Botulinum Toxin A in Frequent and Chronic Tension-type Headache

Inclusion criteria: Eligible participants must meet all of the inclusion criteria in this study. * Aged 18 to 75 years * Frequent or chronical tension type headache according to the ICHD-3 (2.2.3) criteria with 10 or more headache days per month * Headache history of minimum one year. * Previously unsatisfactory treatment effect, bothersome side-effects to or contra-indications to at least one TTH prophylactic drug. * Subject agrees to maintain current preventive headache medication regimens (no change in type, frequency, or dose) during the whole study period. * In case of women of childbearing potential (WOCBP) they have to be using highly effective contraception (for more details below). * Signed informed consent. Exclusion criteria All candidates meeting any of the exclusion criteria at baseline or visit nr.2 will be excluded from study participation: * Patients with migraine with more than 1 migraine day per month. * Patients with other forms of primary or secondary headaches; including medication overuse headache (MOH). * Change in type, dosage or dose frequency of preventive headache medication \< 1 months prior to inclusion. * Previous exposure at any time to any botulinum toxin serotype. * Pregnancy, breastfeeding or planned pregnancy. * Patients with diseases that are contraindications for use of BoNT-A (Myasthenia gravis, Eaton-Lambert syndrome, amyotrophic lateral sclerosis, other diseases interfering with neuromuscular function) or allergy to BoNT-A, or treatment with drugs affecting the neuromuscular junction; * Active infection at the sites of injection * Subject has been diagnosed with any major infectious processes such as osteomyelitis, or primary or secondary malignancies involving the face that have been active or required treatment in the past 6 months. * Any psychiatric disorder that may affect ability to comply with study procedures in the opinion of study investigator. * Other severe chronical pain conditions. * Abuse of alcohol or illicit drugs. * Participating in another trial that might affect the current study. Contraception for women of childbearing potential (WOCBP) Such methods will include combined (oestrogen and progestogen containing) hormonal contraception associated with inhibition of ovulation (oral, intravaginal or transdermal); progestogen-only hormonal contraception associated with inhibition of ovulation (oral, injectable or implantable); intrauterine device (IUD); intrauterine hormone-releasing system (IUS); bilateral tubal occlusion; vasectomised partner; sexual abstinence. This group of patients should not be using other drugs that might interact and reduce the efficacy of the used anticonceptive drug. WOCBP is defined as fertile women, following menarche and until becoming post-menopausal unless permanently sterile. Permanent sterilisation methods, include hysterectomy, bilateral salpingectomy and bilateral oophorectomy. A postmenopausal state is defined as no menses for 12 months without an alternative medical cause. Ability to understand study procedures and to comply with them for the entire length of the study. WOCBP will have to agree to take a pregnancy test before the injection with the study drug.