The Risk of Heroin Overdose

Copied from p.56 (Box 5-1) of 'Drugs and Behavior' by William A. McKim.

One of the greatest risks of being a heroin addict is death from heroin overdose. Each year about one percent of all heroin addicts in the United States die from an overdose of heroin despite having developed a fantastic tolerance to the effects of the dr ug. In a nontolerant person the estimated lethal dose of heroin may range from 200 to 500 mg, but addicts have tolerated doses as high as 1800 mg without even being sick[1]. No doubt, some overdoses are a result of mixing heroin with other drugs, but appear to result from a sudden loss of tolerance. Addicts have been killed one day by a dose that was readily tolerated the day before. An explanation for this sudden loss of tolerance has been suggested by Shepard Siegel of McMaster University, and his a ssociated, Riley Hinson, Marvin Krank, and Jane McCully.

Siegel reasoned that the tolerance to heroin was partially conditioned to the environment where the drug was normally administered. If the drug is consumed in a new setting, much of the conditioned tolerance will disappear and the addict will be more likely to overdose. To test this theory Siegel and associates ran the following experiment[2].

Rats were given daily intravenous injections for 30 days. The injections were either a dextrose placebo or heroin and they were given in either the animal colony or a different room where there was a constant white noise.

The drug and the placebo were given on alternate days and the drug condition always corresponded with a particular environment so that for some rats, the heroin was always administered in the white noise room and the placebo was always given in the colony. For other rats the heroin ways given in the colony and the placebo was always given in the white noise room. Another group of rats served as a control: these were injected in different rooms on alternate dates, but were only injected with the dextrose and had no experience with the heroin at all.

All rats were then injected with a large dose of heroin: 15.0 mg/kg. The rats in one group were given the heroin in the same room where they had previously been given heroin. (This was labeled the ST group.) The other rats, the DT group, were given the he roin in the room where they had previously been given the placebo.

Siegel found that 96 percent of the control group died, showing the lethal effect of the heroin in nontolerant animals. Rats in the DT group who receieved heroin were partially tolerant, and only 64 percent died. Only 32 percent of ST rats died, showing t hat the tolerance was even greater when the overdose test was done in the same environment where the drug previously had been administered.

Siegel suggested that one reason addicts suddenly lose their tolerance could be because they take the drug in a different or unusual environment like the rats in the DT group. Surveys of heroin addicts admitted to hospitals suffering from heroin overdose tend to support this conclusion.

Many addicts report that they had taken the near-fatal dose in an unusual circumstance or that their normal pattern was different on that day[2].

[1] Brecher, E. M., & the editors of Consumer Reports (1972). _Licit and illicit drugs_ Mount Vernon, New York: Consumers Union.

[2] Siegel, S. (1982). Drug dissociation in the nineteenth century. In F. C. Colpart & J. L. Slangen (Eds.), _Drug discrimination: Applications in CNS pharmacology (pp. 257-262). Amsterdam: Elsevier Biomedical Press.