Errors in Administration of the Dexamethasone Suppression Test

To the Editor.—  Greden et al¹ reported that some of their patients with suppressive responses to the dexamethasone suppression test (DST) became nonsuppressors after withdrawal from antidepressants, and they hypothesized a causal effect. We have recently reported² the case of a non-depressed patient with a suppressive DST response in whom withdrawal from antipsychotics led to nonsuppression in response to the DST (a positive DST) on two separate occasions. The antipsychotic used was piperacetazine, which has marked anticholinergic properties.Both reports have suggested that anticholinergic withdrawal with subsequent cholinergic overdrive induces nonsuppression in response to the DST, as happens with the administration of physostigmine to normal subjects.³ Taken together, these data provide strong support for this being the mechanism of action. Carroll et al⁴ reported that neuroleptic treatment has no effect on the DST, but it is possible that withdrawal of neuroleptics with strong anticholinergic properties may give