Mendes et al retrospectively reports 21 independent treatments of propofol in 18 patients suffering primary and secondary chronic daily headache over a 1 year period 23 Subanesthetic doses of propofol were administered by intermittent intravenous boluses 20 - 30mg every 3 to 5 minutes (range 60 - 380 mg). 6 patients reported complete relief of pain with the treatment, 1 patient had no pain relief; on average patients reported a 58.92% decrease in pain using a 0 - 10 scale. It is reported that 8 patients' headache cycles were broken when followed up several days later but no information is available on the longer term impact of these interventions. In these two studies there appears to have been good tolerance of propofol and no significant adverse events.