[davekm (OP)]

I've looked at some studies on this subject:

Increase cortisol

3.5 mg/kg caffeine potentiated stress-related increases in plasma epinephrine and cortisol stress, more than doubling the responses observed in the control condition. (average intake 500mg)
225 mg daily also increased cortisol response to a task.
300mg daily causes reduced, but not eliminated response.
260 mg increased cortisol and adrenocorticotropic hormone in chronic users

No effect

75 -150mg had no effect on salivary cortisol levels in 12 hr withdrawn (100-500 average intake)
250mg & 500mg no changes in hormones (150-450)
chronic 100mg no effect
300mg no difference students (200-700)

What am to conclude from this? Does this mean caffeine raises cortisol throughout the working day? I myself only take in 150mg per day.