Dr. Gabriel Nahas, a controversial medical researcher who became a prominent crusader against marijuana after being shocked to hear, at a PTA meeting in 1969, about the drug’s widespread use, died June 28 in Manhattan. He was 92.

The cause was a respiratory infection, his family said.

Nahas did research to find the physiological effects of smoking marijuana, wrote 10 books on the drug and became a leader of anti-drug organizations. He was a visible ally of Nancy Reagan in her “just say no” to drugs campaign as the first lady in the 1980s.

Nahas saw his anti-drug campaign as nothing less than a continuation of the fight against totalitarianism, which for him began during World War II as a decorated leader of the French Resistance; like totalitarianism, he believed, drugs enslaved the mind. He was awarded the Legion of Honor by France, the Presidential Medal of Freedom by the U.S. and the Order of the British Empire for his wartime heroism.

His research, which he did as a professor at Columbia University and reported in more than 700 articles in scientific journals, suggested that marijuana contributed to cancers of the head and neck, leukemia, infertility, brain damage and a weakening of the immune system. He also wrote two books on cocaine, which he contended could cause irreversible brain damage.

Nahas became known as much for his advocacy as for his science. He was the chairman of the scientific advisory committee of the National Federation of Parents for Drug-Free Youth, now the National Family Partnership. He was a consultant to the U.N. Commission on Narcotics in the 1980s and ’90s. In 1985, he appeared at an anti-drug rally with Reagan and the actor William Shatner, who was in costume as his best-known character, Captain Kirk of “Star Trek.” Nahas testified frequently at government hearings.

His critics in the scientific community sometimes assailed his methodology, questioning the large judgments he made often based on small samples. Organizations promoting the decriminalization or legalization of marijuana painted him as a villain. The New England Journal of Medicine once described his work as “psychopharmacological McCarthyism that compels him to use half-truths, innuendo and unverifiable assertions.”

But Robert DuPont, drug czar in the Nixon and Ford administrations, called Nahas “the Paul Revere of drug abuse,” saying, “He alone lit the beacon warning of the threat of the modern drug abuse epidemic.”