***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Essential hypertension is characterised by reduced pain sensitivity . Hypertensive hypoalgesia has been attributed to elevated endogenous opioids and /or increased activation of descending pain modulation systems . A double-blind placebo-controlled design compared the effects of naltrexone and placebo on cold and ischemic pain in unmedicated newly-diagnosed patients with essential hypertension . Patients performed a cold pressor task while resting and while performing a distracting secondary task . They also performed a forearm ischemia task while resting . Although the cold pressor and ischemia tasks elicited significant increases in pain and blood pressure , pain ratings and pressor responses did not differ between naltrexone and placebo .  Cold pain was reduced by distraction compared to rest . The finding that opioid blockade with naltrexone did not moderate the pain and pressor responses to cold and ischemia suggests that pain and associated blood pressure responses are not modulated by opioids in hypertension . The finding that the distracting secondary task successfully reduced pain ratings suggests normal supraspinal pain modulation in essential hypertension Although non-suicidal self-injury ( NSSI ) involves self-inflicted physical harm , many self-injurers report feeling little or no pain during the act . Here we test : ( 1 ) whether the pain analgesia effects observed among adult self-injurers are also present among adolescents , and ( 2 ) three potential explanatory models proposing that habituation , dissociation , and /or self-criticism help explain the association between NSSI and pain analgesia among adolescents . Participants were 79 adolescents ( 12 - 19 years ) recruited from the community who took part in a laboratory-based pain study .  Results revealed that adolescent self-injurers have a higher pain threshold and greater pain endurance than non-injurers . Statistical mediation models revealed that the habituation and dissociation models were not supported ; however , a self-critical style does mediate the association between NSSI and pain analgesia . The present findings extend earlier work by highlighting that a self-critical style may help to explain why self-injurers exhibit pain analgesia . Specifically , the tendency to experience self-critical thoughts in response to stressful events may represent a third variable that increases the likelihood of both NSSI and pain analgesia . Prospect i ve experimental studies are needed to replicate and tease apart the direction of these associations , and may provide valuable leads in the development of effective treatments for this dangerous behavior problem BACKGROUND Non-suicidal self-injury ( NSSI ) has received increased attention in the mental health literature and has been proposed as a diagnostic entity for DSM-5 . However , data on NSSI in the United States adult population are lacking . METHOD The prevalence and nature of NSSI were examined in a r and om-digit dialing sample of 439 adults in the United States . Participants were recruited during July and August of 2008 . RESULTS Lifetime prevalence of NSSI was 5.9 % , including 2.7 % who had self-injured five or more times . The 12-month prevalence was 0.9 % . Methods of NSSI reported included cutting/carving , burning , biting , scraping/scratching skin , hitting , interfering with wound healing and skin picking . Half of self-injurers reported multiple methods . The average age of onset was 16 years ( median 14 years ) . Instances of NSSI infrequently co-occurred with suicidal thoughts and with use of alcohol or drugs and rarely required medical treatment . Most injurers reported that NSSI functioned to alleviate negative emotions . Fewer reported that they self-injured to punish themselves , to communicate with others/get attention or to escape a situation or responsibility . NSSI was associated with younger age , being unmarried and a history of mental health treatment , but not with gender , ethnicity , educational history or household income . CONCLUSIONS Results are largely consistent with previous research in adolescent and young adult sample s. Study limitations notwithst and ing , this study provides the most definitive and detailed information to date regarding the prevalence and characteristics of NSSI in US adults . In the future , it will be important for large-scale epidemiological studies of psychopathology to include questions about NSSI Although theoretical and clinical literature emphasize the role of both an unwillingness to experience emotional distress and physical pain tolerance in deliberate self-harm ( DSH ) , research on their associations with DSH remains limited . This study sought to examine the relationships between DSH and the willingness to experience emotional distress and tolerate physical pain , including the moderating role of interpersonal distress in these relationships . To this end , young adults with recent DSH ( n = 43 ) and controls without any DSH ( n = 52 ) were r and omly assigned to 1 of 2 emotion-induction conditions ( distressing or neutral ) , after which behavioral measures of both the willingness to experience distress and physical pain tolerance were obtained . Consistent with hypotheses , findings indicated heightened physical pain tolerance among self-harming individuals only under conditions of interpersonal distress . Furthermore , findings provided some support for the hypothesized association between DSH and the unwillingness to experience emotional distress , suggesting that self-harming women evidence less willingness to experience emotional distress only under conditions of depleted regulatory capacity ( eg , following an interpersonal stressor ) We report the effects of the opiate antagonist naloxone on pain and mood change associated with the cold pressor test in self-injurious borderline 
    Output:
    
The review found a lack of substantive focus on psychological correlates of altered pain tolerance in this population .
The evidence suggests that there is elevated pain tolerance among those who engage in NSSI .