People with methamphetamine use disorder showed differences in recognizing happy faces, interpersonal trust and punishment choices in a clinical study. The study did not demonstrate a general loss of empathy, and its laboratory findings cannot establish that a particular person is violent or untrustworthy.
Mahlberg and colleagues recruited 52 participants with methamphetamine use disorder and 51 community controls. One control was excluded for recent methamphetamine use, leaving 50 in the comparison sample. The battery tested facial emotion recognition, cognitive and emotional empathy, trust-game decisions and punishment intensity in a competitive task. Most clinical participants had severe disorder.
After adjustment for gender and education, the clinical group was less sensitive to happy expressions and more likely to classify faces retaining happy features as neutral. They also returned a lower proportion of funds in the trust task and selected more intense punishments in the competitive task. These were group-level laboratory differences, not observed criminal conduct.
Cognitive empathy did not significantly differ by group. The overall emotional-empathy group effect was also nonsignificant, as was the between-group comparison for angry-face recognition. The study therefore does not support describing every aspect of social understanding as impaired. Nor did it show that the higher punishment intensity was specifically a greater reaction to losing the previous trial.
The analysis was exploratory and not preregistered. Missing empathy data reduced the available sample, and the cross-sectional design cannot determine whether differences preceded methamphetamine use. Depression, other substance exposure and broader cognitive characteristics may contribute. Urine screening documented recent substance exposure in many clinical participants, including exposure to other drugs, but did not quantify impairment or isolate the cause of each task response. Translating these findings into a judgment about an individual requires evidence beyond membership in a diagnostic group.
See the distinction between self-report and measured functioning for a complementary study.