Substance P is a signaling molecule that has been implicated in the pathogenesis of headache. This study aims to ascertain whether administration of substance P can induce headache in healthy adults.

Substance P is a vasoactive signaling molecule that belongs to the tachykinin family of peptides. It is expressed in multiple cells, including primary afferents of the trigeminal ganglion that innervate the meninges and its arteries. The best-known function of substance P is its role in pain transmission, and several lines of evidence has implicated substance P in the pathogenesis of headache. This study aims to ascertain whether intravenous infusion of substance P induces headache in healthy individuals who have no past or current history of primary or secondary headache disorder, except for infrequent episodic tension-type headache. For this purpose, we will conduct a randomized, double-blind, placebo-controlled, 2-way crossover trial.

Inclusion Criteria:

• Age 18 to 65 years of age upon entry into screening
• A body weight of 50 to 100 kg
• Provision of informed consent prior to initiation of any study-specific activities/procedures.

Exclusion Criteria:

• Any history of a primary or secondary headache disorder, except for infrequent episodic tensiontype headache
• Any first-degree relatives with a history of a primary headache disorder, except for infrequent episodic tension-type headache
• Any history of moderate to severe traumatic brain injury
• Any history of cardiovascular disease, including cerebrovascular diseases
• Any history of pulmonary disease
• Any other clinically significant disorders, conditions, or diseases that might impact the safety of the subject or interfere with the study's evaluation, procedures, or completion, aside from those mentioned above. This includes any relevant medical history or evidence that, in the opinion of the site investigator, might pose a risk to the subject or impact the validity of the study results
• The subject is at risk of self-harm or harm to others as evidenced by past suicidal behavior
• Female subjects of childbearing potential with a positive pregnancy test during any study visit
• Cardiovascular disease of any kind, including cerebrovascular diseases
• Hypertension (systolic blood pressure of ≥150 mmHg and/or diastolic blood pressure of ≥100 mmHg) prior to the start of infusion on the experimental day
• Hypotension (systolic blood pressure of ≤90 mmHg and/or diastolic blood pressure of ≤50 mmHg)
• Abnormalities on the electrocardiogram that, in the opinion of the site investigator, might pose a risk to the subject or impact the validity of the study results
• Daily use of any medication other than contraceptives
• Intake of any medication other than contraceptives within 48 hours of infusion start
• Intake of caffeine, nicotine, and alcohol within 12 hours of infusion start
• Headache of any intensity within 48 hours of infusion start

Anonymized data not published within this article will be made available on reasonable request from any qualified investigator.