Aim To explore a possible differential effect of sumatriptan on extracerebral versus cerebral arteries, we examined the superficial temporal (STA), middle meningeal (MMA), extracranial internal carotid (ICAextra), intracranial internal carotid (ICAintra), middle cerebral (MCA) and basilar arteries (BA). Methods The arterial circumferences were recorded blindly using high-resolution magnetic resonance angiography before and after subcutaneous sumatriptan injection (6 mg) in 18 healthy volunteers. Results We found significant constrictions of MMA (16.5%), STA (16.4%) and ICAextra (15.2%) ( p ≤ 0.001). Smaller, but statistically significant, constrictions were seen in MCA (5.5%) and BA (2.1%) ( p ≤ 0.012). ICAintra change 1.8% was not significant ( p = 0.179). The constriction of cerebral arteries was significantly smaller than the constriction of extracerebral arteries ( p < 0.000001). Conclusion Sumatriptan constricts extracerebral arteries more than cerebral arteries. We suggest that sumatriptan may exert its anti-migraine action outside of the blood–brain barrier.