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How Medicines Work
Medicines act through different biological processes, and their effects depend on their targets, distribution and the condition being treated.
#Targets connect a medicine with a biological effect
NIGMS explains that most medicines bind to molecular targets, often proteins such as receptors or enzymes, and support or block their activity. A receptor can trigger a response when activated; an enzyme helps a chemical reaction occur. These are different ways a medicine can change a biological process.
A mechanism of action describes how an effect is produced. It is not, on its own, evidence of how much benefit a particular person will receive. This page introduces mechanisms; it does not recommend a medicine or judge an individual's treatment.
Evidence: NIGMS: how medicines work / MSD Manual: drug dynamics
#The body also changes what happens to a medicine
NIGMS distinguishes pharmacodynamics, what a medicine does to the body, from pharmacokinetics, what the body does to a medicine. Its account follows absorption, distribution, metabolism and excretion. The route and molecular properties affect how a medicine enters the blood; metabolism can inactivate some medicines or activate others.
Knowing a target is only part of the explanation. How a medicine reaches that target, how it is changed and how it leaves the body also matter. Not all medicines follow the same route, and a general account cannot supply instructions for a particular product.
Evidence: NIGMS: what is pharmacology / NIGMS: what happens to medicine in your body
#Intended and unwanted effects both need attention
NIGMS describes balancing desired effects with unwanted effects and notes that a medicine can affect sites beyond its intended target. The MSD consumer account says effects can vary with age, genetics and other conditions. FDA also describes other medicines, supplements and underlying conditions as factors in side effects.
A plausible mechanism does not make a medicine risk-free or establish that it is suitable for everyone. Ask a prescriber or pharmacist about the particular product's expected effects, warnings and instructions. Do not start, stop or change a medicine from this general explanation.
Evidence: NIGMS: how medicines work / MSD Manual: drug dynamics / FDA: learning about side effects
Source note
The sections above were checked against the linked sources. No clinical review has been performed. This is general research education, not a clinical guideline.