Acceptance and Commitment Therapy vs Medical Treatment as Usual Wait-list Control for Primary Headache Sufferers

Participants will be randomly assigned to one of the two groups: ACT-based intervention, plus their usual health care or Medical Treatment as Usual only (MTAU). The MTAU group will follow their usual medical treatment (prescribed headache medication). Treatment sessions will be conducted weekly by two co-therapists in groups of approximately 8-10 participants for 1 ½ hour. The control group will receive the ACT intervention following the completion of the 3-months follow-up assessment of the treatment group. Participants in both groups will complete primary and secondary outcome scales, as well as ACT process effects scales at pre, post and 3-months follow-up. The treatment group only will be also assessed at 6 and 12-months follow-up. The ACT protocol and the patients' workbook were developed for the needs of the Algea project (Vasiliou \& Karekla, 2015). Techniques will focus on key ACT processes aiming at promoting psychological flexibility for the head pain experience.

Participants in the Waitlist control+ MTAU will not receive any active intervention. Upon completion of the 3 months follow-up assessment of the ACT+MTAU group, participants allocated in the Waitlist control+MTAU will receive the ACT intervention.