Before patients can be prescribed something, many factors need to be considered. Are they already on drugs that could interact with a new one? Which dose is appropriate for their condition? The British National Formulary (BNF) reference book, which is published by the British Medical Association (BMA), is sent out to doctors regularly across the UK functioning as an encyclopedia of drugs, the indications and contradictions related to different drugs. The book has now launched as a free app cutting time for doctors, students and health care clinicians when they need to look up drugs before deciding what to prescribe. Now over 126,000 NHS and private healthcare clinicians are using it to treat roughly 1.5m patients every month. The app centres around an interaction checker – when clinicians open it up, they can type in the names of any drugs that the patient is already on. The app then tells the user if there are any interactions between the two.