Extended heroin access increases heroin choices over a potent nondrug alternative
Neuropsychopharmacol. 2013-01-15; 38(7): 1209-1220
DOI: 10.1038/npp.2013.17
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Epidemiological research shows that the proportion of drug users who become
addicted to heroin is higher than to cocaine. Here we tested whether this
difference could be due to a difference in the addiction liability between the
two drugs. Addiction liability was assessed under a discrete-trials choice
procedure by measuring the proportion of rats that prefer the drug over a potent
alternative reward (ie, water sweetened with saccharin). Previous research on
choice between self-administration of i.v. cocaine or sweet water showed that the
proportion of cocaine-preferring rats remains relatively low and invariable (ie,
15%), even after extended drug access and regardless of past drug consumption
(ie, total drug use before choice testing). By contrast, the present study shows
that under similar choice conditions, the proportion of heroin-preferring rats
considerably increases with extended heroin access (6-9 h per day for several
weeks) and with past heroin consumption, from 11 to 51% at the highest past drug
consumption level. At this level, the proportion of drug-preferring rats was
about three times higher with heroin than with cocaine (51% vs 15%). This
increase in the rate of heroin preference after extended heroin access persisted
even after recovery from acute heroin withdrawal. Overall, these findings show
that choice procedures are uniquely sensitive to different drugs and suggest that
heroin is more addictive than cocaine. This higher addiction liability may
contribute to explain why more drug users become addicted to heroin than to
cocaine in epidemiological studies.