Human Health and Disease · Lesson 9 of 11
Psychoactive Drugs, Alcohol and Tobacco: Biological Effects
“Opioids, cannabinoids, cocaine, other psychoactive substances, nicotine and alcohol effects on neural and organ systems.”
• Identify the major drug groups discussed and their biological targets. • Relate opioids, cannabinoids and cocaine to receptor or transporter activity. • Distinguish therapeutic use from unsafe or nonmedical use. • Explain the effects of nicotine, carbon monoxide and tobacco exposure. • Connect alcohol and other psychoactive substances to health consequences.
Psychoactive substances influence neural signalling
Psychoactive substances change the activity of the nervous system by interacting with receptors, transporters or other signalling pathways. Some are used medically because they relieve pain, reduce anxiety or have other therapeutic effects under appropriate supervision. The same substances or related compounds can be harmful when used nonmedically, without suitable safeguards, or in ways that produce impairment and dependence. A botanical origin does not establish safety: plant-derived molecules may be potent drugs with significant physiological actions. Conversely, the medical usefulness of a molecule depends on indication, dose, monitoring and benefits relative to risks.
Opioids and their receptor targets
Opioids act on specialised opioid receptors in the central nervous system and elsewhere, including the gastrointestinal tract. Receptor activation can reduce pain signalling and produce sedation, but may also depress respiration and interfere with normal functioning. Morphine is an opioid used medically as a potent analgesic in selected situations. Heroin, or diacetylmorphine, is a chemically modified derivative of morphine; morphine historically comes from the opium poppy Papaver somniferum. The relevant teaching distinction is the shared receptor system and the risk of respiratory depression, not the method by which an illicit substance is prepared.
Opioids can alter alertness, bowel function and breathing. Overdose can cause dangerous respiratory depression, particularly when opioids are combined with other sedating substances. Dependence and tolerance can develop with repeated exposure, although medical use under appropriate supervision and a substance use disorder are not identical concepts. Describing opioids only as 'depressants' is incomplete: their particular effects depend on receptor subtype, dose, route, tolerance and interactions with other medicines.
Cannabinoids and altered signalling
Cannabinoids interact with cannabinoid receptors present in neural circuits and peripheral tissues. Cannabis sativa contains multiple cannabinoids; different plant parts and preparations can contain different chemical profiles. Cannabinoid exposure can influence perception, attention, coordination, memory and cardiovascular activity, with effects varying by compound, dose and individual characteristics. Some cannabinoid-related medicines have regulated uses in particular contexts, but this does not mean that all cannabis products, methods of use or patterns of exposure carry the same evidence or safety profile.
Cocaine and dopamine transport
Cocaine is a stimulant alkaloid associated with the coca plant Erythroxylum coca. It interferes with neurotransmitter transporters, especially the dopamine transporter, resulting in increased extracellular signalling in neural pathways associated with reward and movement. This may produce stimulation and euphoria but also increases risk of agitation, cardiovascular complications and other serious effects. At high exposure levels, severe symptoms including altered perception can occur. A substance that increases perceived energy does not increase the body's overall safety or physiological reserve.
Other psychoactive medicines and hallucinogenic substances
The chapter also mentions medicines such as barbiturates, benzodiazepines and certain stimulants. They act through different neurotransmitter systems and can have legitimate clinical indications, yet misuse or use outside medical guidance can be dangerous. The flowering plants Datura and Atropa belladonna contain tropane alkaloids with anticholinergic actions; these can cause confusion, delirium and serious toxicity. Grouping every perception-altering drug together conceals major differences in receptor actions and risks. The physiology of a compound, not simply the fact that it changes consciousness, determines its potential harms.
Nicotine, tobacco smoke and carbon monoxide
Tobacco contains nicotine, which binds nicotinic acetylcholine receptors and can engage neural reward pathways and autonomic responses. Nicotine can increase heart rate and blood pressure through sympathetic signalling, including release of catecholamines. Smoking exposes the body to many additional chemicals, including carcinogens and carbon monoxide. Carbon monoxide binds haemoglobin strongly, reducing its capacity to transport oxygen and limiting oxygen delivery to tissues. These effects help explain why smoking harms the respiratory and cardiovascular systems through several distinct mechanisms.
Tobacco use is associated with increased risk of cancers of the lung, mouth and other organs, as well as chronic bronchitis, emphysema and cardiovascular disease. Smokeless tobacco also increases risks of oral and other disease. The harms arise from different chemical constituents and exposure pathways, so nicotine addiction and tobacco smoke carcinogenesis should be distinguished even while discussing them together. Avoiding exposure and obtaining appropriate support for tobacco cessation are effective health-protective measures.
Alcohol affects more than behaviour
Alcohol is a psychoactive substance that alters neuronal signalling, coordination and judgment. High levels can suppress breathing and consciousness, particularly alongside other depressant drugs. Chronic heavy exposure can damage the liver, nervous system and several other organs and can contribute to injury, heart problems and cancers. Alcohol exposure during pregnancy can interfere with fetal development. The effects depend on amount, pattern, other substances and individual vulnerability. A scientific account should distinguish acute intoxication from longer-term changes caused by repeated use.
| Substance group | Principal mechanism | Illustrative risk |
|---|---|---|
| Opioids | Opioid receptor activation | Sedation and respiratory depression |
| Cannabinoids | Cannabinoid receptor signalling | Impaired coordination and cognition |
| Cocaine | Altered monoamine reuptake | Cardiovascular and neuropsychiatric harm |
| Nicotine | Nicotinic acetylcholine receptor activation | Dependence and autonomic stimulation |
| Carbon monoxide in smoke | Strong haemoglobin binding | Reduced oxygen delivery |
| Alcohol | Multiple neural signalling effects | Impaired judgment and organ damage |
Quick Quiz
Quiz
Which receptors do opioid drugs primarily activate?
What is a major dangerous effect of opioid overdose?
Which transporter is notably affected by cocaine?
What is a major action of carbon monoxide in tobacco smoke?
What is the primary neural target of nicotine?
Which substance can cause anticholinergic poisoning in plants such as Datura?
Why is medical use of a psychoactive medicine not identical to nonmedical misuse?
Practice Problems
- Compare opioids, cannabinoids and cocaine according to their biological targets and major effects.
- Explain why tobacco exposure can increase both cancer risk and oxygen-delivery problems.
- Distinguish acute substance intoxication from chronic organ injury using alcohol as an example.
- Explain why a plant-derived drug should not automatically be considered harmless.
- Explain the distinction between therapeutic opioid use and opioid use disorder.
Opioids act primarily through opioid receptors and can relieve pain but also cause sedation and respiratory suppression. Cannabinoids act through cannabinoid receptors and can change memory, perception, coordination and cardiovascular responses. Cocaine blocks monoamine transporters, prominently affecting dopamine signalling, producing stimulation and reward-related effects but potentially dangerous cardiovascular or neurological responses. The substances do not form one mechanistically uniform group, and risks depend on exposure and individual circumstances.
Key Takeaways
• Different psychoactive substances act through different receptors and transport systems. • Opioids can relieve pain but may cause dangerous respiratory suppression. • Cannabinoids affect neural signalling, perception and coordination. • Cocaine interferes with monoamine transport and can have serious cardiovascular effects. • Nicotine activates cholinergic receptors and supports dependence. • Carbon monoxide and tobacco carcinogens cause harms through distinct mechanisms. • Alcohol may cause acute impairment and long-term organ injury. • Medical treatment and problematic nonmedical use must be distinguished.