In patients with myofascial pain, painful trigger points are often treated using dry needling and local anesthetic injections. However, the therapeutic effect of these treatments has been poorly quantified, and the mechanism underlying the effect is poorly understood. In a randomized, double-blind, double-placebo clinical trial, a pressure algometer was used to measure pain-pressure thresholds in the masseter and temporalis muscles of 30 subjects aged 23 to 53 years with myofascial pain in the jaws, before and after a series of dry needling treatments, local anesthetic injections, and simulated dry needling and local anesthetic treatments (treatment group A: Procaine + simulated dry needling; treatment group B: dry needling + simulated local anesthetic; control group C: simulated local anesthetic + simulated dry needling). Subjects rated pain intensity and unpleasantness using visual analogue scales, and the data were analyzed using analysis of variance. Pain pressure thresholds increased slightly after treatment, irrespective of the treatment modality. Pain intensity and unpleasantness scores decreased significantly at the end of treatment in all groups. There were no statistically significant between-group differences in pain pressure thresholds and visual analogue scale scores at the end of treatment. The findings suggest that the general improvement in pain symptoms was the result of nonspecific, placebo-related factors rather than a true treatment effect. Thus, the therapeutic value of dry needling and Procaine in the management of myofascial pain in the jaw muscles is questionable.