Motivation and emotion/Book/2025/GLP-1 receptor agonists and hunger

GLP-1 receptor agonists and hunger:
How do GLP-1 receptor agonists such as semaglutide affect subjective feelings of hunger and appetite regulation?

Overview

Scenario

Ari, 28, struggles with weight loss despite repeated efforts to reduce her body weight. She often finds the most challenging part after starting a diet are the strong feelings of hunger (see Figure 1), making weight loss difficult to maintain [missing something?] starts a weekly GLP-1 medicine after discussing options with her clinician. Within a few weeks, she notices earlier fullness at meals and less urge to snack late at night. Mild nausea settles with a slower dose increase and smaller, lower-fat meals. Over time, her pre-meal hunger feels quieter and she’s more comfortable leaving food on the plate. These changes in how hungry she feels make it easier to keep portions smaller and reduce snacking.

Everyday eating is guided by how hungry we feel, how quickly we become full, and how much we want food. GLP-1 receptor agonists (GLP-1RAs) are notable because people often report feeling less hungry with earlier fullness alongside clinically meaningful weight loss (Drucker et al., 2017; Moiz et al., 2025). This chapter explains how GLP-1RAs change the experience of appetite: what happens in the gut, what signals travel via the vagus nerve to the brain, how central circuits adjust motivation to eat, and what human studies show about subjective appetite ratings and food intake (Chen et al., 2021; Trapp & Brierley, 2021).

Focus questions:

Where does GLP-1 act in the body and brain to influence hunger?
How do vagal and central GLP-1 mechanisms differ and how do they interact?
What do human studies show about subjective appetite (hunger, fullness, desire to eat) on GLP-1RAs[improve clarity]?

Background

This section gives the essential context for the rest of the chapter. It clarifies what GLP-1 is and where it is made, traces the path from incretin biology to approved therapies, and outlines the main GLP-1 receptor agonists with a brief note on tirzepatide. It also explains why appetite regulation matters for health and motivation.

What is GLP-1?

Glucagon-like peptide-1 (GLP-1) is a peptide hormone encoded by proglucagon. It is released after meals by intestinal L-cells and is also synthesised by a distinct group of preproglucagon neurons in the nucleus tractus solitarius of the brainstem. GLP-1 acts peripherally and centrally to integrate metabolic state with motivated eating and related behaviours (Chen et al., 2021; Drucker et al., 2017; Trapp & Brierley, 2021;). Native GLP-1 is rapidly inactivated by dipeptidyl peptidase-4, which gives it a short plasma half-life. This property is a key reason long-acting GLP-1 receptor agonists were developed to provide sustained receptor engagement (Drucker et al., 2017).

GLP-1 RAs as a clinical tool

Following characterisation of the incretin effect, GLP-1 was shown to enhance glucose-dependent insulin secretion, suppress inappropriate glucagon in hyperglycaemia, slow gastric emptying, and interact with vagal pathways. Identification of dipeptidyl peptidase-4 as the main inactivating enzyme prompted strategies that prolong exposure, including peptide modification that increases albumin binding and reduces renal clearance. These advances enabled weekly semaglutide dosing with robust clinical effects (Drucker et al., 2017; Friedman, 2024). Early GLP-1 receptor agonists produced modest weight loss relative to control across people with and without type 2 diabetes in randomised trials and meta-analysis (Vilsbøll et al., 2012). Higher-dose programs for obesity later demonstrated larger and more durable effects, with participants commonly reporting reduced hunger and earlier fullness in parallel with weight loss (Friedman, 2024).

GLP-1RA types

There are a variety of GLP-1RAs types that having varying effects on hunger. This chapter focuses on semaglutide but a table of different GLP-1RAs is also included (see Table 1).

Table 1. Table of GLP-1RAs
Drug	Class	Dosing
Semaglutide	GLP-1RA	Weekly, subcutaneous
Liraglutide	GLP-1RA	Daily, subcutaneous
Exenatide	GLP-1RA	Twice daily, subcutaneous
Dulaglutide	GLP-1RA	Weekly, subcutaneous
Tirzepatide	Dual GIP/GLP-1 agonist	Weekly, subcutaneous

(Latif et al., 2025; Nauck et al., 2021; Vilsbøll et al., 2012)

Dangers of obesity

Obesity is a worldwide (see Figure 3) chronic, relapsing condition that elevates cardiometabolic risk and shortens healthspan. Excess adiposity raises blood pressure, worsens lipid profiles, accelerates atherosclerotic cardiovascular disease, increases osteoarthritis burden, and raises risks for non-alcoholic fatty liver disease, certain cancers, and sleep apnoea (Dixon, 2010). Pharmacotherapies that reduce energy intake and support weight loss therefore serve not just weight management but broader risk management (Friedman, 2024). Early GLP-1A meta-analyses reported consistent weight reduction, modest with first-generation agents and larger with later molecules,supporting pharmacological appetite modulation as a viable strategy (Vilsbøll et al., 2012). Contemporary clinical programs confirm greater effect sizes, especially at obesity-indicated doses (Moiz et al., 2025), with real-world cohorts demonstrating effectiveness outside of trial settings (Ghusn et al., 2022).

