What Is The Difference Between Agonist and Antagonist?

Agonist Vs Antagonist

Agonist and antagonist are two contradictory terms, that is, they are antonyms . These two terms also have different meanings in different fields. These concepts are found primarily in the fields of anatomy, biochemistry, and literature.

The difference between agonist and antagonist is easy to remember as they are the opposite of each other. Agonist and antagonist are English words that are self-explanatory, although they can sometimes be confusing as their spelling is somewhat similar. If there are many supporters of an issue or cause and a person opposes them, he is labeled an antagonist. Agonist is a word most often used in terms of drugs and pharmacology. It is defined as a drug that combines with receptors in the body to initiate the drug’s action. In fact, agonist and antagonist are pairs that play a huge role in the chemistry within the human body and in pharmacology, where drugs are made to act against disease. Let’s take a look at the agonist and antagonist characteristics to understand their differences.

Let’s see the Difference between Agonist and Antagonist.

Agonist vs Antagonist drugs

What is the difference between agonist and antagonist drugs?

Agonist vs Antagonist drugs in tabular form

Agonist Antagonist
Definitions Agonist drugs are drugs capable of activating receptors in the brain after binding to the receptor, resulting in the full effect of the ligand. Antagonist drugs are the drugs that bind to receptors in the brain and block the binding of ligands to the receptors, thus inhibiting the effect of the ligand.
Derived from The term Agonist is derived from the Latin word agnista, which means ‘contender’. Antagonista is derived from the Latin and Greek words antagonista and antagonistes, respectively, meaning “competitor, rival, or opponent.”
In terms of anatomy ‘Agonist’ is a muscle that is responsible for contraction in the body. “Antagonist” refers to the muscle that relaxes due to contraction of the agonist muscle.
In terms of pharmacology Agonist drugs mimic the effects of neurotransmitters in the human brain. The ‘antagonist’ drug blocks neurotransmitters in the brain.
Effects Agonist drugs stimulate action. Antagonist drugs inhibit the action.
Reply The response is caused when the agonist binds to the binding site. The response is avoided when the antagonist binds to the binding site.
Types  There are two types of agonist drugs; Direct-binding agonists and indirect-binding agonists. There are three types of antagonist drugs; Competitive antagonist drugs, Non-competitive antagonist drugs and Irreversible antagonist drugs.

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What is the difference between agonist and antagonist drugs

What is Agonist?

As mentioned above, the word agonist has different meanings. However, when we talk about the human body, the agonist is a muscle. The contraction of this muscle helps to move a part of the body directly.

In literature, the agonist is the equivalent of a protagonist. Agonist refers to the main character in a book, play, drama, etc. For example, Harry Potter is the agonist of the Harry Potter series.

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Types of Agonists

There are several types, which include endogenous, exogenous, physiological, superagonistic, complete, partial, inverse, irreversible, selective and co-agonists. Each type of agonist exhibits different characteristics and mediates distinct biological activity.

Endogenous and exogenous agonists

Endogenous agonists are internal factors that induce a biological response. Some examples of these molecules include hormones and neurotransmitters, which bind to defined receptors and induce a desired response.

In contrast, exogenous agonists are external factors that bind to various receptors and induce a biological response. An example of an exogenous agonist is a drug, such as synthetic dopamine, that binds to the dopamine receptor and triggers an endogenous dopamine-like response.

Physiological Agonists

Physiological agonists are those that can induce the same biological response; however, they do not bind to the same receptor.

An example of this type of agonist is the activation of NF-kappa B by both cytokines (Interleukin [IL]-6, IL-1, and tumor necrosis factor) and environmental stimuli (e.g., bacterial lipopolysaccharides) via cytokine signaling. associated receptors and pathogen recognition receptors, respectively.

Super Agonists

A superagonist is capable of triggering a biological response that is greater than the effect generated when the endogenous agonist binds to the receptor.

The most common form of superagonists are drugs. For example, TGN1412 is a CD28 superagonist, resulting in polyclonal T cell activation and is associated with a risk of pathogenic cytokine production if used in high doses.

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Full versus partial agonist

These are molecules capable of fully binding and activating their cognate receptor, thus inducing the complete response capable of that receptor.

In contrast, partial agonists also bind to the cognate receptor; however, they only induce a partial response. They are useful for the treatment and avoidance of drug addictions, as they induce a similar effect, although less potent and addictive.

One example is the use of buprenorphine as an alternative to opiates (eg morphine) as it only partially acts on the opioid receptor, thus reducing the likelihood of opiate dependence.

