How Medicines Work

#Targets and mechanisms

A medicine's mechanism is the process through which it produces an effect. Many medicines interact with targets such as receptors, enzymes or channels that control movement across cells. They may strengthen a signal, block it or alter a chemical reaction involved in symptoms or disease.

Other medicines work by replacing substances the body lacks, attacking microbes or changing immune activity. Some act mainly through physical or chemical effects, such as neutralising stomach acid. Not every medicine's mechanism is fully understood, even when studies provide evidence that it helps with a particular condition.

#An effect depends on more than the target

For many medicines, enough active substance must reach the relevant part of the body to have an effect. The route of administration and formulation influence this process. A medicine applied to the skin may act mainly nearby, while a swallowed or injected medicine may reach many tissues.

A target can also be present in healthy tissues, so changing its activity may produce unwanted effects alongside benefits. Medicines can interact with more than one target. Descriptions such as targeted or selective refer to how a treatment acts; they do not mean that it has no risks.

#Why medicines and responses differ

Medicines used for the same condition may act through different pathways. Even medicines in the same class can differ in duration, distribution, interactions and side effects. A medicine's biological action explains part of its potential, but clinical studies are needed to establish benefits and harms in people.

Responses can vary with the disease, other treatments, organ function, age and genetic differences. Some effects begin quickly, while others require gradual biological changes. A lack of immediate improvement does not by itself explain whether a medicine will help; timing and appropriate measures of response depend on the treatment.

#Common misunderstandings

A medicine’s target does not tell the whole story. Two medicines that affect the same target may differ in how long they act, where they reach in the body and what unwanted effects they cause.

A higher dose does not always produce a better result. Benefits may level off while the risk of harm continues to rise. Likewise, side effects are not proof that a medicine is working, and having no noticeable side effects does not mean it is ineffective.

Feeling better and treating the underlying condition are not always the same thing. Some medicines relieve symptoms without changing the cause; others reduce future risks without producing an obvious day-to-day change.

“Natural” does not automatically mean safe, and a familiar medicine is not suitable for every situation. Prescription medicines, non-prescription products and supplements can interact, affecting how treatments work or increasing unwanted effects.

#Questions worth asking a clinician

• What biological target or process does this medicine act on, and how does that relate to my condition?
• How does this medicine reach the affected tissue, and what limits how much gets there?
• Which healthy tissues could this medicine affect, even if it targets a specific biological process?
• What clinical evidence shows that this medicine’s biological effects lead to meaningful improvements in my condition?
• Could differences in my condition’s underlying biology make this medicine’s mechanism less effective for me?