How do GLP-1 RAs work?

This section describes how GLP-1 receptor agonists influence appetite from body to brain. It starts with effects on gastric emptying and the feeling of fullness during a meal, then follows signals along the vagus nerve to the nucleus tractus solitarius and area postrema, and finishes with central circuits in the hypothalamus and mesolimbic system. Together these routes explain both earlier satiation at meals and a quieter background drive to eat.

Gastric emptying

GLP-1 receptor agonists slow gastric emptying, particularly early in treatment. Slower delivery of nutrients from the stomach to the small intestine increases feelings of fullness during a meal and reduces meal size[factual?]. This change aligns with the early pattern many people report, which is a quicker rise in fullness and a lower desire to continue eating[factual?]. In pharmacology studies, the gastric emptying effect is strongest in the first weeks and may attenuate over time, while reductions in hunger and energy intake can persist through other pathways that act within the brain (Drucker et al., 2017; Moiz et al., 2025). In a 20-week trial of semaglutide 2.4 mg, participants showed lower hunger ratings and reduced ad libitum intake. This pattern illustrates how slowed gastric transit and perceived satiation co-occur early in therapy (Friedrichsen et al., 2021).

Vagus and NTS

Peripheral GLP-1 signals interact with vagal nerves that carry interoceptive information from the gut to the brainstem. Cell bodies in the nodose ganglion project to the nucleus tractus solitarius and the nearby area postrema, which is a circumventricular organ (CVO) that detects circulating signals. Activation of these pathways informs the brain that a meal is underway and eating should be stopped soon. The result is an earlier sense of satiation that complements the effect of slower gastric emptying. These hindbrain sites are positioned to integrate gut signals with behavioural control of eating and provide a gateway through which exogenous GLP-1 receptor agonists can influence appetite (Drucker et al., 2017; Trapp & Brierley, 2021).

Central circuits

A second route begins inside the brain. Preproglucagon neurons in the nucleus tractus solitarius produce GLP-1 that projects to hypothalamic and mesolimbic targets. In the hypothalamus, GLP-1 receptor activation causes feelings of satiety. In mesolimbic regions such as the ventral tegmental area and nucleus accumbens, GLP-1 signalling reduces the motivational pull of food cues (Secher et al., 2014). Experimental work shows that hypothalamic arcuate-nucleus circuitry is required for GLP-1 receptor agonist–induced energy-intake suppression and weight loss, which supports a central contribution to sustained appetite change (Secher et al., 2014). These central effects shift the expected value of eating, which lowers the desire to initiate a meal and reduces cue-driven snacking. Further, studies show GLP-1 receptor activation lowers excitability in several appetite-relevant nuclei, which provides a mechanistic basis for the sustained lowering of hunger reports in longer studies, even when gastric emptying effects have partly diminished (Chen et al., 202; Trapp & Brierley, 2021).

The vagal and central systems are partly independent and also interactive (See Figure 4). Peripheral signals that arrive at the hindbrain can influence central preproglucagon output. Central signals can, in turn, modulate the motivation of food. Together they explain why people often report both quicker fullness during meals and a quieter background drive to eat across the day. The dual-route view is consistent with clinical observations that appetite reduction is detectable early and then remains evident with continued treatment and stable dosing (Drucker et al., 2017; Trapp & Brierley, 2021).

Case study

If Ari shows stable or improving hunger ratings at week 12 while gastric emptying proxies have moved toward baseline, a central mechanism likely explains the continuing subjective appetite benefit. If instead she mainly shows larger within-meal fullness and smaller immediate meal size early on, a vagal mechanism likely accounts for the effect profile.

Quiz

Exogenous and Endogenous GLP-1RAs

GLP-1 is produced in both the GI tract, along with the brain. These differences mean that GLP-1 acts as both a hormone within the periphery system, and a neurotransmitter within the CNS. Further, GLP-1A drugs affect both of these systems, combining many of the effects seen in each area.

Endogenous Sources

The body produces GLP-1 in two distinct and mostly separate systems. In the GI tract post-prandial L- cell secretion releases GLP-1 into the portal circulation, modulating islets, liver, gastrointestinal motility, and vagal terminals; this pool of GLP-1 is largely peripheral and subject to rapid DPP-4 degradation (Drucker et al., 2017). In parallel, preproglucagon neurons synthesize GLP-1 within the CNS, projecting to hypothalamic and mesolimbic targets that regulate homeostatic and hedonic feeding (Trapp & Brierley, 2021).

