There were some deaths associated with L-Tryptophan years ago. They did take it off the market, although it was unclear if that was a fully thought out decision.
There was a problem that was attributed to the product over and above deaths, but I don’t remember exactly what it was, or if it was completely disassociated with the adulterated product.
I remember now that it had to do with blood disorders ... people were taking it for anti-depression and sleep problems. They were taking too much per day ... I think about ten people died ....
At the time there was a lot of speculation that the genetically engineered bacteria that the company used to create it caused the problems but I think that was eventually dismissed.
In any event while whatever the production problems was it was fixed but the FDA banned it as did a lot of countries. They removed the restriction in 2001 but I think they still have a warning that large doses might result in the inability to break histamines (which a lot of people think was the cause of the initial problems).