The Toxicity of Recreational Drugs
Alcohol is more lethal than many other commonly abused substances
The easier way to learn about the relation between the quantity of a
substance taken and the resulting level of physiological impairment
is through careful laboratory study. The first example of such an
exercise, in 1927, used rodents. Research toxicologist John Trevan
published an influential paper that reported the use of more than
900 mice to assess the lethality of, among other things, cocaine. As
he and others have since found, a substance that is tolerated or
even beneficial in small quantities often has harmful effects at
higher levels. The amount of a substance that produces a beneficial
effect in 50 percent of a group of animals is called the median
effective dose. The quantity that produces mortality in 50
percent of a group of animals is termed the median lethal dose.
Laboratory tests with animals can give a general picture of the
potency of a substance, but generalizing experimental results from,
say, mice to humans is always suspect. Thus toxicologists also use
two other sources of information. The first is survey data collected
from poison-control centers, hospital emergency departments and
coroners' offices. Another consists of published clinical and
forensic reports of fatalities or near-fatalities.
But these sources, like animal studies, have their limitations.
Simply tallying the number of people who die or who show up at
emergency rooms is, by itself, meaningless because the number of
such incidents will be influenced by the total number of people
using a particular substance, something that is impossible to know.
For example, atropine is more toxic than alcohol, but more deaths
will be reported for alcohol than for atropine because so many more
people get drunk than ingest jimsonweed. Furthermore, most overdose
fatalities involve the use of two or more substances (usually
including alcohol), situations for which the overall toxicity is
largely unknown. In short: When psychoactive substances are
combined, all bets are off.
How then does one gauge the relative risks of different recreational
drugs? One way is to consider the ratio of effective dose to lethal
dose. For example, a normally healthy 70-kilogram (154-pound) adult
can achieve a relaxed affability from approximately 33 grams of
ethyl alcohol. This effective dose can come from two 12-ounce beers,
two 5-ounce glasses of wine or two 1.5-ounce shots of 80-proof
vodka. The median lethal dose for such an adult is approximately 330
grams, the quantity contained in about 20 shots of vodka. A person
who consumes that much (10 times the median effective dose), taken
within a few minutes on an empty stomach, risks a lethal reaction.
And plenty of people have died this way.
As far as toxicity goes, such deaths are quite telling. Indeed,
autopsy reports from cases of fatal overdose (whether from alcohol
or some other substance) provide key information linking death and
drug consumption. But coroners are generally hard-pressed to
determine the size of the dose because significant redistribution of
a drug often occurs after death, typically from tissues of solid
organs (such as the liver) into associated blood vessels. As a
result, blood samples may show different concentrations at different
times after death. Even if investigators had a valid way to measure
the concentration of a lethal drug in a decedent's blood, they would
still need to work backward to make a retrospective estimate of the
quantity of the drug consumed. Although the approximate time of
death is often known, the time the drug was taken and the rate at
which it was metabolized are not so easily established. Lots of
guesswork is typically involved. Obviously, people who want clean
answers should not seek information from corpses.