New opiate and crack-cocaine users: characteristics and trends 10 
 
before 1960 was removed and because DIP tests are only administered to those aged 18 and 
over, so only using data to 2013 means it would not be possible for anyone to be born in 1996 
or afterwards to be included. Even so, it is clear from the year-of-birth distribution (Figure 2) that 
positive opiate tests drop off sharply for those born after 1982. This is in line with other evidence 
suggesting that the number of new users of opiates decreased sharply in the 2000s. This needs 
to be considered when interpreting the analysis that follows. When DIP and the NDTMS 
treatment system began in the mid-2000s, there already existed a cohort of around 320,000 
OCUs, according to available estimates by Hay et al., (2013). And most of these individuals 
began using opiates/crack during the epidemic years of the 1980s and 1990s. In terms of data 
capture this means it is hard to separate the gradual inclusion of more and more individuals 
from this original cohort from genuinely new users of these drugs. 
Figure 2: Year of birth distribution for all opiate-only/positive-for-both tests. 
 
Figure 3, which shows the age of the individual at a positive test, also reveals that although the 
average age at positive test is 32, the peak is quite flat, with high numbers of positive tests still 
being recorded by individuals in their late 30s and even into their 40s.