According to the National Institute on Drug Abuse, "marijuana intoxication can cause distorted perceptions, impaired coordination, difficulty with thinking and problem solving, and problems with learning and memory. Research has shown that, in chronic users, marijuana's adverse impact on learning and memory can last for days or weeks after the acute effects of the drug wear off. As a result, someone who smokes marijuana every day may be functioning at a suboptimal intellectual level all of the time."Cocaine Use Is Decreasing According to the January to June 2012 DTI oral fluid data, the cocaine positivity rate was down 14.6% compared to 2011, continuing a downward trend from previous years; cocaine oral fluid positives in 2011 were down 10.9% compared to 2010. According to SAMHSA, in 2011, there were an estimated 1.4 million current cocaine users aged 12 or older, comprising 0.5% of the population. Amphetamines Use Continues Five-Year Upward Trend The 2012 DTI urine data further reports that amphetamines positives continue a five-year upward trend. In urine drug testing in the U.S. general workforce, the amphetamines positivity rate increased 11.7%, from 0.77% in 2011 to 0.86% from January to June 2012. In the federally mandated, safety-sensitive workforce, amphetamines positives increased 6.8%, from 0.44% in 2011 to 0.47% in the first half of 2012. The new DTI report is based on an analysis of more than 3.4 million urine and 340 thousand oral fluid drug tests performed at Quest Diagnostics laboratories between January and June 2012. About the Quest Diagnostics Drug Testing Index The Quest Diagnostics Drug Testing Index is published as a public service for government, media and industry and has been considered a benchmark for national trends since its inception in 1988. It examines positivity rates - the proportion of positive results for each drug to all such drug tests performed - among three major testing populations: federally mandated, safety-sensitive workers; the general workforce; and the combined U.S. workforce.