Drug addiction involves the compulsive use of substances, often leading to harmful physical, psychological and social consequences. There is debate about whether it is a disease or a choice. It is a long-term condition, typically involving relapses after stopping.
Tolerance and Dependence
Tolerance refers to a loss of effect when taking the same dose. The person may keep increasing the dose to achieve the desired effects. Tolerance occurs with most psychoactive substances over time.
Dependence refers to a physiological and psychological need to keep using a drug. Dependence may occur due to:
- Physiological changes (notable with alcohol, opiates and benzodiazepines)
- Psychological factors (e.g., cravings and compulsions to use the drug)
Withdrawal symptoms occurs due to physiological adaptations to the drug. For example, benzodiazepines work by stimulating GABA receptors. GABA is an inhibitory neurotransmitter that has a relaxing effect. Long-term use of benzodiazepines results in the body reducing its natural production of GABA to balance the stimulating effects of the drug. When the drug is withdrawn, there is under-activity of the GABA system, causing withdrawal symptoms, such as anxiety, irritability, tremors, insomnia and even seizures.
Psychological Addiction
The brain has a reward pathway called the mesolimbic pathway. The primary neurotransmitter involved in this pathway is dopamine. The key structures involved in this pathway are the ventral tegmental area, nucleus accumbens, amygdala, and prefrontal cortex. At a very basic level, activation of this pathway by a behaviour provides pleasure and reinforces that behaviour.
Addictive substances or behaviours release dopamine within the mesolimbic pathway, providing a pleasurable reward. Repeated exposure to this stimulus reduces the number and sensitivity of the dopamine receptors in this pathway, requiring an increasingly strong stimulus (e.g., a higher dose or frequency) to produce the same reward. The response to everyday activities reduces (everyday life becomes less rewarding). As a result, the person increasingly seeks out the substance or behaviour to stimulate the reward pathway.
Cues for the substance or behaviour are embedded into the amygdala. People, events, places or objects can act as cues, triggering cravings. Stress is a common trigger, prompting the substance or behaviour as a coping mechanism.
Additionally, changes in the prefrontal cortex occur, leading to impaired function. The prefrontal cortex is responsible for executive functions such as decision-making, assessing risk, and controlling impulses.
Substances
|
Substance |
Examples |
Basic Mechanism of Action |
|
Opioids |
Heroin Morphine Oxycodone Codeine |
Stimulates opioid receptors |
|
Stimulants |
Cocaine MDMA (ecstasy) Methamphetamine |
Cocaine blocks reuptake of dopamine by the presynaptic membrane MDMA stimulates the release of serotonin and blocks its reuptake Meth stimulates the release of dopamine and blocks its reuptake |
|
Depressants |
Alcohol Benzodiazepines |
Stimulates gamma-aminobutyric acid (GABA) receptors |
|
Hallucinogens |
LSD Psilocybin |
Stimulate serotonin receptors, particularly 5-HT2A receptors |
|
Cannabinoids |
Cannabis |
Stimulates cannabinoid receptors (CB1 and CB2) |
|
Anticonvulsants |
Pregabalin Gabapentin |
Blocks voltage-gated calcium channels in the presynaptic membrane, reducing the release of excretory neurotransmitters |
|
Nicotine |
Cigarettes Vapes |
Stimulates nicotinic acetylcholine receptors |
Management
Management requires a multidisciplinary approach. Specialist drug and alcohol services are available, usually with a self-referral option. Management involves:
- Detoxification (may be coordinated at home or as an inpatient)
- Medication to help maintain abstinence
- Psychological and behavioural therapies (e.g., cognitive behavioural therapy)
- Ongoing support (e.g., a recovery coordinator and support groups)
Medication used for opioid dependence include:
- Methadone (binds to opioid receptors)
- Buprenorphine (binds to opioid receptors)
- Naltrexone (helps prevent relapse)
Medication used for nicotine dependence (smoking) include:
- Nicotine replacement therapy (e.g., patches, gum or lozenges)
- Bupropion
- Varenicline
Last updated June 2024
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