Excessive 5-HTP stimulation may cause "serotonin syndrome", which is an excess accumulation of serotonin in the synapses. This syndrome is characterized by altered mental states, problems performing independently, and muscle control problems.

The Food and Drug Administration released an alarming report in 1998. The report stated that a chemical compound known as "peak X" was detected in some 5-HTP products. Peak X may cause a disabling and sometimes fatal blood disorder. This chemical was the reason that tryptophan was taken off the market. Since the body turns tryptophan into 5-HTP, the latter has been considered a safe replacement for the banned tryptophan. It was assumed that 5-HTP could not possibly present the same risks because it was manufactured completely differently. However, a recent discovery of the same substance in batches of 5-HTP has many wondering about its safety. At this time of this report, there is no other information from the FDA on using 5-HTP, but you should keep informed on any reports that may follow up this finding. There is a likelihood that this is an instance of contamination and is isolated to this one report.