Riddelliine is a chemical compound classified as a pyrrolizidine alkaloid. It was first isolated from and is also found in a variety of plants including Jacobaea vulgaris, Senecio vulgaris, and others plants in the genus Senecio. Riddelliine can be found as a contaminant in foods such as meat, grains, seeds, milk, herbal tea, and honey. Riddelliine is suspected to be a carcinogen. It is listed as an IARC Group 2B carcinogen and listed by the National Toxicology Program in its Report on Carcinogens which lists chemicals "known or reasonably anticipated to cause cancer in humans".