Through the potency monitoring program at the University of Mississippi supported by National Institute on Drug Abuse (NIDA), a total of 18108 samples of cannabis preparations have been analyzed over the last decade, using a validated GC/FID method.The samples are classified as sinsemilla, marijuana, ditchweed, hashish and hash oil (now referred to as cannabis concentrate). The number of samples received over the last 5 years has decreased dramatically due to the legalization of marijuana either for medical or recreational purposes in many US states. The results showed that the mean Δ 9 -THC concentration has increased dramatically over the last ten years, from 8.9% in 2008 to 17.1% in 2017. The mean Δ 9 -THC:CBD ratio also rose substantially from 23 in 2008 to 104 in 2017. There was also marked increase in the proportion of hash oil samples (concentrates) seized (0.5% to 4.7%) and their mean Δ 9 -THC concentration (6.7% to 55.7%) from 2008-2017. Other potency monitoring programs are also present in several European countries such as the Netherlands, United Kingdom, France, and Italy. These programs have also documented increases in Δ 9 -THC concentrations and Δ 9 -THC:CBD ratios in cannabis. These trends in the last decade suggest that cannabis is becoming an increasingly harmful product in the USA and Europe.