Serotonin (5-hydroxytryptamine, 5-HT) is an important biogenic amine neurotransmitter involved in regulating mood, cognition, sleep, sensory processing, and various physiological activities. Its effects are mediated not by a single receptor, but by multiple receptor subtypes and their distinct intracellular signaling mechanisms. The 5-HT2A receptor has become an important subject in neuropharmacology and drug development because of its role in cortical neuronal activity and its association with antipsychotic drugs, psychedelic compounds, and emerging therapeutic strategies for neuropsychiatric disorders [1,2].
1. The Serotonin Receptor Family: How Do Different Subtypes Transmit Signals?
The serotonin receptor family comprises multiple subtypes with distinct structural and functional characteristics. In the conventional classification, 5-HT receptors are grouped into the 5-HT1, 5-HT2, 5-HT3, 5-HT4, 5-HT5, 5-HT6, and 5-HT7 subfamilies. All are G protein-coupled receptors (GPCRs), except for the 5-HT3 receptor, which is a ligand-gated ion channel [1,2].
Different receptor subtypes influence cellular function through distinct signaling mechanisms. For example, 5-HT1 receptors typically couple to Gi/o proteins, inhibiting adenylyl cyclase activity and regulating intracellular cAMP levels. 5-HT2 receptors primarily couple to Gq/11 proteins and activate phospholipase C-related signaling. By contrast, 5-HT4, 5-HT6, and 5-HT7 receptors generally couple to Gs proteins, promoting adenylyl cyclase activity and increasing cAMP production [1,2].
Differences in tissue distribution, ligand recognition, and signal transduction enable serotonin to participate in a wide range of physiological processes. The research value of the 5-HT2A receptor lies not only in its own signaling functions, but also in its connections with other receptors, intracellular signaling networks, and complex neurophysiological processes.
Figure 1. Overview of serotonin receptor families and their major signaling pathways.[1,2]
2. Molecular Structure and Expression Distribution of the 5-HT2A Receptor
2.1 Seven-Transmembrane Architecture and Ligand Recognition
The 5-HT2A receptor belongs to Class A GPCRs and has the characteristic architecture of seven transmembrane α-helices. Its N-terminus is extracellular and its C-terminus intracellular. The extracellular and intracellular loops, together with the transmembrane helices, contribute to receptor conformational stability, ligand recognition, and coupling to signaling proteins [3,4].
The ligand-binding pocket is formed primarily by the transmembrane helices. Interactions between a ligand and key amino acid residues in the pocket can shift the receptor’s conformational equilibrium and thereby influence recruitment of G proteins or other intracellular regulatory proteins. Even when acting on the same receptor, different ligands may stabilize distinct conformations, resulting in differences in signal strength, duration, or pathway preference [3,4].
A structural study of the 5-HT2A receptor published in 2020 revealed structural features associated with receptor activation by psychedelic compounds, providing direct structural evidence for understanding the relationship between ligand binding and G-protein coupling [4]. These findings also indicate that the receptor is not simply an “on/off” switch, but a signaling platform that can dynamically transition among multiple conformational states.
From a drug-development perspective, understanding the spatial features of the ligand-binding pocket and the relationship between receptor conformational changes and signal transduction can support structure-guided ligand design, mechanistic pharmacology studies, and candidate-molecule screening.
Figure 2. Schematic representation of the seven-transmembrane architecture of the 5-HT2A receptor.[3,4]
2.2 Distribution in the Central Nervous System and Peripheral Tissues
The 5-HT2A receptor is expressed in multiple regions of the central nervous system, with particularly high abundance in the cerebral cortex. Studies of human brain tissue have shown that 5-HT2A receptor mRNA is distributed across multiple neocortical regions and is present in pyramidal neurons across different cortical layers, as well as in some interneurons[5]. Other receptor localization studies have also identified abundant receptor-binding sites in regions such as the forebrain, cerebral cortex, and hippocampus[1].
In the cerebral cortex, the 5-HT2A receptor regulates neuronal excitability, synaptic transmission, and neural network activity. These functions provide a biological basis for its involvement in cognition, perception, and behavioral regulation. However, its specific effects depend on neuronal cell type, local neural circuits, and interactions with other receptors and neurotransmitter systems; they cannot be simply classified as either excitatory or inhibitory[1, 3].
The 5-HT2A receptor has also been reported in various peripheral cells and tissues, including platelets, fibroblasts, lymphocytes, and muscle cells[1]. However, its expression levels and physiological functions vary across different tissues.
3. Major Signaling Pathways of the 5-HT2A Receptor
3.1 The Canonical Gq/11–PLCβ Pathway
The canonical signaling mechanism of the 5-HT2A receptor primarily involves Gq/11 proteins. Upon receptor activation, Gq/11 proteins are activated and subsequently regulate phospholipase Cβ (PLCβ). PLCβ hydrolyzes the membrane phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2), generating two important second messengers: inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG) [1,2].
IP3 can bind to IP3 receptors on the endoplasmic reticulum and promote the release of intracellular calcium. DAG, together with calcium signaling, participates in the regulation of downstream pathways involving protein kinase C (PKC). These processes can affect cellular excitability, protein phosphorylation, gene expression, and other cellular responses.
