As an affiliate of the US Public Health Service, he served in outpatient clinics in California and Oregon and was chief pharmacist of the outpatient clinic in Washington, D.C. When the National Clearinghouse for Poison Control Centers came into being in 1957, he was named assistant director. He has co-authored numerous articles which have appeared in many publications on the subject of poison control.

In 1960 he was named director of the clearinghouse, a position he held for eleven years. In 1972 he was reassigned to the Hazardous Substance Department of the Federal Drug Administration. In 1965 he was awarded the Public Health Service Meritorious Medal for his work in the Poison Control Center development. In 1975 he received the Distinguished Alumnus Award from the U. of W. School of Pharmacy for work done in poison control activities.

In 1960 Surgeon General Leroy Burney, M.D., wrote “We established in 1957 a National Clearing House for Poison Control Center within the Public Health Service. This clearinghouse has functioned as a coordinating and research service to hundreds of local centers throughout the nation.” Thanks to the work of Henry Verhulst and other pioneers in the field, Americans currently have a national toll-free hot line for poison emergencies 24 hours a day, seven days a week.