 Some American settlers claimed that smallpox could be prevented through the ingestion of lettuce , and an Iranian belief suggested consumption of the seeds when afflicted with typhoid . Folk medicine has also claimed it as a treatment for pain , rheumatism , tension and nervousness , coughs and insanity ; scientific evidence of these benefits in humans has not been found . The religious ties of lettuce continue into the present day among the Yazidi people of northern Iraq , who have a religious prohibition against eating the plant . 