However, the canonical pathway cannot fully explain all pharmacological effects of the 5-HT2A receptor. Different ligands, cellular backgrounds, and experimental conditions may affect signal amplitude, kinetics, and downstream responses[6].
3.2 Functional Selectivity and β-Arrestin-Related Signaling
An important concept in GPCR research is functional selectivity, also known as biased agonism. Different ligands can stabilize distinct receptor conformations and preferentially activate particular downstream pathways, such as G-protein-mediated signaling or β-arrestin-related processes [6,7].
β-arrestin initially attracted attention for its roles in receptor desensitization and internalization. Following receptor activation, receptor phosphorylation and β-arrestin recruitment can affect receptor–G-protein interactions and contribute to receptor internalization, intracellular trafficking, and regulation of certain downstream signals. For the 5-HT2A receptor, the relative contributions of G-protein- and β-arrestin-related signaling may vary with ligand properties, receptor expression levels, and experimental systems [6,7].
Figure 3. Major signaling pathways associated with the 5-HT2A receptor.[2,6,7]
4. The 5-HT2A Receptor in Neuropsychiatric Disorders: From Biological Mechanisms to Potential Therapeutic Targets
The 5-HT2A receptor is widely involved in neurotransmitter regulation in the central nervous system. By influencing neuronal excitability, glutamatergic signaling, and neural-network activity, it contributes to physiological processes such as cognition, mood, perception, and behavior. These functions make it an important target in research on schizophrenia, depression, and other neuropsychiatric disorders [2,6]. However, involvement in disease-related pathways does not mean that the receptor has the same direction of effect across all disorders; its impact depends on disease context, cell type, signaling pathway, and mode of drug action [6,7].
4.1 Schizophrenia: The 5-HT2A Receptor and Glutamatergic Signaling
The 5-HT2A receptor has long been studied in the context of schizophrenia. Landmark research found that it can form a receptor complex with the metabotropic glutamate receptor mGlu₂ and may jointly regulate neural signals associated with psychotic symptoms. This finding offers an important clue to understanding interactions between serotonergic and glutamatergic systems [8].
In drug development, 5-HT2A receptor antagonism is an important component of the pharmacology of some atypical antipsychotics. However, these drugs usually act on other targets, including dopamine D₂ receptors, so their clinical efficacy cannot be attributed solely to the 5-HT2A pathway. Studying ligand recognition, signal modulation, and interactions with other receptors may further clarify the receptor’s potential role in schizophrenia [6,8].
4.2 Depression: Serotonergic Modulation and Emerging Treatment Strategies
The 5-HT2A receptor has also attracted interest in depression research. Serotonergic signaling is involved in mood and cognition, while some emerging drug candidates activate the 5-HT2A receptor to investigate potential modulation of neural-network activity and mood-related processes [2,6,9].
Research on psilocybin provides one example: its active metabolite can act on the 5-HT2A receptor, and studies are investigating its therapeutic potential in conditions such as treatment-resistant depression [9,10]. Receptor activation does not necessarily produce an antidepressant effect; outcomes are also influenced by pharmacological properties, dosing regimen, treatment setting, and patient characteristics. Clarifying how different ligands regulate receptor conformation and downstream signaling is therefore an important research direction [6,7].
4.3 Psychedelic Effects and Biased Signaling: From Receptor Activation to Functional Differences
The 5-HT2A receptor is one of the key pharmacological targets through which classical psychedelics produce subjective perceptual effects [9]. Different ligands may trigger distinct magnitudes or patterns of G-protein signaling, β-arrestin-related signaling, and other cellular responses. This phenomenon is known as biased signaling and is an important focus of current receptor pharmacology research [6,7].
Researchers seek to understand how ligand-induced conformational changes affect downstream signaling and whether these differences are associated with therapeutic effects or adverse reactions. However, measurements of signaling bias can be influenced by assay systems, cellular backgrounds, and analytical methods; more evidence is needed to establish their relationship with clinical outcomes [6,7].
Overall, the 5-HT2A receptor is not associated with only one disease or a single signaling pathway. Its potential roles across disorders depend on its structure and ligand-binding properties, as well as the cellular environment, downstream signaling, and interactions with other molecules [6–8].
5. Progress in Drug Development Targeting the 5-HT2A Receptor
Preliminary searches have identified more than 300 drug programs related to the 5-HT2A receptor. Because some programs have been discontinued, have made no progress for an extended period, or have unclear development statuses, this review focuses on 85 marketed drugs or candidates in clinical development (see the attached list). These drugs include 5-HT2A receptor antagonists, inverse agonists, agonists, and agents with activity at multiple receptors. Their indications are mainly concentrated in psychotic disorders such as schizophrenia, depression, bipolar disorder, and psychosis-related symptoms in Parkinson’s disease. In recent years, candidates based on 5-HT2A receptor agonism have also become a growing focus in depression research, further broadening the potential applications of this target.
