Tryptophan is most commonly associated with sleeping through arguments on Thanksgiving, but its stereoisomer l-tryptophan (same molecular makeup, different physical shape) is used to treat mood disorders like bipolar disorder and depression in addition to insomnia. Back on the market since 2008, L-tryptophan was banned for 19 years after being linked to a previously unrecognized disease, dubbed eosinophilia-myalgia syndrome (EMS). The FDA recalled products containing the compound after finding that contaminants were causing EMS, the symptoms of which range from discolored rashes and hair loss to neurological impairment and tumors. The disease has killed at least 37 people, according to the National Eosinophilia-Myalgia Syndrome Network. To be clear, you can't get EMS from eating too much turkey, which doesn't actually have high levels of tryptophan.