In 1967, Hanington hypothesized that oral tyramine caused headache in susceptible individuals. Since then, the studies on tyramine and headache have yielded conflicting results. All the studies use either a 24 or 48 hour period following tyramine ingestion to note whether headache developed. However, there is a considerable body of literature on "delayed reaction" type food sensitivities which notes a gap of as much as 72 hours between ingestion of offending foods and development of headache. When subjects receive tyramine capsules and placebo capsules 24 or 48 hours apart, it is conceivable that contamination of results could occur due to delayed reaction headaches. A headache following placebo ingestion could be a result of the delayed reaction to the tyramine. Numerous studies did not attempt to control for the ingestion of tyramine-rich foods in their subjects, and the failure to do so threatens the validity of their findings. Future studies need to consider a 72 hour time frame between tyramine and placebo trials, and any headaches developing for 72 hours after capsule ingestion should be recorded.