Drugs of Abuse

Fundamental Pharmacological Definitions:


Scientifically, a drug is any substance—excluding essential nutrients—that alters biological processes or is specifically designed to produce a biological effect . This broad definition is refined based on clinical status and intended use:

  • Experimental and Candidate Drugs: An experimental drug is a substance that exerts a biological effect but has not yet received approval for clinical use. Once a substance enters the phase of clinical trials, it is referred to as a candidate drug.

  • Medicinal Drugs and APIs: A medicinal drug is the active component of a medicine designed to evoke a specific therapeutic effect. This is technically known as the Active Pharmaceutical Ingredient (API).

Legislative Control and Drug Scheduling:

Modern International and UK Frameworks:


Modern drug control is dictated by scheduling systems that categorise substances based on their risk to public health versus their therapeutic utility.

  • WHO Scheduling (1971 Vienna Convention):

    • Schedule I: High risk to public health with very limited or no therapeutic use.

    • Schedule IV: Lower (though still significant) risk with high therapeutic usefulness.

  • UK Legislative Framework: Controlled primarily by the Misuse of Drugs Act 1971 (MDA) and the Misuse of Drugs Regulations 2001 (MDR) .

    • Schedule 1: Includes substances with no medicinal use (e.g., LSD, MDMA, and raw opium). These require a Home Office licence for any production or possession.

    • Schedule 5: Covers low-strength preparations of certain controlled drugs that are exempt from most requirements.

The Neurobiology of Addiction:

Addiction is a complex state characterised by compulsive, repeated drug-seeking behaviour that persists regardless of adverse or dangerous consequences. Understanding addiction requires a distinction between physical and psychological states:

Key Physiological Concepts:

  • Dependence: This is the physiological or psychological need for continued exposure to a drug to avoid withdrawal symptoms .

    • Physical symptoms include tremors, sweating, and nausea.

    • Psychological symptoms involve intense cravings and dysphoria.

  • Tolerance: This occurs when a user must increase the dose to maintain the same initial biological or psychological effect.

The Brain Reward Pathway:

Most drugs of abuse share a common mechanism by hijacking the brain's natural reward circuitry, primarily the mesolimbic dopamine pathway.

  • Mechanism: Neuronal cell bodies in the Ventral Tegmental Area (VTA) project to the Nucleus Accumbens (NAc) and release dopamine (DA).

    • Functional Significance: While serotonin (5HT) is generally associated with happiness and contentment, dopamine is the primary neurotransmitter linked to pleasure and the anticipation of reward. Activities like eating palatable food, social interaction, and sex naturally activate this pathway.

Stimulants:

Stimulants act to increase central nervous system (CNS) activity, typically leading to increased alertness and reduced fatigue.

Nicotine:

Nicotine is primarily consumed through tobacco smoke or vaping and acts as a potent stimulant.

  • Mechanism of Action: It activates nicotinic acetylcholine receptors, which are ligand-gated ion channels.

  • Physiological Effects:

    • Increases peripheral adrenaline levels and enhances central neurotransmission.

    • Promotes mental alertness and hyperstimulation at low doses, though high or repeated doses can paradoxically lead to sedative effects.

  • Withdrawal: Cessation leads to significant cravings, anxiety, insomnia, and weight gain.

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Cocaine:

Cocaine is available as a hydrochloride salt (snorted or injected) or as 'crack' (a freebase form that is smoked) .

  • Mechanism of Action: It blocks the dopamine transporter (DAT), as well as transporters for noradrenaline (NET) and serotonin (SERT) . This leads to a massive accumulation of monoamines in the synaptic cleft.

  • Acute Effects and Risks:

    • Causes intense hyperstimulation, dilated pupils, and increased heart rate and blood pressure .

    • The duration of the 'high' is short: 15–30 minutes when snorted and only 5–10 minutes when smoked.

  • Long-term use can lead to paranoid psychosis and severe cardiovascular complications, including heart attacks and strokes.

Depressants:

Depressants reduce activity in the CNS, often by enhancing inhibitory neurotransmission or reducing excitatory signals.

Heroin and Opioids:

Heroin is a highly addictive opioid that is typically injected as an aqueous solution .

  • Mechanism: It activates μ\mu opioid receptors, which are G-protein coupled receptors.

    • Acute Symptoms: A rapid "rush" of euphoria is followed by "the nod"—a state of alternating wakefulness and drowsiness . It causes significant pupilloconstriction and potentially fatal respiratory depression.

  • Withdrawal: Symptoms peak at 48–72 hours and include:

    • "Cold turkey": Cold flashes accompanied by goosebumps.

    • "Kicking the habit": Involuntary kicking movements of the legs.

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Cannabis:

Cannabis contains over 100 unique chemicals, with THC being the primary psychoactive component .

  • Mechanism: Psychoactive effects are mediated through the CB1 cannabinoid receptor.

    • Physiological Effects in Humans:

      • Increased pulse rate and conjunctival reddening (red eyes).

      • Increased appetite, colloquially known as the "munchies".

  • Psychological Profile: Effects are biphasic—initial euphoria is followed by drowsiness. It can cause short-term memory impairment and depersonalisation.

  • Chronic Risks: May include respiratory disorders and a potential link to schizophrenia, particularly with adolescent exposure .

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Alcohol (Ethanol):

Alcohol is a CNS depressant, though its early effects often appear excitatory due to the disinhibition of higher brain centres.

  • Systemic Impact: Chronic abuse is highly toxic, causing:

    • Hepatotoxicity: Specifically liver cirrhosis.

    • Neuropathy: Central conditions like Wernicke’s encephalopathy (psychosis).

    • Myopathy: Primary cardiomyopathy (heart muscle disease).

  • Withdrawal Danger: Alcohol withdrawal is arguably the most dangerous of any drug of abuse, with a 15–50% mortality rate if untreated; symptoms include delirium, convulsions, and cardiovascular collapse.

Hallucinogens and Related Substances:

Hallucinogens are divided into subtypes such as psychedelics, dissociatives, and deliriants.

  • Ketamine: An open-channel blocker of the NMDA glutamate receptor. It produces a dissociative, trance-like state. High doses result in a 'K-hole'—a profound state of dissociation often accompanied by hallucinations.

  • Muscimol: Derived from the Amanita muscaria mushroom, it acts as a GABAA receptor agonist. It induces euphoria and "out-of-body" experiences.

  • MDMA (Ecstasy):

    • Mechanism: Blocks SERT and VMAT2 transporters, causing a surge in serotonin, noradrenaline, and dopamine.

    • Effects: Acts as an 'entactogen', promoting emotional openness and empathy.

    • Clinical Risks: MDMA can interfere with thermoregulation, leading to severe hyperthermia and multi-organ failure. The withdrawal "comedown" is often described as 'midweek flu'.

Public Health and Advisory Structures:

In the UK, the Advisory Council on the Misuse of Drugs (ACMD) is the independent expert body established under the 1971 Act to advise the government on drug policy. Data for monitoring drug use and deaths is primarily sourced from the Crime Survey for England & Wales (CSEW) and the Office for National Statistics (ONS).