Kratom has become a subject of concern in many countries because of the rising number of hospital visits and reports of deaths associated with its use. According to a 2016 review, "Although death has been attributed to kratom use, there is no solid evidence that kratom was the sole contributor to an individual’s death. " There is evidence that it has contributed to deaths. 15 deaths in the United States between 2014 and 2016 were kratom-related. Examples of other substances found in autopsies along with kratom have included: propylhexedrine; acetaminophen, morphine, and promethazine; temazepam, diphenhydramine, and dextromethorphan. (In this last case, levels of mitragynine were higher than those of other drugs, and there was pulmonary edema and other signs of opioid toxicity, and kratom was declared the possible cause of death). In an additional case, there were high levels of mitragynine and signs of opioid toxicity on autopsy. There were nine cases of death reported in Sweden in 2010 and 2011 relating to use of Krypton, which was kratom mixed with O-Desmethyltramadol.