LSD and 5-HTP: tolerance and cross-tolerance relationships

Tolerance and cross-tolerance relationships between lysergic acid diethylamide (LSD) and 5-hydroxytryptophan (5-HTP) were studied in rats trained on an operant task. The results demonstrated that behavioral tolerance to both compounds occur in the rat and that asymmetrical cross-tolerance relationships exist; that is, animals tolerant to 5-HTP were cross-tolerant to LSD, but animals tolerant to LSD were not cross-tolerant to 5-HTP.