The investigators plan to use a statin, Simvastatin (40 mg) to improve cerebral blood flow and reduce inflammation. We have already completed a phase 11 study (n=80) which demonstrated potential benefits for acute statin therapy following SAH, and the investigators now wish to conduct a multi-centre phase 111 study to explore any potential clinical benefits in a larger population (n=1600). The purpose is to see whether the positive effects of statins seen in our phase II study translate into clinical benefits - both short term (e.g. reduced need for intensive care) and long term (outcome and wellbeing at 6 months).