Pharmacology, organised the way drugs actually work
13 chapters
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about 16 min read
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free
Pharmacology looks like thousands of drug names. It is really two questions asked about every one of them. **What does the body do to the drug?** — absorption, distribution, metabolism, excretion, which together decide how much drug is at the target and for how long. **What does the drug do to the body?** — which receptor it occupies and whether it switches that receptor on or off. Every drug class below is an answer to the second question, and every dosing decision is an answer to the first. Learn the two frames and a new drug name becomes a placement problem rather than a memorisation one. This guide is educational orientation only — it is not clinical guidance, and nothing here is a basis for treating anyone.
Each chapter opens with the short version. Tap one to read the detail.
What the body does to the drug
~2 min
Absorption, distribution, metabolism and excretion decide how much drug reaches its target and for how long. Almost every practical difference between two routes or two doses traces back to one of the four.
What the drug does to the body
~2 min
Most drugs work by occupying a receptor. An agonist binds to produce the desired effect; an antagonist competes for the same site and blocks it. Adverse effects usually come from the same mechanism acting where it was not wanted.
The autonomic nervous system is the master key
~2 min
The autonomic nervous system balances sympathetic and parasympathetic activity across heart rate, breathing, digestion and secretions. An enormous fraction of drug classes work by pushing or blocking one of those two branches.
Cardiovascular drugs: pressure, rate, rhythm
~2 min
Cardiovascular pharmacology addresses a small number of levers — how hard the heart works, how much fluid it moves, how wide the vessels are, and how electrical signals propagate. Each drug class pulls one of them.
Drugs that act on clotting
~2 min
Anticoagulants, antiplatelets and thrombolytics all reduce clotting and do it at different points in the process — which is why they are monitored differently and are not interchangeable.
Anti-infectives: mechanism, then spectrum
~2 min
Antibacterials are grouped by whether they kill organisms or merely stop them multiplying, and by which cellular machinery they attack — cell wall, protein synthesis, or nucleic acids. Antifungals, antivirals and antiparasitics extend the same logic to other organisms.
Central nervous system drugs
~2 min
Sedatives, anxiolytics, antiepileptics and drugs for neurodegenerative disease mostly work by shifting the balance between the nervous system's excitatory and inhibitory signalling.
Psychotropic medication classes
~2 min
Antidepressants, antipsychotics and mood stabilisers are grouped by the neurotransmitter systems they modulate. Their defining practical feature is that effects build over weeks, unlike most of pharmacology.
Pain: opioid and non-opioid routes
~2 min
The body has its own opioid system, and opioid drugs act on those receptors to inhibit how pain signals are perceived and transmitted. Non-opioid analgesics work elsewhere, which is why combining routes achieves more than raising one dose.
Endocrine drugs replace, suppress, or mimic
~2 min
Endocrine pharmacology does three things: replace a hormone the body is not making, suppress one it is overproducing, or mimic a hormone's action for an unrelated purpose. Corticosteroids are the clearest case of the third.
Airways and gut: local targets, systemic reach
~2 min
Respiratory and gastrointestinal drugs are often delivered straight to the organ that needs them, which limits systemic exposure — but the receptors they act on exist elsewhere, so the reach is never zero.
Populations, regulation, and where this guide stops
~2 min
Dose is not a property of a drug alone — it depends on the person's organ function, body composition and stage of life. Around all of it sits a regulatory system governing how drugs are approved, labelled and monitored.
Narrow margins: cytotoxics and overdose
~2 min
Antineoplastics and overdose management share one property that dominates both: the gap between an effective amount and a harmful one is small, so dose precision and monitoring stop being administrative and become the substance of the work.
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