"In the United States, there are indications of an increase in NPS use among certain user groups between 2009 and 2013; the prevalence of lifetime use of a 'novel psychoactive substance' among the population aged 12-34 was 1.2 per cent in 2013.235 There are signs of declining use of synthetic cannabinoids among secondary school students in the United States. The prevalence of past-year use of synthetic cannabinoids among twelfth-grade students decreased from 11.4 per cent in 2011 to 5.2 per cent in 2015.236 This is associated with an increase, over the same period, in the perceived risk of taking synthetic cannabinoids among the same group. The use of NPS with stimulant effects (reported as “bath salts“) among twelfth graders remained stable at 1 per cent in 2015. The prevalence of the use of synthetic cannabinoids among eighth, tenth and twelfth graders has declined to the lowest levels since the collection of such data began. However, the large amount of synthetic cannabinoids seized between 2012 and 2014 (more than 93 tons) and the large number of calls to poison centres for problems related to the use of synthetic cannabinoids (3,682 in 2014 and 7,779 in 2015)237 indicate the continued presence and use of this NPS group in the United States."