Chapter 7: Depressants and Inhalants

Depressant drugs including the barbiturates, benzodiazepines, and inhalants have many effects in common with each other and with alcohol.  As a group, they reduce the functioning of the central nervous system.  At low doses, they may be prescribed as sedatives for daytime use to reduce anxiety.  At higher doses, the same drugs may be prescribed as hypnotics to induce sleep.  Alcohol is the most widely used depressant, while benzodiazepines are the most widely prescribed depressants.

Early sedatives include chloral hydrate, also known as knockout drops or Mickey Finn, paraldehyde, and bromide salts. Barbiturates were introduced in the early twentieth century and used both as antianxiety agents and as sleep aids. Barbiturates can be grouped on the basis of the time of onset and duration of activity.  Low-dose, long-acting forms are used for daytime relief of anxiety, while higher-dose, shorter-acting forms are used to induce sleep.  Barbiturates can produce physical and psychological dependence and tolerance, and they are very dangerous when combined with alcohol due to respiratory depression.

Meprobamate and methaqualone were introduced as safer alternatives to barbiturates in the 1950s and 60s, but they, too, were linked to abuse and dependence.  Meprobamate is still available by prescription, but methaqualone is listed on Schedule I and no longer used medically.

The benzodiazepines began to be sold commercially in the 1960s; popular drugs in this family include Librium and Valium. Although they can cause dependence, the benzodiazepines are considered safer than barbiturates and are now much more widely used.  One type of benzodiazepine that has been banned is Rohypnol, which was associated with severe intoxication and used as a date-rape drug.

Both barbiturates and benzodiazepines act by enhancing the inhibitory effects of the neurotransmitter GABA.  The dosage and time course are critical in determining a drug's effects.  Overdose deaths are more likely for drugs taken in higher doses. Psychological dependence is more likely to occur with drugs that have a rapid onset of effect, while physical dependence and withdrawal symptoms are more likely to occur with drugs that have a short duration of action.

Sedative-hypnotics have several beneficial medical uses.  They are prescribed to reduce anxiety, to induce sleep, and to control seizures in people with epilepsy. Dangers of their use include dependence and toxicity.  Withdrawal from barbiturates is potentially life threatening, and there is cross-tolerance among the barbiturates, the benzodiazepines, and alcohol.  As with alcohol, sedative-hypnotics can impair judgment and coordination and increase the risk of injury during activities like driving.

High-dose exposure to inhalants causes intoxication with effects similar to depressants.  However, abuse of inhalants, especially of volatile solvents, can have very severe effects, including organ damage, neurological damage, and death by suffocation.  Most abusers of inhalants are young teens.  Products that can be abused by inhalation include readily available items like gasoline, glue, paint, lighter fluid, spray cans, nail polish, and correction fluid.

Gamma hydroxybutyric acid, known as GHB, is another central nervous system depressant.  It has powerful effects if used in high doses or combined with alcohol, and it has been used as a date-rape drug.  One form of GHB has an approved medical use for the control of cataplexy, but all other forms are listed on Schedule I.