OBJECTIVE: To investigate the influence of the quickness and duration of De Qi(or Qi arrival) on the analgesic effect of acupuncture in primary dysmenorrhea patients with a cold and dampness stagnation pattern.METHODS: Sixty-eight patients were randomly assigned to the De Qi group(deep needling with thick needles and manipulation, n = 17) or the non-De Qi group(shallow needling with thin needles and no manipulation, n = 51). Both groups underwent needling at Sanyinjiao(SP 6) for 30 min.The visual analogue scale was used to measure the degree of menstrual pain, and the Acupuncture De Qi Clinical Assessment Scale was used to assess De Qi. Only data from patients who experienced actual De Qi were included in the analysis.RESULTS: Thirty-nine patients experienced actual De Qi. Patients who experienced actual De Qi in the De Qi group(n = 14) felt De Qi more rapidly(P =0.028) and for a longer duration(P = 0.04) than patients who experienced actual De Qi in the non-De Qi group(n = 25). Both groups showed a reduction in the visual analogue scale score for pain after treatment. The analgesic effect did not significantly differ between the two groups. The occurrence time of De Qi showed a significant negative correlation with pain reduction at 20 and 30 min after needle removal(P < 0.05). There was no correlation between the duration of De Qi and the therapeutic effect.CONCLUSION: In primary dysmenorrhea patients with a cold and dampness stagnation pattern,quicker onset of De Qi when needling Sanyinjiao(SP 6) achieves a better analgesic outcome. However, a longer duration of De Qi does not affect the degree of analgesia. Compared with minimal acupuncture, active acupuncture stimulation achieves a more rapid onset and longer duration of De Qi.