What Is Mechanism of Action?

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The term "mechanism of action" is a pharmacological term commonly used when discussing medications or drugs. It refers to how the drug works on a molecular level in the body. The term "mode of action," on the other hand, is sometimes used to describe the more general response or effect of the drug, such as what a person feels when they take the medication.

Mechanism of action and mode of action are sometimes used interchangeably, though the latter can be used in more general terms.

Here is what it means if your healthcare provider uses the terms mechanism of action or mode of action when discussing your treatment, as well as examples of how the terms can be applied to medical and mental health conditions.

Person with a pill in their hand
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Definition

Healthcare providers, such as doctors, pharmacists, and psychiatrists, often use the term mechanism of action when they are talking about medication. If you are talking to a healthcare provider about a drug you have been prescribed, they will likely start by explaining what the medication is supposed to do.

Mechanism of action refers to the biochemical process through which a drug produces its effect.

For example, if you have a bacterial infection, your doctor might say that you need an antibiotic. They may explain that they are prescribing a specific antibiotic for you because it is very good at targeting the specific bacteria that are making you sick.

How Mechanism of Action Is Determined

Using the antibiotic example, when scientists are researching antibiotic treatments in the lab, they can see how effective different medications are at fighting specific bacteria. They study the cells closely and watch how they interact. Their observations reveal how the drug attacks and kills the bacteria.

When they discuss the exact way that a drug works on its target, they refer to it as the medication's mechanism of action.

Drugs bind to receptors that are located on the surface of cells or within the cytoplasm (a jelly-like substance inside a cell). After the receptors bind to a cell, the drug will take on one of two roles: agonist or antagonist.

Agonists vs. Antagonists

Drugs that are agonists activate the receptors they bind to. This bond will either increase or decrease the activity within the cell. Antagonist drugs do the opposite; they will block the receptors and prevent the natural agonists within the body from binding.

Most drugs bind to a specific type of receptor (which is known as receptor selectivity). The ability of a drug to bind to a certain receptor is determined by its unique chemical structure.

Examples 

When a person takes a medication to treat a condition, the mechanism of action is the specific biological process through which the drug treats the underlying issue and/or reduces symptoms. Sometimes the mechanism of action of a drug is known—other times, it's not fully understood.

For example, the mechanism of action of selective serotonin reuptake inhibitors (SSRIs) is well known. SSRIs inhibit the reuptake of serotonin in the brain, which allows the levels of the neurotransmitter to increase. Having more serotonin can help alleviate symptoms of depression and improve a person's mood.

Sometimes, a medication's mechanism of action is unknown. Scientists can see and measure that a drug is working, but they don't yet know how it does. For example, lithium (a mood stabilizer used to treat bipolar disorder) demonstrates a clear effect on symptoms, but the biological process by which it exerts this effect is not entirely clear.

Some drugs have more than one known mechanism of action. Caffeine has been observed to affect more than one receptor in the brain, which produces effects in multiple body systems. For example, drinking a cup of coffee might increase your heart rate and also stimulate intestinal contractions.

Other Uses

The terms mechanism of action and mode of action are occasionally also used to describe non-drug treatments, particularly when discussing mental health disorders.

For example, when describing a psychosocial intervention such as psychotherapy, the mechanism of action would be the specific intervention that produces a change in a person's symptoms. However, these interventions are complex and usually rely on multiple mechanisms from both the person in therapy and the therapist.

A Word From Verywell

Understanding what mechanism of action means when talking to your healthcare provider about your medical or mental health treatment can help you conceptualize how the medication or therapy could support your recovery and you feel better.

If you have questions about the mechanism of action for a drug or treatment your doctor has recommended, ask for clarification. The concept can be a bit challenging to explain, but it's important that you have a clear understanding of how the treatment you have been given is intended to work, as well as what signs to look for that could suggest it's not the most effective option for you.

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