's second season. Grinspoon discussed the way marijuana helped his young son while he was dying from leukemia in the 1970s, completely eliminating the horrible nausea and vomiting he experienced after each of his chemotherapy treatments and, thereby, making the final year and a half of the boy's life far more comfortable, for his son, and for Grinspoon and his wife by not having to endure the pain of witnessing their son suffer. Grinspoon also appeared in the Canadian documentary The Union: The Business Behind Getting High and discussed the pharmaceutical characteristics of marinol, as well as his writing experiences with Carl Sagan. He appeared in the 2011 Montana PBS documentary Clearing the Smoke: The Science of Cannabis. Australian rock band Grinspoon are named after him.
- Lester Grinspoon. "Erowid Lester Grinspoon Vault". Erowid.org. Retrieved 2010-09-06.
- "Lester Grinspoon, M.D. - Harvard Health Publications". Health.harvard.edu. Archived from the original on 2010-07-03. Retrieved 2010-09-06.
- Lost in the Weeds: Legalizing Medical Marijuana in Massachusetts | Boston Magazine
- Clearing the Smoke: The Science of Cannabis. Montana PBS.
- Grinspoon & Bakalar. "Introduction to 1994 reprint of Marihuana Reconsidered". Rxmarijuana.com. Retrieved 2010-09-06.
- "John Lennon - Spring 1998 Cardozo Life". Cardozo.yu.edu. 1972-03-16. Retrieved 2010-09-06.
- "Achievement Awards". Reformconference.org. Retrieved 2010-09-06.
- "Drug Policy Alliance 10 Year Review" (PDF). Retrieved 2010-09-06.
-  Archived April 29, 2010, at the Wayback Machine.
- "Sensible Washington 2010 campaign endorsements for Initiative 1068". Retrieved 2010-09-06.
- Lester Grinspoon. "Erowid Library/Bookstore : 'Marihuana Reconsidered'". Erowid.org. Retrieved 2010-09-06.
- "Books | Psychedelic Drugs Reconsidered, Lester Grinspoon, James B. Bakalar". Lycaeum. Retrieved 2010-09-06.
- Grinspoon, L. (1998). Marihuana: An old medicine for a new millennium. In J. M. Fish (Ed.), How to legalize drugs (pp. 421-429). Northvale, NJ: Jason Aronson.
- Lester Grinspoon on IMDb
- "Clearing the Smoke: The Science of Cannabis". MontanaPBS. 2011-02-28. Retrieved 2015-10-22.