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To the Editor.—
The article by Pickar et al (Archives 35:1378-1383, 1978) on the relationship of changes in excretion of 3-methoxy-4-hydroxyphenethylene glycol (MHPG) and remission of depressive symptoms at the time of follow-up requires a cautionary note. The most important finding was that the ratio of follow-up-baseline levels of MHPG was higher in the six patients whose conditions were in remission than in the four whose conditions were not.The difficulty in interpreting this is that a variable known to affect outcome was not controlled: treatment with drugs. Three of the six patients whose conditions were improved had been receiving drugs before the 21day drug-free period prior to evaluation. Only one of the four whose conditions did not improve had received drugs. In the absence of a prospective study, holding known relevant variables constant, we cannot conclude that the finding by these authors is unambiguous. It may very well be true
Rifkin A, Quitkin F. MHPG Excretion. Arch Gen Psychiatry. 1979;36(9):1030. doi:10.1001/archpsyc.1979.01780090116013