The Agonist-To-Antagonist Spectrum of Action of Psychopharmacologic Agents

The Agonist-To-Antagonist Spectrum of Action of Psychopharmacologic Agents

Psychopharmacologic drug effect at the sites of neurotransmission is based on a spectrum of agonist to an antagonist.  An agonist is a molecule that mimics the effects of a neurotransmitter by binding and stimulating the receptor site to produce a response. Whereas, an antagonist opposes the outcome of the agonist, by blocking the action of neurotransmission. Antagonists are known as the mediators of therapeutic actions in psychiatric disorders and are the cause of undesirable side effects (Stahl, 2021). The spectrum of agonist to antagonist consists of a full agonist, partial agonist, silent antagonist, inverse agonist, and irreversible agonist. A full agonist allows the receptor to fully open the ion channel, which allows maximum signal transduction to occur; a partial agonist partially enhances signal transduction; the silent antagonist will return the receptor to a resting state; the inverse agonists goes beyond antagonism and even blocks constitutive activity; and the irreversible agonist binds and activates the receptor but the binding is permanent and the receptor is essentially destroyed (AegisShield, 2015). Where a particular psychopharmacological drug is on the agonist-to-antagonist spectrum, determines its interaction with the targeted receptor.

Compare and Contrast G Couple Proteins and Ion Gated Channels.

G couple proteins represent the most abundant family membrane proteins in the human genome, which are activated by a spectrum of structurally diverse ligands. They have seven different protein segments which span the membrane seven times and transmit signals for binding sites for neurotransmitters (Stahl, 2021).  This will allow for therapeutic drug actions to occur. Once drugs attach to these receptor sites, a full or partial blocking function of neurotransmitters occurs. The molecular changes can ultimately be affected by the drug actions, and cause changes in which phosphoproteins are activated or inactivated, or determine which enzymes, receptors, or ion channels are modified by neurotransmission (Stahl, 2021).

Ion gated channels are electrically controlled.  Unlike ions, g-Couple proteins can diffuse through the membrane and ultimately change a cell’s behavior, and ions cannot diffuse due to their charge. Ion gated channels control access in and out of neurons.  Dependent on the class of ion channels, they may be opened by neurotransmitters or voltage. Both g couple proteins and ion gated channels are types of protein receptors which are embedded in cell membranes that bind to a molecule. Medications that change the flow of ions can cause a clinical effect, unlike drugs that target g protein-linked receptor sites, which takes a more extended period to produce effect (Stahl, 2021).

How the Role of Epigenetics Contribute to Pharmacologic Action

Epigenetics is the study of how DNA interacts with the multitude of smaller molecules found within cells, which can activate and deactivate genes. Epigenetic changes are part of normal development, they can be influenced by factors including diet, chemical exposure, and medication. The resulting epigenetic changes can eventually lead to disease, for example, they turn off a gene that makes a tumor-suppressing protein, but there are classes of drugs that regulate epigenetic mechanisms to counteract disease states in humans. However, epigenetic changes are not necessarily permanent and a balanced lifestyle that includes a healthy diet, exercise, and avoiding exposure to contaminants may in the long run create a healthy epigenome.

epigenetics could explain mechanisms of human development and aging,

as well as the origins of cancer, heart disease, mental illness, addiction, and many other conditions (Guerrero-Bosagna, 2016).

The Impact of Information on How the PMHNP Prescribes Medications to Patients

To properly prescribe drugs and monitor their effect on patient, the Psychiatric Mental Health Nurse Practitioner (PMHNP) must understand concepts and mechanism of drug actions and with every client, intended use, action of drug, and side effects should be thoroughly explained. Most psychiatric medications have direct effects on the central nervous system, so it is essential to be aware of the mechanism of action of these prescribed drugs for efficacy and safety. For instance, Clozapine is an atypical antipsychotic medication prescribed for treatment-resistant schizophrenia. Patients on clozapine require close monitoring including weekly or bi-weekly lab to check for white blood cell count due to high risk for agranulocytosis, other adverse effects of clozapine include risk for myocarditis, tachycardia, constipation, orthostatic hypotension, seizure, neuroleptic malignant syndrome, anticholinergic effect, and tardive dyskinesia (MedicineNet, 2016).


AegisShield. (2015). Pharmacology Corner: Agonists and Antagonists. Retrieved from

Guerrero-Bosagna, C. (2016). What is Epigenetics? Retrieved from

MedicineNet. (2016). Schizophrenia: Symptoms, Types, Causes, Treatment. Retrieved from

Stahl Online. (2021). Stahl`s Essential Psychopharmacology. Retrieved from



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