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Objective: This secondary analysis of a randomised controlled patient-blinded trial comparing effectiveness and side effect briefings in patients with chronic low back pain (CLBP) investigated the association between patients' pre-treatment expectations about minimal acupuncture treatment and pain intensity as outcome during and after the end of the treatment. Methods: Chronic low back pain patients with a pain intensity of at least 4 on a numeric rating scale from 0 to 10 received eight sessions of minimal acupuncture treatment over 4 weeks. The primary outcome was change in pain intensity rated on a Numerical Rating Scale (NRS 0–10) from inclusion visit to treatment session 4 and to the end of the treatment. Patients' expectations about the effectiveness of acupuncture were assessed using the Expectation for Treatment Scale (ETS) before randomization. Linear regression was applied to investigate whether patients' pre-treatment expectations predicted changes in pain intensity during and after treatment. Results: A total of 142 CLBP patients (40.1 ± 12.5 years; 65.5% female) were included in our analysis. Patients' pre-treatment expectations about acupuncture treatment were associated with changes in pain intensity after four sessions of minimal acupuncture treatment (b = -0.264, p = 0.002), but not after the end of the treatment. This association was found in females and males. Conclusions: Our results imply that higher pre-treatment expectations only lead to larger reductions in pain intensity in the initial phase of a treatment, with a similar magnitude for both females and males. As the treatment progresses in the second half of the treatment, adapted expectations or other non-specific effects might play a more important role in predicting treatment outcome. [ABSTRACT FROM AUTHOR]