# 19 - Dexamethasone suppression test (DST)

# Dexamethasone suppression test (DST)

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neurons in the basolateral amygdala may occur, contributing to a memory bias towards negative events in 
chronic stress. 
Hypercortisolism (Addison's disease) 
Hypocortisolism (Cushing's syndrome) 
Physical symptoms: Apathy, fatigue, and 
depression 
Physical symptoms: Fatigue, weight gain, cold intolerance, 
dry skin 
Mental symptoms: Anxiety, irritability, poor 
concentration, agitation, emotional lability. 
Mental symptoms: Depression, mania, confusion, and 
psychotic symptoms. 
 
A diurnal variation in cortisol levels occurs in humans, with peak cortisol levels occurring around 6:007:00 AM. Hypercortisolemia with the loss of the normal diurnal variation have been reported in 
depression (especially in melancholic depression with the somatic syndrome), in some patients with 
mania (especially psychotic), obsessive-compulsive disorder and schizoaffective disorder. In PTSD 
hypocortisolemia is seen in a subgroup of patients; this may be due to aberrant feedback to the pituitary 
due to excessive glucocorticoid receptors – probably a genetic vulnerability. Low cortisol is also seen in 
chronic fatigue and fibromyalgia. 
Dexamethasone suppression test (DST) 
o Exogenous corticosteroids such as dexamethasone will suppress endogenous cortisol production if 
the HPA axis is intact. 
o In DST, 1mg dexamethasone is given at 11PM with baseline cortisol sampling; on the next day at 
8AM, 4PM and 11PM cortisol levels are measured again. If any one sample has >5mcg/L of cortisol, 
this indicates DST non-suppression. This demonstrates the failure of feedback suppression of 
ACTH/CRH and continuous production of endogenous cortisol despite administration of 
exogenous steroid (dexamethasone). 
o DST non-suppression is seen in depression and other psychiatric hyper cortisol emic states (also in 
organic hyper cortisol emic states such as Cushing’s). 
o The sensitivity of the DST for detecting major depression is modest (about 40%- 50%) but is higher 
(about 60%-70%) in very severe depression with psychotic as well as melancholic features. 
o DST non-suppression is non-specific to depression and is also seen in mania and schizoaffective 
disorder. In addition, a number of major medical conditions, pregnancy, severe weight loss and 
use of alcohol and certain other drugs (hepatic enzyme inducers that reduce dexamethasone 
availability - barbiturates, anticonvulsants, and others) can also produce DST non-suppression. 
o Despite the presence of depression, DST may suppress cortisol if the patient has Addison’s or 
hypopituitarism or taking steroids, high-dose benzodiazepines or indomethacin. 
o DST non-suppression does not increase the likelihood of antidepressant response. A negative test 
is not an indication for withholding antidepressant treatment. 
o Some data suggest that patients with DST non-suppression are less likely to respond to a placebo 
than those who show a suppression response.