This is a double-blind randomized clinical trial comparing the pain reduction of individuals treated with BTX-A and placebo as well as evaluating possible changes in neuroinflammatory biomarkers. The trial lasts 16 weeks, with a 4-week baseline phase and a 12-week randomization phase. Four visits are planned: 1) Introduction and baseline data collection, 2) Medical evaluation and treatment assignment, 3) Follow-up with biomarker analysis, and 4) Trial conclusion interview. 80 participants will be included and randomized 1:1.

Inclusion Criteria:

1. A diagnosis of classical TN or idiopathic TN according to criteria of The International Classification of Headache Disorders 3rd edition.
2. Age between 18 and 85 years.
3. Subjects must experience pain defined as a minimum of three TN related pain paroxysms per day at least four days a week of an average intensity of 4 to 10, inclusive, on the 11-point NRS (0 = no pain; 10 = maximum pain imaginable) during the last 4 weeks to enter the baseline phase.
4. During baseline phase subjects must experience pain defined as a minimum of three TN related pain paroxysms per day at least four days a week of an intensity of an average 4 to 10, inclusive, on the 11-point NRS (0= no pain; 10= maximum pain imaginable) during the last month to enter the treatment phase (to be randomized).
5. Fluency in Danish.

Exclusion Criteria:

1. Severe cardiovascular and cerebrovascular disease such as ischemic heart disease, myocardial infarction or previous stroke or transient ischemic attack, major CVD interventions during the last three months.
2. Expected poor compliance, i.e., considered unlikely to be able to complete all protocol required study visits or procedures, and/or to comply with all required study procedures to the best of the subject's and investigator's knowledge.
3. Ongoing and unstable severe psychiatric disease.
4. Anamnestic or clinical symptoms of any kind that are deemed relevant for study participation by the physician who examines the patient.
5. Change of TN treatment or treatment dose within two weeks prior to the baseline visit.
6. Previous treatment with BTX-A for facial pain.
7. Loading treatment within 4 weeks with phenytoin or sodium valproate.
8. Female subjects either pregnant, breastfeeding or with planned conception within the study period.
9. Female subject of childbearing potential who is unwilling to use an acceptable method of effective contraception during the study.
10. Known allergy to any component of BTX-A.
11. Infection at the proposed injection site.
12. Known severe neuromuscular disorders or any degree of disorder affecting the neuromuscular transmission.
13. Known comprised respiratory function.
14. Member of investigational site staff or relative of the investigator.