The US opioid crisis has lowered average life expectancySpencer Platt/Getty By Clare WilsonPRESCRIPTION painkillers containing opioids will soon come with a warning in the UK: “can cause addiction”. The decision, announced last month, is part of a range of measures the UK is taking in reaction to the opioid crisis gripping the US. “Being on opioids for long enough changes brain chemistry so you need more for the same effect” As medical use of these painkillers in the US has risen, so has the number of people getting hooked on them and graduating to illegal opioids such as …