BACKGROUND: Transcutaneous electrical nerve stimulation (TENS) is a promising non-pharmacological modality for the management ofchronic low back pain (CLBP), but its efficacy and mode of action have not been clearly established. OBJECTIVE: To evaluate the responses of plasma beta-endorphin (betaE), met-enkephalin (ME), and pain intensity (PI) among patients with CLBP exposed to TENS or sham-TENS. METHODS: This double-blind trial involved 62 participants (aged 53.29 +/- 5.07 years) randomised into TENS group (frequency 100 Hz, burst-rate 2 Hz, burst-width 150 mus, intensity 40 mA, duration 30 min), and sham-TENS group. The PI and plasma concentrations of betaE and ME were measured at baseline, immediately (0 hours), 1 hour, 24 hours, and 48 hours post-intervention. Data were analysed using general linear model repeated measures, ordinal regression, one-way analysis of variance, Kruskal-Wallis test, independent and paired t-tests, Mann-Whitney U test, Wilcoxon signed-rank test, and Kendall's tau coefficient. RESULTS: There was a significant temporal difference in PI between groups, F (1, 58) = 18.83, p < 0.001; the TENS group had better pain relief. The relative analgesic effect of TENS started immediately after the intervention (median difference (MD) -3, p < 0.001), peaked at 1 hr (MD -4, p < 0.001), and worn out by 24 hrs (MD -1, p = 0.029). However, there was no significant difference in betaE and ME between the groups from 0 hours to 24 hours post interventions, and no significant correlation between the PI, and betaE, or ME. CONCLUSION: TENS significantly reduced PI up to 24 hours after treatment.

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