Nimodipine works by slowing the movement of calcium through the muscle cells that are found in the walls of blood vessels. It does this by blocking ‘calcium channels’ in these muscle cells. Calcium is needed by muscle cells in order for them to contract, so by depriving them of calcium, nimodipine causes the muscle cells to relax. Nimodipine acts specifically on the muscle cells in the walls of arteries in the brain, causing them to relax. Nimodipine is used to improve blood flow to the brain in people who have had a type of brain bleed called a subarachnoid haemorrhage, caused by a rupture in one of the arteries on the surface of the brain.