Inverse agonists

An inverse agonist binds to the same receptor as an agonist; however, it exerts the opposite biological response of an agonist. However, unlike an antagonist, rather than simply inhibiting the agonist’s response, the opposite response is induced.

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Irreversible Agonists

They are those that form a permanent association with a receptor through the formation of covalent bonds. Some of the best characterized irreversible agonists are μ-opioid receptor agonists , such as naloxazone and oxymorphazone.

Selective agonists

They are molecules specific to a particular receptor. For example, IFN-gamma is a selective agonist of the IFN-gamma receptor.


A co-agonist requires the combination of two or more agonists to induce a particular biological response. For example, the activation of infected macrophages to produce nitric oxide is dependent on the binding of bacterial ligands, IFN-gamma and TNF, to their respective receptors.

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What is Antagonist?

Antagonist also has many different meanings, just like agonist. But what’s interesting about this term is that it has the exact opposite meanings of agonist.

In anatomy, antagonist is a muscle whose action counteracts that of an agonist muscle. Agonist and antagonist muscles usually appear in pairs; when one muscle relaxes, the other contracts. Biceps and triceps are an example of this type of muscle pair.

Since the chemical agonist instigates a physiological response when combined with a receptor, the antagonist does the exact opposite; In chemistry, the antagonist inhibits or interferes with the physiological response of the agonist.

As a drug, antagonists block neurotransmitters in the brain. This contrasts with the action of agonists: mimic the effects of neurotransmitters.

As seen in all the above meanings, it is clear that agonists produce one action, or reaction, and antagonists produce its opposite action.

Antagonist has another meaning, which is perhaps the most common meaning of this word. An antagonist is a person who opposes something or is hostile to something or someone. In literature, the antagonist is the main opposing force of the protagonist.

Types of antagonist drugs

Antagonist drugs can be of three main types.

  • competitive antagonists
  • Non-competitive antagonists
  • irreversible antagonists

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Mechanism of antagonist drugs

Competitive antagonist drugs are drugs that have the ability to bind at the original binding site and inhibit the binding of the natural ligand. This is due to the shape of the antagonist which mimics the natural ligand. Increasing the ligand concentration may suppress the effect of the competitive antagonist.

Non-competitive antagonist drugs act allosterically, where they bind to a site other than the true binding site. Binding of the noncompetitive antagonist will cause a conformational change in the receptor that will inhibit binding of the true ligand.

Irreversible agonist drugs bind strongly to the receptor through covalent bonds. This will permanently modify the receptor, preventing the ligand from binding. Examples of antagonist drugs include naltrexone and naloxone. Most of the time, these drugs are used to inhibit the effects of harmful drugs like cocaine and heroin, which are agonist drugs.

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What are the similarities between agonist and antagonist drugs?

  • Both are chemical drugs that can bind to receptors in the brain.
  • Both work contractively.
  • Both can be mainly of two types – illegal drugs or prescription drugs.
  • Both are specific to receivers.
  • Both are referred to as pain relievers.
  • Both can cause harmful manifestations to health if taken in overdose.

Summary – Agonist vs Antagonist

Agonist and antagonist drugs work in a counteractive mechanism. Agonist drugs work by improving the effectiveness of natural binding to the ligand, thus regulating the effect of the ligand. On the other hand, antagonist drugs down-regulate the effect of the ligand, binding to the receptor and preventing the receptor from binding to its receptor. This is the main difference between agonistic and antagonistic drugs. Both scenarios have a pain-relieving effect and therefore act as potential analgesics. Some drugs, such as morphine, are prescribed and legal for use under medical supervision, while others are illegal for use (heroin).

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Points difference between Agonist and Antagonist?

• The agonist and antagonist pair is formed by the muscles of the human body, which are opposite each other in action. Thus, while the agonist has an action, the antagonist muscle opposes that action.

• In pharmacology, agonist and antagonist are described as agents that initiate and prevent a response, respectively.

• The agonist binds to the desired site and triggers a response of receptor cells that mimics the response of receptors to a naturally occurring substance.

• Antagonist is a chemical agent that binds to receptors and prevents a response by blocking or suppressing the response of the body’s receptors.

• Knowledge of agonist and antagonist is useful in developing new drugs to fight various diseases.

• In literature, agonist is a synonym or similar word for protagonist. Protagonist is the main character or one of the main characters of a literary work.

• Antagonist also means someone who is hostile to someone or something.

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