Dr. Humphreys has been extensively involved in the formation of public policy, having testified to U.S. House and Senate Committees and in many state legislatures, and having served on the White House Commission on Drug-Free Communities during the Bush Administration and as Senior Policy Advisor in the White House Office of National Drug Control Policy under President Obama. He created and co-directs the Stanford Network on Addiction Policy, which brings scientists and policy makers together to improve public policies regarding addictive substances. He also leads the Stanford-Lancet Commission on the North American Opioid Crisis.

Dr. Humphreys has also testified on numerous occasions in the U.K. Parliament and advises multiple U.K. government agencies. He and the authors of "Drug Policy and the Public Good" won the 2010 British Medical Association's Award for Public Health Book of the Year. To recognize his service to addiction-related services and scholarship in Britain Queen Elizabeth made him an Honorary Officer in the Order of the British Empire in 2022.