Side effects of paracetamol an allergic reaction, which can cause a rash and swelling. flushing, low blood pressure and a fast heartbeat – this can sometimes happen when paracetamol is given in hospital into a vein in your arm . The maximum 24-hour dose of paracetamol is 4g, but as little as 5g can cause liver complications, and it can be easy to overdose accidentally by taking more than one product containing it at the same time