Monday, September 26, 2016

Age Distribution of Legitimate and Non-Medical Opioid Use

SAMHSA (the Substance Abuse and Mental Health Services Administration) very recently released the 2015 data for its annual drug abuse survey. (The National Survey on Drug Use and Health, NSDUH.) Detailed tables here. This year’s survey, for the first time, includes questions that distinguish legitimate use of prescription drugs from misuse. Previous incarnations only asked about “illicit use.”  The survey asks the user about “Any Use in the Past Year”, “Misuse in the Past Year”, and “Misuse in the past month.” (See table 1.23A in the link above.) This is the first time I’ve ever seen an age distribution for legitimate prescription opioid users, and for all I know it's the first that's ever been published.

There are competing theories about why opioid overdoses are rising. Are the extra deaths simply coming from normal users? Or are they coming from recreational users, who may not have a legitimate medical need for them? Or are they coming from illicit users who *once* had a legal prescription but were cut off by their pain doctor? (I explore several competing explanations here.)  My hope is that I can somehow match up the age distributions of the “users” and the “deaths.” We know the age distribution of prescription opioid deaths, because we know the age of every decedent for whom opioid poisoning was mentioned on the death certificate. The CDC tracks this data, and it’s publicly available. I was curious if this distribution better overlapped the age distribution of illicit users or the age distribution of legitimate users. (Click on the chart to get the best view of it.)

The “Legitimate Use” age distribution agrees best with the “age of mortality” distribution. Legitimate users skew older, and so do the deaths. (I’m assuming here that I can subtract “misuse in past year” from “Any use in past year” to get legitimate use in past year. The “Any Use” age distribution is on there for comparison. Most use is legitimate use; there are ~97 million “any” users and 12 million “misuse” users in the past year.) On the other hand, the “misuse” distribution skews young.  At first glance, this supports the theory that the deaths are coming mostly from legitimate users. But it’s not at all conclusive.

As I mentioned in this post age is a huge risk-factor in drug-related poisonings. The disjoint between the two distributions is pretty extreme for cocaine (click the link above for details). So I could still believe that most of the deaths are coming from illicit users of legal painkillers; the age distributions don’t help answer that question. The users can skew young while the deaths skew old because older people die from drug poisonings at a much higher rate. (I’m very glad I did this previous post, otherwise I might have been misled into thinking that this was some kind of smoking gun in support of the “there are simply more legitimate users who are dying at an unchanged mortality rate” theory.)

The reason I doubt the “illicit use is driving the excess deaths” story is that prescription painkiller abuse isn’t increasing. Total illicit use and even “substance abuse disorder” (people with especially severe drug habits) are basically flat. See page 7 figure 6 and page 26 figure 36 in this document. These certainly aren’t rising enough to explain the roughly three-fold increase in opioid poisoning deaths that’s happened in the past 15 years. I don’t totally discount this explanation, but on its face it’s contradicted by the survey data.

 There are important policy implications here; I'm not just engaging in meaningless number-crunching. If the true explanation for the increase in opioid poisonings is that there are just more normal users, who are overdosing at the same rates as 15 years ago, then I don’t think there’s any cause for alarm. A treatment with a known and acceptable risk has simply been expanded into a bigger population; it shouldn’t worry us that the raw numbers increase. If the explanation is that people are getting cut off from their legal prescriptions and turning to illegal dealers and dangerous routes of administration (injecting and snorting rather than pill swallowing, or resorting to heroin), then the solution is to back off enforcement and ensure that these drugs are readily available. Don't cut these people off of their legal supply and they won't engage in the risky behaviors that are leading to so many deaths. If the explanation is that people are getting addicted to their prescription opioids and their addictions are escalating into full-blown drug abuse, then only in this third case might it make sense to crack down on prescriptions. (And it’s by no means clear that a crack-down is in order; many other criteria would need to be met first.) Hopefully coroners and medical examiners start collecting relevant information for answering this question. Did the decedent have a legal prescription at the time of death? Did they recently have a prescription? Did they have a prescription at any time, and when? Knowing this, at least for a representative sample from a few hospitals, might answer the question once and for all. I’m trying to answer the question with disparate data sets that weren’t compiled for the purpose. This approach offers suggestions, but no clear answers. 

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