New opiate and crack-cocaine users: characteristics and trends 14 
 
Figure 5: Year of birth for all individuals on their first positive test (opiates-only or positive-
for-both.) 
 
Figure 6:  Age at first positive test (opiates-only or positive-for-both.) 
 
Note: as a guide to the OCU population, this chart is left-truncated as DIP tests are not given to under-18s.