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4. PSYCHOPHARMACOLOGY OF DEPENDENCE FOR DIFFERENT DRUG CLASSES

Chapter 5) that is intended to render the consumption of alcohol aversive
(Kranzler, 2000). The efficacy of disulfiram is not clear, and is confounded by
the need to carefully titrate the dose, and by the need for a high degree of
compliance (Kranzler, 2000). Some people are thought to be naturally
protected from alcohol dependence because, due to a genetic alteration, they
lack a functional enzyme that metabolizes acetaldehyde (see Chapter 5) and,
therefore, have an aversive reaction (known as “flushing reaction”) when they
drink.

Sedatives and hypnotics

Introduction
Although alcohol falls under the category of sedatives and hypnotics, it has
been considered separately in this report since there is such a large body of
research on alcohol, and since its use is so prevalent. In this section, other
sedatives/hypnotics and minor tranquillizers will be discussed.
The most common minor tranquillizers are sleeping pills (benzodiazepines
and barbiturates) (Jacobs & Fehr, 1987). Many solvents produce similar effects
to sedatives/hypnotics when inhaled, but they will be considered separately
in the section on volatile solvents. The sedatives/hypnotics cause a slowing
of the functions of the brain and other parts of the nervous system.

Behavioural effects
The effects of sedatives/hypnotics range from mild sedation to general
anaesthesia, and, in the case of severe overdose, death. These drugs are
generally used for their intoxicating and inhibition-releasing properties.
Sleeping pills also become habit-forming, and tolerance readily develops to
these drugs (Jacobs & Fehr, 1987). The most common symptoms of sedative/
hypnotic use are drowsiness, mild to moderate motor incoordination, and
some clouding of mental functions (Jacobs & Fehr, 1987). These effects are
related to the role of the GABA-A receptor, discussed below. With higher doses,
these effects become more pronounced and lead to general impairment of
motor function, increased reaction times, and impairments in cognitive
function and memory. Eventually, sleep is induced in severe cases, and death
can occur from respiratory depression. Hangover effects of fatigue, headache
and nausea also occur.
Benzodiazepines and barbiturates show strong reinforcing properties in
animal models, and are self-administered by monkeys (Meisch, 2001; Munzar
et al., 2001; Gomez, Roach & Meisch, 2002) and rodents (Davis, Smith & Smith,
1987; Szostak, Finlay & Fibiger, 1987; Naruse & Asami, 1990). Benzodiazepines
have reward-consistent effects on brain self-stimulation (Carden & Coons,
1990), induce conditioned place preferences (Spyraki, Kazandjian & Varonos,
1985), and show discriminative stimulus effects (Wettstein & Gauthier, 1992).

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