To summarise, an antagonist is an obstacle.
A drug may bind to a receptor that normally responds to a natural chemical in the body. If the drug binds to that receptor but does not activate it, then the natural chemical may not be able to exert its full effect. “This is one way in which drugs can reduce or control certain biological reactions.
It is paired often with an agonist which takes the opposite action, activating a receptor and eliciting a response, while an antagonist prevents activation.
The mechanics of an antagonist
The antagonist’s action depends on the type of antagonist, and the receptor or biological target.
Most antagonists act through binding to a site on a receptor. The bound antagonist can prevent another molecule binding to that site. The antagonist can’t elicit the same receptor response, an agonist can. The main action is to prevent, decrease or inhibit activation.
An easy example is the interaction of the receptor with its natural signalling molecule. You can picture the receptor as a lock and the natural molecule as the key that fits it. An antagonist can have the lock but not turn it around. The normal key may have less chance to turn on the receptor while it is there.
This interaction does not always happen the same way. Some antagonists bind to the same location as an agonist, others bind to a different part of the receptor and alter the response of the receptor.
Receptor antagonist – What is it?
A receptor antagonist is a compound which binds to a receptor and blocks or decreases activation by an agonist.
Binding may be reversible or, in some cases, functionally irreversible.
This drug could be removed from the receptor by a reversible antagonist. Then another molecule may bind to the receptor and activate it. Factors such as the strength of binding of the antagonist and the amount of the antagonist can affect the intensity and duration of the blocking effect.
An irreversible antagonist binds very strongly to its target. In some cases can mean that the affected receptor is not available until the body makes new receptors or until the receptor function is otherwise restored.
Read the full explanation
Antagonists, competitive and non-competitive
Antagonists are often categorised according to the ways they prevent receptor activation.
A competitive antagonist competes with an agonist for the same receptor binding site. If there are more antagonists present, it could create complications for the agonist. The degree of effectiveness is likely to vary based on the concentrations of both substances and their capacities for binding to the receptor.
The mechanism of action of a non-competitive antagonist is different; it may attach to another site on the receptor or affect the receptor in such a way that increasing the amount of agonists will not lead to overcoming the antagonist’s effects.
There are also antagonists which have more complex mechanisms of action, so these two categories are not exhaustive all interactions.
Antagonist versus agonist
The easiest way to look at the difference is to think about what happens once the substance has reached its receptor.
An agonist is a molecule that binds to a receptor and activates that receptor, leading to a biological response. An antagonist attaches to the receptor, or some other appropriate target, but prevents or reduces the response.
For example, if a receptor normally increases a physiological activity when a signalling molecule binds, an agonist might produce or increase the activity. An antagonist may block the receptor from being activated by the signalling molecule and so reduce the response.
This difference is important in understanding how drugs work. Two drugs may act on the same receptor but have very different effects since one may activate the receptor while the other blocks it.
Why do we use antagonists in medicine?
In some cases blocking a receptor may be useful when you need to reduce a specific biological response.
Some drugs block receptors that are involved in pain, blood pressure, allergies, heart function and other physiological processes. But the goal is not always to completely block a biological pathway. It’s often to diminish the inappropriate or excessive response.
For example, some medicines that treat allergic symptoms work by blocking histamine receptors. Histamine is implicated in symptoms such as itching, sneezing and a runny nose. These medicines can help to reduce these symptoms. They work by blocking the action of histamine at, certain receptors.
Other receptor antagonists are used for entirely unique purposes. In pharmacology, an antagonist is a drug that binds to a specific, receptor and blocks the action of another drug or substance.
In pharmacology an “antagonist” is a substance which blocks or dampens the action of another at a given, biological target. The most common way this occurs is receptor binding.
It’s worth remembering that an antagonist does not necessarily make a substance disappear from the body. That substance, when it arrives at the target, alters the outcome.
The effect may also vary between drugs. For example, an antagonist may have a greater effect on one receptor subtype than another. Such selectivity may influence both its intended actions and the chance of adverse effects.
Dosage is important too. At low concentration a few of the receptors may be blocked, but as the concentration is increased, an increasing number of the available receptors become occupied. The overall response can also be affected by the speed at which the drug gets to its target and its duration there.
Antagonist action examples
A common example is a beta blocker which can function as an antagonist at beta-adrenergic receptors. These block substances such as adrenaline from attaching to these receptors. This can affect things such as heart rate and heart activity.
Another example is a histamine H1 receptor antagonist, better known as an antihistamine. These medicines block the effects of histamine at H1 receptors and are widely used for allergy symptoms.
There are many other types of antagonists, and you cannot assume their effects from the word alone. All important: the particular receptor, mechanism of action, dose and clinical use.”
Meaning of ‘Antagonist’ in simple terms
An antagonist is basically a blocker. It attaches itself to a biological target and stops another substance from having its usual effect, or lessens that effect.
The term is particular useful in pharmacology, as it describes a particular type of drug action. Understanding antagonists also makes it easier to understand related terms such as agonist, receptor, affinity and receptor activation.
The conclusion is simple: an agonist activates a receptor, while an antagonist blocks or reduces that activation.
Research Use Only. This glossary explains terminology used in published research. It is not medical advice and does not describe any product for human or animal use.