Figure 4. Mean plasma (A) and salivary cortisol (B), adrenocorticotropic hormone (ACTH; C), and beta-endorphin (D) concentrations obtained before and after consuming placebo or naltrexone and after performing the cold pressor test (CPT) and thermal pain test. Order of the 2 pain procedures was counterbalanced. Because of similar changes in men and women, data were collapsed across gender.