Substances of abuse

Alcohol affects the release of dopamine, noradrenaline and endogenous opioids, producing an activated state that is pleasurable. It specifically acts at the gamma-aminobatyric acid type A (GABA-A) receptor, thus accounting for its anxiolytic properties. At higher concentrations, alcohol also blocks glutamatergic N-methyl-D-aspartate (NMDA) receptors, resulting in amnesia and cerebral depressant effects (see Table 20.1). Ten grams of alcohol per hour will cause an increase in blood alcohol concentration levels to between 0.01% and 0.02%, with lower concentrations possible where there is marked tolerance, and higher concentrations found in females of small stature. Hazardous intake by young people tends to lead to harm as a result of behaviours associated with acute intoxication (e.g. motor vehicle accidents, assaults, drownings and suicides). Older people experience the sequelae of long-term hazardous use, such as medical complications.

TABLE 20.1 Alcohol effects

Amphetamines are a group of synthetic drugs that include ‘speed’ (amphetamine sulphate, dexamphetamine), ‘meth’ (methamphetamine or methylamphetamine) and ‘crystal meth’ (methamphetamine hydrochloride). They come in many forms (e.g. crystalline, paste, powder and pills) and in varying strengths. They are generally ingested or injected, although they can be snorted or smoked depending on what preparation they are in. They produce their stimulating effects through releasing dopamine and noradrenaline from pre-synaptic nerve terminals. Intoxication is associated with euphoria, increased physical activity, confidence, stamina and reduced need for sleep. Use that is greater than twice per week is more likely in dependent individuals. Dependence is also more likely among those who inject (50% likelihood). Long-term risks include those resulting from injecting if this is the mode of use. Teeth grinding, appetite suppression and weight loss, headache, chronic psychosis, mood instability, unpredictable behaviour and violence may also occur.

Benzodiazepines act on GABA-A receptors, resulting in anxiolytic, hypnotic, sedative and anticonvulsant effects. The duration of effects varies according to the half-life of the benzodiazepine consumed. Abuse as a component of polysubstance abuse, dependence in conjunction with alcohol or other drug dependence, and long-term dependence in the context of longstanding repeat prescriptions are the commonest problematic patterns of use. Dependence can follow 3 months of regular use, and in some instances has been noted to occur much earlier, particularly if there is already dependence on a sedating substance. Sleep impairment, sedation, cognitive impairment and falls in the elderly are some of the problems associated with dependence.

Cannabis is usually smoked, although it can be ingested. Delta-tetrahydrocannabinol (THC), the psychoactive component of the cannabis plant, binds to cannabinoid receptors (CB1) throughout the central nervous system. Intoxication is experienced within minutes of inhalation and lasts 3–4 hours. It produces transient euphoria and grandiosity, followed by sedation, lethargy, impaired short-term memory and concentration, slowed thinking, impaired judgment and motor coordination, perceptual distortions and a sense that time is passing slowly. Anxiety is a common unwanted effect. Dependence can develop. Cannabis use (especially if early onset) increases the risk of developing a psychotic disorder, as well as depression. It also impacts negatively on treatment outcomes in psychosis.

Cocaine inhibits the reuptake of noradrenaline, dopamine and serotonin. It tends to be either snorted in an intermittent binge pattern by employed individuals or injected (less frequent) by those who inject other substances. The acute effects of cocaine are largely indistinguishable from amphetamine, although its duration of action is significantly shorter. Acute and chronic use may result in a number of serious cardiac complications. Chronic cocaine use can result in psychosis, mania, depression or anxiety.

Ecstasy (N-methyl-3,4-methylenedioxy-amphetamine) is a synthetic compound that has both stimulant and hallucinogenic properties (due to its effects on noradrenaline, serotonin and possibly dopamine). Young people use ecstasy because it keeps them awake for long periods, increases sensory perception, confidence and energy levels, induces euphoria and makes them feel love, friendship and intimacy. It is usually sold as a tablet or capsule and taken orally, although some may also inject it. Young people predominantly take it in social settings in non-dependent patterns. It causes an increase in body temperature, which may, in combination with intense physical activity, a hot environment and minimal fluid intake, lead to severe heatstroke. With regular use, recurrent anxiety and panic disorders, as well as severe depression and psychotic symptoms (especially paranoid ideation), may also occur. There is evidence suggestive of neuronal damage to serotonin producing neurons after prolonged heavy use.

