Cocaine use gets more dangerous with age

Yesterday, we showed that the striking sex ratio of cocaine-specific drug-related deaths (554 male to 107 female deaths, a ratio of 5.2:1) over the decade 1998-2007 could not be explained  by a correspondingly extreme male: female ratio among cocaine users.
On the contrary, the explanation is that male cocaine-users’ risk of C-specific DRD is actually twice that of their female counterparts. The reasons for this remain unknown.
Today, we again look to successive sweeps of the British Crime Survey, but this time to estimate the risk of cocaine-related deaths by age group. Recall that there are about twice as many cocaine-related deaths as cocaine-specific deaths.
In 2001-2007, there were 168 C-related deaths (107 in 2004-2007; 61 in 2001-2003) in the youngest age group (under 25) , 484 in those between 25 and 35, and 418 in the 35+ age group – a total of 1,070 of which 526 were C-specific DRDs.
Our Table (see end of article) provides, first, the mid-year population by age-group for England and Wales in 2007 and in 2003.
By combining mid-year population estimates for England and Wales (for 2007 or 2003) with pooled information on the prevalence by age-group of those who told the BCS that they have used cocaine in the past year, we have estimated the per-annum number of past-year cocaine-users for 2004-2007 and for 2001-2003.
Using these denominators, together with the corresponding C-related DRDs, we can calculate cocaine-related death rates per 100,000 users by age-group and era. This is the sort of calculation that, back in 2000, the Advisory Council on the Misuse of Drugs had called for.
We offer up three summaries:
Sum 1 uses the recent 2008/09 sweep of BCS only in combination with mid-2007 population. This is found in the second block of the table
Sum 2 (third block of the table) is preferred. It bases its past-year cocaine-user percentages on the 2007/08+2006/07+2005/06 sweeps of BCS, according to which 3.6 per cent of 16-19 year olds reported past-year use of cocaine and 7.4 per cent of 16-24 year olds also did so. When combined with the mid-2007 population figures, these percentages suggest that, per annum during the period 2004-2007, England and Wales had around 376,000 past-year cocaine-users aged 16-24 years but 133,000 only who were over 35.  
Since there were 282 cocaine-related deaths of persons aged over 35 during 2004-2007, this implies an alarmingly high annual cocaine-related death rate of 53 per 100,000 (95 per cent CI: 47 to 59). This is seven times higher than for cocaine-users aged 16-24.  
Sum 3 (fourth block of the table) bases its past-year cocaine-user percentages on the 2004/05+2003/04 sweeps of BCS, and applies them to the mid-2003 population figures for England and Wales to estimate past-year cocaine-users by age-group. In 2001-2003, there were 136 cocaine-related deaths of persons aged 35+ years but only around 122,000 past-years’ cocaine-users, which means the cocaine related death rate for those over 35 was 37 per 100,000 per year in 2001-2003 (95 per cent CI: 31 to 43).
Whichever user count is adopted, the cocaine-related death rates clearly increase very sharply with age. For 16 to 24 year-olds, the death rate is 7 per 100,000 (CI: 6 to 9) per year in both 2001-03 and 2004-07; for those aged 25 to 35, it is 19 (CI: 16 – 22) in the earlier period and 28 (CI: 24 to 31) in the later period; and the corresponding figures for the over-35 are 37 (CI: 31 to 43) and 53 (CI: 47 to 59).
Comparing confidence intervals, a secondary finding is that cocaine’s lethality for older users (25+ years or 35+ years) has increased significantly between eras – by 40 per cent. Why we do not know. Does the impurity of cocaine or increased frequency of its use affects older users disproportionately? Alternatively, substantially higher cocaine-related deaths in older users may be linked to their age-related cardiovascular risk.
The message is plain. Older cocaine users beware!
   Table: Population and cocaine-related deaths by age group and era, per 100,000, per year


Remember our definitions: Each of 15,795 DRDs was cross-classified by era of registration (1998-2000, 2001-2003, 2004-2007), sex, age-group at death (15-24, 25-34, 35+ years), presence/absence of heroin/morphine (hereafter, H), presence/absence of methadone (M), presence/absence of cocaine (C), presence/absence of benzodiazepines (B), and presence/absence of alcohol (A).
We define cause-specific DRDs as DRDs with “one specified illegal drug present and three other specified illegal drugs absent” such as “H, not (M, C, B)” [H-specific] or “M, not (H, C, B)” [M-specific] or “C, not (H, M, B)” [C-specific]. As C-related, we define any DRD with any mention of cocaine; and similarly for H-related, M-related and B-related DRDs.

Conflicts of interest: SMB serves on, and was inaugural chair of, the Surveys, Design and Statistics Subcommittee (SDSSC) of Home Office’s Scientific Advisory Committee. In 2008, SDSSC reported on 21st Century Drugs and Statistical Science. Authors have research or clinical interests in the epidemiology and prevention of drugs-related deaths. SMB holds GSK shares and MRC-funding as part of the NIQUAD cluster on quantifying drugs harms.