Assertion: tryptophan | /r/HasProperty | sole precursor
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text: To get their share of the profitable marketing of serotonin as the vehicle to "emotional bliss", and to distinguish themselves from the drug companies, many supplement promoters have been claiming that tryptophan, the sole precursor for serotonin, is an effective, cheaper alternative to the serotonin-enhancing medications, and that this alternative is allegedly devoid of tryptophan side effects because it is a "natural" substance (some people have called it “