Hallucinogens include a variety of substances, such as lysergic acid diethylamide (LSD), phenylalkylamines (mescaline) and psilocybin (from mushrooms). The effects are highly variable depending on the user, the expectations of the user and the situation in which it is taken. The central experiences of intoxication are perceptual distortions and hallucinations, as well as depersonalisation and derealisation. Synesthesias may occur. Mood effects vary and anxiety can be prominent, reaching panic. Delusions and agitation can occur. Tolerance arises, but withdrawal syndromes have not been described. Most use is intermittent. Flashbacks are distressing perceptual disturbances reminiscent of intoxication which recur in the absence of continued use.

Heroin is a short-acting opioid that in Australia is most commonly injected. Some smoke it. First pass metabolism is extensive, so it is seldom taken orally. Unwanted effects include respiratory depression (can be fatal), pupillary constriction, nausea, vomiting and constipation. Associated hazards from use are secondary to the behaviours surrounding injecting (e.g. hepatitis C occurs in up to 15%), as well as the lifestyle associated with obtaining the substance. Approximately 30% of those who use heroin develop dependence. Heroin-dependent individuals must use two to four times per day to avoid withdrawals due to the short half-life of the drug. Morphine and slow-release morphine preparations are also abused through supplies diverted after prescription. Methadone is a longer acting opioid prescribed for opioid dependence and in chronic pain. It is also abused.

Inhalants are cheap and easily available. They comprise a wide range of household and commercial products (e.g. petrol, paint thinners, glues, solvents and spray paints). They are physically toxic, and long-term use is associated with significant neuro-cognitive disturbances. Deaths from acute inhalant use are largely associated with ‘sudden sniffing death’ (fatal ventricular arrhythmias) or accidental injury (related to impulsive risk-taking behaviour and impaired motor skills) while intoxicated. Dependence can occur.

Nicotine, the primary addictive component of tobacco, binds to nicotinic acetylcholine receptors, effecting the release of a number of neurotransmitters, including dopamine, noradrenaline and serotonin. A number of chemicals found in cigarette smoke are thought to be carcinogenic, while other chemical gases, such as carbon monoxide, impair oxygen transport in the body, or are irritants to the respiratory tract. The majority of smokers are dependent on nicotine. Those who smoke within half an hour of waking are likely to be dependent. There are much higher than expected rates of nicotine dependence in people with alcohol dependence and those with mental illnesses.

Caffeine is the most widely used substance in our community. A typical 150 mL cup of brewed coffee contains 100–150 mg of caffeine, instant coffee contains 30–100 mg of caffeine, and tea contains 30–100 mg of caffeine. Symptoms of toxicity include anxiety, insomnia, nausea and abdominal discomfort, diuresis, and elevated blood pressure and heart rate. These symptoms occur at doses above 500 mg, or more if tolerant. Dependence is common and withdrawal symptoms are most commonly headache and cognitive slowing.

Prevalence and costs

Epidemiological surveys consistently show that most people who report using substances do not do so on a regular basis (see Table 20.2). Experimental use is more common among adolescents and young people, while more frequent use is more prevalent in the 20–29-year-old age group. However, individuals with substance use disorders who present for treatment are typically older. While single episodes of use can cause problems (e.g. driving while intoxicated), individuals who use more frequently are more likely to experience deleterious mental and physical health consequences. Indeed, substance use and mental disorders frequently co-occur, and such comorbidity substantially impacts upon treatment outcomes for both conditions.

TABLE 20.2 Lifetime and recent (last 12 months) use of substances in Australia in those 14 years and over

Source: National Drug Strategy, Household Survey 2008.

Substance use and misuse are important contributors to workplace injury, loss of productivity, relationship breakdowns, violence and crime, as well as illness and disease. The cost to our society is enormous, estimated in the tens of billions of dollars, with licit drugs accounting for the bulk of the costs (56% tobacco, 27% alcohol, 15% illicit drugs). Such figures are startling, and highlight the importance of early detection and treatment.

Patterns of use

An individual’s pattern of substance use can range from experimental, through social/recreational to problem use (i.e. a substance use disorder). It is important to consider this pattern of use in addition to the quantity of substance consumed. The terms abuse and dependence are used to describe patterns of problem use (see Table 20.3); dependence is generally regarded as the more reliable, robust and useful construct.

TABLE 20.3 DSM–IVTR criteria for abuse and dependence (synopsis)