MHPG Excretion

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