- Selected Drugs and Development Updates
Milsaperidone (Bysanti) is an atypical antipsychotic whose pharmacology involves receptors including 5-HT2A and dopamine D₂. In 2026, it was approved in the United States for schizophrenia in adults and for acute manic or mixed episodes associated with bipolar I disorder, representing a recent development among 5-HT2A-related drugs.
Pimavanserin (Nuplazid) is a drug with 5-HT2A receptor inverse agonist activity, used primarily to treat psychotic symptoms associated with Parkinson’s disease, such as hallucinations and delusions. Unlike traditional antipsychotics, its approach focuses on improving symptoms by modulating serotonergic receptor pathways rather than relying primarily on dopamine D₂ receptor blockade.
Lumateperone (Caplyta) is an atypical antipsychotic that acts on multiple neurotransmitter systems, including 5-HT2A and dopamine D₂ receptors. In the United States, it has been approved for schizophrenia in adults and depressive episodes associated with bipolar disorder, and as an adjunctive treatment for major depressive disorder in adults. It illustrates the use of multi-receptor modulation in the treatment of psychiatric conditions.
Brexpiprazole (Rexulti) has a multi-receptor pharmacological profile, including 5-HT2A receptor antagonism and modulation of 5-HT₁A and dopamine D₂ receptors. It is approved for schizophrenia, adjunctive treatment of major depressive disorder in adults, and agitation associated with Alzheimer’s disease, illustrating the potential of multi-target drugs across psychiatric and neurological conditions.
COMP360 (synthetic psilocybin) is a candidate drug developed by Compass Pathways and is a 5-HT2A receptor agonist being investigated primarily for its potential to treat treatment-resistant depression. It has entered pivotal Phase III clinical studies, and in 2026 the company advanced a rolling submission and review process for a U.S. new drug application. It should nevertheless be classified as an investigational candidate rather than an approved marketed drug at the time described in the source.
CYB-003 is a deuterated psilocybin derivative developed by Helus Pharma (formerly Cybin). It is designed to exert potential antidepressant effects by modulating pathways that include the 5-HT2A receptor. The candidate is undergoing Phase III development for major depressive disorder, reflecting efforts to optimize molecular structures and explore the use of compounds related to classical psychedelics in psychiatric treatment.
Bretisilocin (GM-2505) is a candidate drug with 5-HT2A receptor agonist activity that can also promote serotonin release. It was initially developed by Gilgamesh Pharmaceuticals, which was later acquired by AbbVie. The drug is being developed primarily for moderate-to-severe major depressive disorder, and publicly available development information cited in the source places it in Phase II clinical development. It represents an exploration of novel serotonergic modulators for depression.
6. From Drug Development to Target Research: Tools for Studying the 5-HT2A Receptor
The 5-HT2A receptor has been explored in drug development for schizophrenia, depression, and other neuropsychiatric disorders. Drugs differ in how they act on this receptor, while receptor conformation, ligand-binding properties, and downstream signaling responses also affect how their mechanisms of action are understood and evaluated.
Obtaining 5-HT2A receptor protein that retains a native-like conformation is an important foundation for receptor-binding studies, ligand screening, and mechanistic research. For seven-transmembrane receptors, the membrane environment is critical to stability, conformation, and molecular interactions. DIMA’s proprietary Synthetic Nanodisc full-length membrane protein platform presents full-length membrane proteins in a lipid environment, retains the complete transmembrane structure, and is designed to better preserve a native-like conformation. It supports ligand-binding, structural, and functional studies of membrane proteins such as GPCRs. DIMA currently offers full-length 5-HT2A protein in Synthetic Nanodisc format.
Human 5HT2A-Strep full length protein-synthetic nanodisc
（Cat.No.FLP120166）
Left: SDS-PAGE analysis of Human 5HT2A-Strep-Nanodisc. Right: ELISA binding analysis of Human 5HT2A-Strep-Nanodisc to an anti-Flag monoclonal antibody (EC50= 4.320 ng/mL).
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References
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- Pourhamzeh M, Ghasemi Moravej F, Arabi M, et al. The Roles of Serotonin in Neuropsychiatric Disorders. Cellular and Molecular Neurobiology. 2022;42(6):1671–1692.
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- Burnet PWJ, Eastwood SL, Lacey K, Harrison PJ. The distribution of 5-HT1A and 5-HT2A receptor mRNA in human brain. Brain Research. 1995;676(1):157–168.
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- Jastrzębski MK, Wójcik P, Grudzińska A, et al. Biased signaling via serotonin 5-HT2A receptor: From structural aspects to in vitro and in vivo pharmacology. Acta Pharmaceutica Sinica B. 2025;15(9):4438–4455.
- González-Maeso J, Ang RL, Yuen T, et al. Identification of a serotonin/glutamate receptor complex implicated in psychosis. Nature. 2008;452:93–97.
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- Goodwin GM, Aaronson ST, Alvarez O, et al. Single-Dose Psilocybin for a Treatment-Resistant Episode of Major Depression. New England Journal of Medicine. 2022;387(18):1637–1648.
Appendix: Marketed Drugs and Clinical-Stage Drug Candidates Related to the 5-HT2A Receptor
