If you read all the answers carefully then you will realise that there is no fundamental difference (see Manoj Suva's brief answer) between an antagonist and an inhibitor but the terms are used in different context; and different branches of Science have different preferences or traditions.

Antagonists and inhibitors are both 'chemicals' and exist for the purpose of 'blocking' or 'minimising' the outcome of a process (I tried to find a general expression - this should cover signalling and structural modifying processes) by interacting with another molecule/macromolecule. Thus, both terms describe a molecule that competes with another molecule for a binding site. This 'binding site' could be any entity that has an affinity to another relevant entity as receptors, lectins, enzymes, and also agonists.

All antagonist are inhibitors but not all the inhibitors are antagonists. Inhibitor is a broader term.

Hi Arvind!

Let's see. I think that the main common action of inhibitors and antagonists is the reduction of the stimulation of the receptor by its ligand. But, inhibitors achieve this effect by blocking specific enzymes, which are involved in signaling pathways, thus limiting the amount of ligand available for binding to the receptor. On the other hand, antagonists directly inhibit the binding of the ligand, mainly by occupying the active site.

This is about neurochemistry, which is not my field of expertise, but I hope this has given you some insight to this regard.

Erick

In my view, Inhibitors basically revert and stop the catalytic properties of any enzymes by reversible or irreversible binding with with enzymes. Antagonist are could have affinity to bind with enzymes or interacting receptor or ligands do show the negative effects in their efficacy.

Words are different though actions are same.

I think the word inhibitor is used for enzymes. Enzyme activity would be negatively regulated by inhibitor's that bind the enzyme in its active site, or other sites, or even as the enzyme/ substrate complex. Antagonists are referred to with receptor binding. There is the ligand, that naturally binds the receptor, and the antagonist blocks the ability of the ligand/ receptor complex to do what it is supposed to do. I don't think they necessarily have to bind to the same site. Maybe someone else can clarify this point. But the difference I think is mostly in hat others have already said. The nomenclature is just different for enzymes and receptors, but basically both inhibitors and antagonists block the action of the enzyme and receptor respectively.

"Antagonists" is usually used for drugs blocking a receptor on the orthosteric or allosteric binding site. The antagonist has no effects at its own (that is without the transmitter or an agonist) on constitutive activity of the receptor. If it would have effects at its own, it would be an inverse agonist. "Inhibitor" is usually used for drugs blocking an enzyme.

If you read all the answers carefully then you will realise that there is no fundamental difference (see Manoj Suva's brief answer) between an antagonist and an inhibitor but the terms are used in different context; and different branches of Science have different preferences or traditions.

Antagonists and inhibitors are both 'chemicals' and exist for the purpose of 'blocking' or 'minimising' the outcome of a process (I tried to find a general expression - this should cover signalling and structural modifying processes) by interacting with another molecule/macromolecule. Thus, both terms describe a molecule that competes with another molecule for a binding site. This 'binding site' could be any entity that has an affinity to another relevant entity as receptors, lectins, enzymes, and also agonists.

Inhibitor means inhibition. But... single target (receptor, enzyme) function is different than molecular (pathways) level. So, I think antagonist is not inhibitor until you decide what exactly you are observing. Antagonist can halt the receptor funcion but change effect in the signaling pathway in which that target has a role. There are also inverse agonists, in which case you will get promotion rather then inhibition of activation if antagonist is competitive (meaning in the same binding site along agonist).  That's my view... 

Regards

An inhibitor as I see a reaction generally stops at the root of the antagonist depends on its affinity for binding to the receptor, strength and quality of the links, or by competition and other antagonists that compete with it for connection with the receptor through which active! It is my opinion!

As a person asked me this very same question (after going through all the already available answers in this thread), I am adding the response I gave him (hoping this will help someone else):

According to me (a neuroscientist using pharmacology as a tool), an antagonist is a drug that blocks the binding, and consequently the action, of another ligand/agonist (either endogenous or not) to a specific site. This applies in my field to receptors, as the latter have a binding site for which both the endogenous ligand and the antagonist will compete. Inhibitors do not block the binding of something else to produce their effects (again, as for a neuroscientist using pharmacology as a tool); in other words they do not compete with an endogenous (or not) ligand. I would use this term with enzymes rather than receptors. The outcome of both drugs will be to inhibit or block a physiological process either by blocking the access to the agonist (in the case of an antagonist) or directly by its own action (in the case of an inhibitor). To make thinks more complex, all antagonists are not equals, some have an intrinsic effect, that is they will produce the opposite of the physiological response induced by the agonist; we refer to them as inverse agonist (as opposed to 'neutral' antagonist). In addition, some antagonist can block the access of the agonist to its binding site by acting at another site on the same receptor; that is not by competing with the binding site of the agonist. In that case, we refer to them as non-competitive rather than competitive antagonist.

I know that things can get confusing very quickly. For that reason, I provide you with the definitions that I found in the Oxford Dictionary of English (Third Edition):

- Antagonist: a substance which interferes with or inhibits the physiological action of another

- Inhibitor: a substance which slows down or prevents a particular chemical reaction or other process or which reduces the activity of a particular reactant, catalyst, or enzyme

I hope this will help.

Entedhar Sarhat: Please stop taking credit for other people's work. You continue to plagiarizer other scientists work and so far have presented several dozen responses to RG member questions as your own, but in all cases, you have copied and pasted text from other people's work, without formal citation or permission. This is dishonest and fraudulent.

For example, the plagiarized response that you pasted above was taken without permission from this linked Online Texbook: https://bio.libretexts.org/TextMaps/Map%3A_Biochemistry_Online_(Jakubowski)/06%3A_TRANSPORT_AND_KINETICS/C._Enzyme_Inhibition/C6._Agonist_and_Antagonist_of_Ligand_Binding_to_Receptors_-_An_Extension

Entedhar Sarhat: If you would like to honestly contribute, please do so by posting only formal links to the copyrighted sources, and do not post the actual articles or text here, as your own.

For those not familiar with the chronic plagiarism of Entedhar Sarhat, please take a look a his RG profile page and click on 'contributions' where you can see a list of his responses to questions ("answers") on RG. *95% of the responses were simply copied and pasted by him from other online copyrighted sources (including my own), without crediting the original authors or obtaining permission to do so.

Both antagonist and inhibitor shows their mechanism of action by blocking competetive binding of active sites of ligands/substrate molecule, but these terms should be used for specific context only.

In simple words antagonist competitively blocks receptor from binding of endogenous ligands/drugs which further ceases signal transduction pathways which are essential for intracellular biochemical reactions. it means antagonist blocks entry of message into cell from outside the cell through receptor.

Whereas enzyme inhibitors blocks binding of substrate molecules with active sites of enzyme, in this process enzyme cannot transform substrate molecule into product, which causes biological response.