Agonist vs. Antagonist Drug: Differences to Know

Several drugs present in the agonist-antagonistic class have achieved the required approval from regulatory authorities and have proven their safety in human beings. Agonist and antagonist drugs work in counteractive directions; while agonists produce actions, the antagonist works in opposite, opposing that action. These two types of drugs are known key players in pharmacology and in the human body.

Agonist and Antagonist Drugs

While drugs as a whole work many different ways within the body, addictive drugs typically work in two definitive methods of action – these two methods are classified as agonist and antagonist drugs. The defining factor between the two methods lies within how the drugs interact with the neurotransmitters.

Agonist Drugs

Agonist drugs mimic the effects of neurotransmitters naturally found in the human brain. There are two main categories of agonist drugs: direct-binding agonists and indirect-acting agonists.

Direct-binding Agonist

Indirect-acting Agonist

The first acts just like a neurotransmitter, binding directly to the receptor site – this direct bind allows the recipient to experience the effects of the drug as if they were released directly into the brain. Examples of direct-binding agonist drugs include dopamine, apomorphine, and nicotine.

Indirect-binding agonists enhance the neurotransmitter actions by stimulating neurotransmitters’ release, increasing the emissions. An example of an indirect-binding agonist is cocaine.


Antagonist Drugs

In contrast to agonist drugs which bind to the neurotransmitters in the brain, antagonist drugs do the opposite: they block the brain’s neurotransmitters. There are two main types of antagonist drugs: direct-acting antagonists and indirect-acting antagonists

Direct-acting Antagonist

Indirect-acting Antagonist

This set of antagonists work by taking up the space present on receptors otherwise occupied by neurotransmitters. The end result is that neurotransmitters themselves are blocked from binding to the receptors. The most common example of a drug belonging to this category is Atropine.

Drugs that work by inhibiting the release or production of neurotransmitters are known as indirect-acting antagonists. An example of this type of drug is Reserpine.


Differences Between Agonist vs. Antagonist Drugs

Agonist Drugs

Antagonist Drugs

Taken from a Latin word, “agnista” meaning contender.

Derived from both Greek and Latin words that signify being ‘rival, competitor or opponent.’

Aids in the production or enhancement of an action.

Opposes the action of agonist and blocks reception.

Stimulates an action

Sit idle and do nothing while agonists are working.

A response is caused when the agonists bind to the receptor site.

The response is blocked by working against the drug.

Works at the time of relaxation of muscles.

Works during the phase of muscle contraction.

Can be described as reactions or chemicals that function by changing the activity or function of receptors and helps getting bound to the receptors

They tend to manage the status-quo of the receptors by staying away from altering its activity although they might help in getting receptors bound.

Imitates the action of neurotransmitter.

The action of neurotransmitter is obstructed

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