He believed that the cannabis plant should be decriminalized because it has been shown to be a renewable source of fuel, food, and medicine that can be grown in virtually any part of the world. He further asserts that the U.S. government deliberately hides the proof of this.
Herer ran for United States President twice, in 1988 (1,949 votes) and 1992 (3,875 votes) as the Grassroots Party candidate.
In July 2000, Herer suffered a minor heart attack and a major stroke, resulting in difficulties speaking and moving the right side of his body. Herer mostly recovered, and claimed in May 2004 that treatment with the Amanita muscaria, a psychoactive mushroom, was the "secret".
On September 12, 2009 Herer suffered another heart attack while backstage at the Hempstalk Festival in Portland, Oregon. He spent nearly a month in critical condition in a Portland hospital, including several days in a medically induced coma. He was discharged to another facility on October 13, 2009. Paul Stanford of The Hemp and Cannabis Foundation said "He is waking up and gazing appropriately when someone is talking... but he is not really communicating in any way." He died aged 70 on April 15, 2010 in Eugene, Oregon, from complications related to the September 2009 heart attack. Herer was buried at the Eden Memorial Park Cemetery in Mission Hills, California.
On August 12, 2012 a video was uploaded to YouTube of a man named Rick Simpson claiming that Jack Herer passed the torch of legalisation to him.
European experts on hemp, like Dr. Hayo M.G. van der Werf author of the doctoral thesis Crop physiology of fibre hemp (1994) and Dr. Ivan Bûcsa, criticized Herer' for making unrealistic claims regarding the potential of hemp, for example:
Herer claimed that hemp produces higher yields than other crops. Van der Werf argued that is simply wrong. Under most favorable growing conditions, other crops such as maize, sugar beet or potato produced similar dry matter yields. Fiber hemp is in no way exceptional. See also Hemp#Yield in modern agriculture
Herer claimed that hemp hurds, which make up 60 to 80% of the stem dry weight, contain 77% cellulose. Van der Werf argued that is wrong. Cellulose content of hemp hurds has been found to vary between 32 and 38% (Bedetti and Ciaralli 1976, van der Werf 1994). Possibly, Herer confused the hurds, which form the woody core of the hemp stem, with the bark, which forms the outer layer of the hemp stem. The bark contains the long bast fibers which are used in textile manufacturing.
Herer claimed that hemp could be grown on 6 million hectares in the European Union, something that should have produced millions of tons of hemp fiber. The present production of hemp fiber in EU is only around 0.023 million ton/year. Dr. Ivan Bûcsa argues that it was a great exaggeration to expect millions of tons since it is not worth transporting unprocessed hemp more than 40–50 km even in bales.
The Emperor Wears No Clothes (1985, 1990) [and online edition, text only]
G.R.A.S.S.: Great Revolutionary American Standard System [with Al Emmanuel] (1973)