Low number met criteria to randomize.

This study intends to investigate the use of high-dose Vitamin D3 plus a multivitamin in the prevention of cluster headache attacks.

Participants can be enrolled anywhere in the United States that has access to one of our participating labs (for blood work - anticipated to be available in most of the USA).

The study may include:

• Screening: Participants may be interviewed, examined, fill out surveys, and get blood testing
• Week 1: baseline period (no added medications - to establish a baseline)
• Weeks 2-4: double-blinded experimental period - participants receive either 1) high-dose Vitamin D3 + multivitamin, or 2) placebo + multivitamin. Participants also fill out a survey and have blood testing.
• Weeks 5-7: open-label period - ALL participants receive high-dose Vitamin D3 + multivitamin. Participants also fill out a survey and may have blood testing.

Specifically, our primary outcome is the change from baseline to experimental weeks 1-3 in the frequency of cluster headache attacks between placebo and high-dose vitamin D. Specific primary and secondary outcomes are listed below.

Inclusion Criteria:

• A diagnosis of episodic cluster headache according to the International Classification of Headache Disorders 3rd edition as well as cluster periods that are predictable and have a duration of 6 weeks or greater and approximately one attack daily minimum OR
• A diagnosis of chronic cluster headache according to the International Classification of Headache Disorders 3rd edition as well as approximately one attack daily
• Participants who are unlikely to need to change their preventive cluster headache treatment regimen in the next 6 weeks.

Exclusion Criteria:

• Co-existing disease or other characteristic that precludes appropriate diagnosis of cluster headache.

• Active drug or alcohol use or dependence that, in the opinion of the site investigator,would interfere with adherence to study requirements.

• Inability or unwillingness of subject to give informed consent.

• Known allergy to study drug, multivitamin, or placebo components

• Pregnancy or lactation (breastfeeding)

• Usage of greater than 4,000 International Units of Vitamin D3 daily within 60 days of the beginning of the study.

• Concurrent use of Vitamin D and/or multivitamin along with the inability to stop them before the study begins.

• Liver failure or known coagulation disorder (as this study includes vitamin K) such as haemophilia, von Willebrand disease, Factor V Leiden, Antithrombin III deficiency, Protein C or S deficiency, or anti-phospholipid antibody syndrome.

• A personal medical history of more than 1 deep venous thrombosis and/or pulmonary embolism (as this study includes vitamin K).

• Current use of anticoagulants (as this study includes vitamin K). Anticoagulants include: apixaban (Eliquis), betrixaban (Bevyxxa), dabigatran (Pradaxa), dalteparin (Fragmin), edoxaban (Savaysa), enoxaparin (Lovenox), fondaparinux (Arixtra), heparin, rivaroxiban (Xarelto), and warfarin (Coumadin).

• Current use of medications that alter vitamin D metabolism, including steroids,interferon, phenytoin, phenobarbital, digitalis/digoxin, and thiazide diuretics (such as hydrochlorothiazide or chlorthalidone)

• Participants who are aware that their most recent labwork in the last 2 years showed any of the following:

  1. 25-hydroxyvitamin D levels >75 nmol/L
  2. Elevated calcium level
  3. Elevated phosphate level
  4. Abnormal parathyroid hormone levels
  5. Elevated creatinine level
  6. Of note if any values are outside the acceptable range for the study, candidates may still participate in the study if the most recent lab testing is inside the acceptable range for the study. For example, if a candididate were taking a vitamin or medication that may have caused these elevated levels, but no longer take the vitamin or medication, they may be enrolled if retesting is normal.