“In fact, attempts to deter substance abuse through drug testing in prisons is actually making this gateway effect more severe. Cannabis and its breakdown products can be detected in urine for weeks, whereas heroin clears from the body much faster. Testing positive for drugs can result in an increase in sentence, so prisoners have found a way to reduce the likelihood of being caught: use heroin instead of cannabis. Far from protecting them, imprisoning cannabis users will make them more likely to start using hard drugs.”