What this paper adds What is already known about this subject • Pregabalin is an anticonvulsive agent prescribed as a secondary analgesic for patients when standard pain treatment is insufficient. • The analgesic effect resides to the central nervous system. • The central analgesic effect can be evaluated by electroencephalographic. What this study adds • The analgesic effect of pregabalin is reflected as a slowing of brain oscillations. • The slowing of brain oscillations for each individual patient is correlated to subjective pain scores. • The developed methodology may be used as a mechanistic approach to monitor the analgesic effect of pregabalin in pharmacological studies. SUMMARY: Aim: To identify electroencephalographic (EEG) biomarkers for the analgesic effect of pregabalin in patients with chronic visceral pain. Methods: This was a double-blind, placebo-controlled study in thirty-one patients suffering from visceral pain due to chronic pancreatitis. Patients received increasing doses of pregabalin (75mg-300mg twice a day) or matching placebo during 3 weeks of treatment. Pain scores were documented in a diary based on the visual analogue scale. In addition, brief pain inventory-short form (BPI) and quality of life questionnaires were collected prior to and after the study period. Multi-channel resting EEG was recorded before treatment onset and at the end of the study. Changes in EEG spectral indices were extracted, and individual changes were classified by a support vector machine (SVM) to discriminate the pregabalin and placebo responses. Changes in individual spectral indices and pain scores were correlated. Results: Pregabalin increased normalized intensity in low spectral indices, most prominent in the theta band (3.5-7.5Hz), difference of -3.18, 95%CI -3.57, -2.80; P = 0.03. No changes in spectral indices were seen for placebo. The maximum difference between pregabalin and placebo treated patients were seen in the parietal region, with a classification accuracy of 85.7% (P = 0.009). Individual changes in EEG indices were correlated to changes in pain diary (P = 0.04) and BPI pain composite scores (P = 0.02). Conclusions: Changes in spectral indices caused by slowing of brain oscillations were identified as a biomarker for the central analgesic effect of pregabalin. The developed methodology may provide perspectives to assess individual responses to treatment in personalized medicine.