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 (ICA_extra), intracranial internal carotid (ICA_intra), 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 ICA_extra (15.2%) ( p ≤ 0.001). Smaller, but statistically significant, constrictions were seen in MCA (5.5%) and BA (2.1%) ( p ≤ 0.012). ICA_intra 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.