Exogenous Sources

Pharmacological GLP-1As bind GLP-1 receptors throughout the body and can access hindbrain regions with relatively porous blood brain barrier (BBB) (e.g., area postrema) and engage vagal terminals, while also influencing hypothalamic and mesolimbic circuits that shape eating motivation (Trapp & Brierley, 2021). Studies shows GLP-1R activation produces depolarization and modulates glutamatergic/GABAergic transmission in relevant nuclei, consistent with satiety signalling and reduced drive to eat (Chen et al., 2021). Clinically, these mechanisms converge to reduce hunger and snacking, increase meal fullness, and lower ad libitum intake (Moiz et al., 2025).

How they interact

It is important to emphasise that peripheral L-cell GLP-1 and central preproglucagon GLP-1 are distinct systems, yet they interact at integrative nodes such as the NTS and area postrema (Trapp & Brierley, 2021). Exogenous GLP-1As act on both of these systems and help explain why the drugs influence the feeling of hunger through both early satiation (gut, vagus, hindbrain) and altered motivation (central networks).

Quiz

Subjective appetite

Subjective appetite refers to self-reported feelings of hunger, fullness, satiety, and desire to eat that are measured with validated scales during standardised meals or in daily life. This section explains how these feelings change after starting GLP-1 receptor agonists, what is typically seen in the first weeks compared with later maintenance, and how ratings relate to behaviour at ad libitum meals.

Acute to short-term effects

Across early treatment studies, GLP-1 receptor agonists lower self-reported hunger, increase fullness and satiety, and reduce energy intake during ad libitum meals. These effects are detectable within days to weeks, often before large weight changes occur, which suggests a primary action on appetite and meal-by-meal regulation rather than a secondary consequence of weight loss (Friedrichsen et al., 2021; Vilsbøll et al., 2012). In a 20-week semaglutide trial that included standardised test meals, participants reported lower hunger and higher fullness together with reduced ad libitum intake, while a paracetamol absorption test supported a slowing of gastric emptying early in treatment (Friedrichsen et al., 2021). These findings align with a physiological account in which delayed gastric delivery, vagal afferent input to the hindbrain, and early meal termination contribute to the felt experience of quicker satiation during meals (Drucker, Habener, & Holst, 2017).

Long-term effects and real-world observations

With continued dosing and stabilisation of side effects, participants commonly describe a quieter background drive to eat, fewer cue-triggered urges, and easier portion control across the day[factual?]. Studies that track subjective appetite across months of treatment report sustained reductions in hunger and improved control of eating, even as gastric emptying effects may attenuate relative to the first weeks[factual?]. This pattern is consistent with a greater contribution from central circuits that lower incentive salience of food and support day-to-day control of eating (Friedrichsen et al., 2021; Trapp & Brierley, 2021). Real-world large, randomised trials indicated semaglutide show clinically meaningful weight loss, producing sustained improvements in control of eating and clinically meaningful weight loss over 68 weeks (Wilding et al., 2021). The effectiveness signal [grammar?] in practice supports external validity for appetite-linked mechanisms observed in trials, although routine care rarely includes standardised appetite scales (Ghusn et al., 2022).

With vs without T2D

Trials and meta-analyses indicate that people with and without type 2 diabetes experience reductions in hunger and energy intake on GLP-1 receptor agonists, although absolute weight loss is often larger in obesity-dose programs that recruit primarily non-diabetic participants[factual?]. The appetite signal is directionally similar in both groups and appears linked to dose, exposure time, and adherence rather than diabetes status per se (Drucker et al., 2017; Moiz et al., 2025; Vilsbøll et al., 2012). Glycaemic benefits in diabetes cohorts are important clinically, but they do not fully account for the subjective appetite changes, which reflect gut-brain signalling and central modulation of eating motivation in both populations (Drucker et al., 2017).

Psychological interpretation

From a motivational perspective, GLP-1As likely lower the expected utility of eating by reducing interoceptive hunger and cue-driven wanting through mesolimbic modulation, shifting cost-benefit appraisals away from immediate consumption and enabling adherence to smaller portions (Trapp & Brierley, 2021).

Quiz

Side effects

The most common adverse effects are nausea, vomiting, abdominal discomfort, and sometimes constipation[factual?]. Early nausea can confound appetite ratings as a participant may endorse “less hunger” because interoceptive aversion reduces desire to eat[factual?]. Clinical practice minimizes this by gradual titration (Moiz et al., 2025; Vilsbøll et al., 2012). Over time, as GI tolerance improves, reduced hunger and earlier satiation more clearly reflect satiety signalling rather than aversion (Moiz et al., 2025). Serious risks (e.g., gallbladder events, rare pancreatitis) are uncommon but have been noted (Friedman, 2024; Moiz et al., 2025).

