ACT consists in 6 weekly sessions, 90 minutes each, and 2 supplementary "booster" sessions, at two and four weeks after the conclusion of the weekly session. The main focus of the six ACT session will be the following: 1) Creative helplessness: the problem of control; 2) Indentifying values: introduction to Mindfulness; 3) Actions guided by values: working with thought; 4) Working with Acceptance and Willingness; 5) Committed Actions: self-as-context; 6) Integration: working with obstacles - wrap-up. The booster session starts with a mindfulness exercise, followed by a review of the contents covered across the ACT program.

Patients will be trained in small groups (5-7 patients each) and guided by a specifically trained therapist. They will be educated to practice at home according to the instructions given by the therapist during the sessions.

Pharmacological prophylaxis will be prescribed based on patients' profile (e.g. previous failures or contraindications), and limited to Topiramate, Propanolol, Amytriptiline or Flunarizine. Doses will depend on patients' features, and the doses herein reported are to be intended as approximate ones: Topiramate at the dose of 50mg/day; Propanolol at the dose of 20mg/day; Amytriptiline at the dose of 10mg/day; Flunarizine at the dose of 5mg/day.

The Migraine Disability Assessment measures the impact of migraine headaches in terms of entirely missed workdays, partially missed workdays, entirely missed homework days, partially missed homework days and days with missed leisure/family activities. The score ranges between 0 and 270, with higher scores indicating higher disability; a score >=21 indicates presence of relevant disability.

The 6-item Headache Impact Test measures the impact of headaches on patients' ability to function on the job, at school, at home and in social situations. It is composed of six items, which are rated on a six-level scores (never, rarely, sometimes, very often, always, which are respectively assigned a score of 6, 8, 10, 11, 13). The total score is given by the sum of single items score and ranges between 36 and 78, with higher scores indicating worse impact. A total score below 46 indicates no impact; score in the range 50-55 indicates minor impact; score in the range 56-59 indicates substantial impact; score equal or higher than 60 indicate severe impact.

The Hospital Anxiety and Depression Scale has two separate score for depression and anxiety, each composed of seven items that are rated 0-3. Both anxiety and depression sub-scores are defined as the sum to the response to item and range between 0 and 21, with higher scores indicating worse anxiety and depression problems. A score >=8 is the cut-off for both anxiety and depression caseness.

The Allodynia Symptom Checklist is composed of 12 items referring to the presence of allodynia, i.e. the clinical situation in which skin stimulation that ordinarily would not produce pain (e.g. wearing eyeglasses) is experienced as pain in the course of headache. Each item is rated on a 0-2 scale, and therefore the total checklist score is 0-24, with higher score indicating worse allodynia. Total score in the range 0-2 indicate no allodynia, those in the range 3-5 indicate mild allodynia, those in the range 6-8 indicate moderate allodynia and those >= 9 indicate severe allodynia.

The Pain Catastrophizing Scale is composed of 13 items, that have to be rated between 0 and 4. The total score is given by the sum of the response to the items and therefore ranges between 0 and 52, with higher scores indicating higher tendency to catastrophizing, and a score >= 30 indicates clinically relevant level of catastrophizing.

The Acceptance & Action Questionnaire-2 is composed of seven items addressing psychological inflexibility, each item ranges between 1 and 7, with higher scores indicating greater levels of inflexibility. The questionnaire score ranges between 7 and 49, and a score of 24 is a proposed cut-off.

The Chronic Pain Acceptance Questionnaire is a measure of acceptance and experiential avoidance, defined in terms of the person's ability to participate daily activities while acknowledging the presence of pain, and to allow the experience of pain with no efforts to avoid or control it. It is composed of 20 items rated between 0 and 6, and the questionnaire total score is given by the sum to each of them. Score ranges between 0 and 120, with higher scores indicating higher capacity to engage in activities with presence of pain and with no attempts to avoid or control it.

The scale measures people's tendency to be mindful of moment to moment experience, i.e. it focuses on the presence of attention and awareness of what occurs in the present. It is composed of 15 items, rated on a 1-6 scale: thus overall score ranges between 15 and 90, with higher scores reflecting higher mindfulness (i.e. higher attention and awareness of what occurs in the present).

Work productivity reduction is a composite measure given by two sub-dimension, namely absenteeism and presenteeism. Absenteeism is calculated as the number of days in which the person did not get to work because of headache. Presenteeism is calculated as the number of days in which the person was at work, but worked with reduced efficiency due to the presence of migraine headache. To calculate presenteeism, patients have to refer the number of days in which they worked with lower ability due to headache, and have to provide an estimate of their average performance level on a 1-99% scale. The portion needed to reach 100% performance is the productivity reduction coefficient, which is multiplied by the number of days with presenteeism to get the overall presenteeism measure.

The overall work productivity reduction is given by the sum of absenteeism and presenteeism.

Proportion of patients meeting the criteria for Chronic Migraine and Medication Overuse Headache (1.3 and 8.2 of the ICHD-3beta).