Psychopharmacology
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Opioid-receptor antagonism increases pain and decreases pleasure in obese and non-obese individuals.
Endogenous opioids inhibit nociceptive processing and promote the experience of pleasure. It has been proposed that pain and pleasure lie at opposite ends of an affective spectrum, but the relationship between pain and pleasure and the role of opioids in mediating this relationship has not been tested. ⋯ Despite having higher levels of baseline beta-endorphin and altered beta-endorphin-reactivity to naltrexone, obese individuals reported a similar increase in pain and decrease in pleasantness following naltrexone compared to non-obese individuals. Beta-endorphin levels did not correlate with pain or pleasantness in either group, but naltrexone-induced changes in pain and pleasantness were mildly correlated. Moreover, naltrexone-induced changes in pain were related to depression scores, while naltrexone-induced changes in sweet pleasantness were related to anxiety scores, indicating that pain and pleasantness are related, but influenced by different processes.