Conclusion

This chapter explains how GLP-1 receptor agonists such as semaglutide change the felt experience of appetite. It shows where GLP-1 signals act in the body and brain, how the vagal and central routes differ yet work together, and what human studies report about hunger, fullness, and eating behaviour. Early after starting treatment, slower gastric emptying and stronger gut to brain signalling produce quicker fullness within meals and smaller ad libitum intake. With continued dosing, central circuits in the hypothalamus and mesolimbic system become more prominent and people describe a quieter background drive to eat and fewer cue driven urges. These patterns appear in adults with and without type 2 diabetes and often emerge before large weight change. Across trials that use standardised meals and visual analogue scales, the consistent picture is lower hunger, higher fullness, and better control of eating.

The take-home message is that GLP-1 therapy aligns physiology with goals by recalibrating hunger and satiety signals. Vagal influences shape the meal you are eating, while central influences shape what, when, and how much you want to eat across the day. Appetite ratings should be interpreted with care in the first weeks when gastrointestinal symptoms can blur perception, then read alongside intake as tolerance improves. Understanding these routes allows people to make informed decisions about their body and semaglutide use.

References

Chen, X.-Y., Chen, L., Yang, W., & Xie, A.-M. (2021). GLP-1 suppresses feeding behaviours and modulates neuronal electrophysiology in multiple brain regions. Frontiers in Molecular Neuroscience, 14, 793004. https://doi.org/10.3389/fnmol.2021.793004

Dixon, J. B. (2010). The effect of obesity on health outcomes. Endocrine Aspects of Obesity, 316(2), 104–108. https://doi.org/10.1016/j.mce.2009.07.008

Drucker, D. J., Habener, J. F., & Holst, J. J. (2017). Discovery, characterization, and clinical development of the glucagon-like peptides. The Journal of Clinical Investigation, 127(12), 4217–4231*. https://doi.org/10.1172/JCI97233

Friedman, J. M. (2024). The discovery and development of GLP-1–based drugs that have revolutionized the treatment of obesity. Proceedings of the National Academy of Sciences, 121(39), e2415550121*. https://doi.org/10.1073/pnas.2415550121

Friedrichsen, M., Breitschaft, A., Tadayon, S., Wizert, A., & Skovgaard, D. (2021). The effect of semaglutide 2.4 mg once weekly on energy intake, appetite, control of eating, and gastric emptying in adults with obesity. Diabetes, obesity & metabolism, 23(3), 754–762. https://doi.org/10.1111/dom.14280

Ghusn, W., De la Rosa, A., Sacoto, D., Cifuentes, L., Campos, A., Feris, F., Hurtado, M. D., & Acosta, A. (2022). Weight loss outcomes associated with semaglutide treatment for patients with overweight or obesity. JAMA Network Open, 5(9), e2231982*. https://doi:10.1001/jamanetworkopen.2022.31982 Holst, J.J. (2022).

Jastreboff, A. M., Aronne, L. J., Ahmad, N. N., Wharton, S., Connery, L., Alves, B., Kiyosue, A., Zhang, S., Liu, B., Bunck, M. C., Stefanski, A., & SURMOUNT-1 Investigators. (2022). Tirzepatide once weekly for the treatment of obesity. New England Journal of Medicine, 387(3), 205–216. https://doi.org/10.1056/NEJMoa2206038

Latif, W., Lambrinos, K. J., Patel, P., & Rodriguez, R. (2024, February 25). Compare and contrast the glucagon-like peptide-1 receptor agonists (GLP1RAs). In StatPearls. StatPearls Publishing. Retrieved September 30, 2025, from https://www.ncbi.nlm.nih.gov/books/NBK572151/

Discovery of the GI Effects of GLP-1: An Historical Perspective. Dig Dis Sci 67, 2716–2720. https://doi.org/10.1007/s10620-022-07519-3

Moiz, A., Filion, K. B., Tsoukas, M. A., Yu, O. H. Y., Peters, T. M., & Eisenberg, M. J. (2025). GLP-1 receptor agonist–induced weight loss: Central and peripheral mechanisms and clinical implications. The American Journal of Medicine, 138(6), 935–945*. https://doi.org/10.1016/j.amjmed.2025.01.021

Nauck, M. A., & D'Alessio, D. A. (2022). Tirzepatide, a dual GIP/GLP-1 receptor co-agonist for the treatment of type 2 diabetes with unmatched effectiveness regrading glycaemic control and body weight reduction. Cardiovascular diabetology, 21(1), 169. https://doi.org/10.1186/s12933-022-01604-7

Secher, A., Jelsing, J., Baquero, A. F., Hecksher-Sørensen, J., Cowley, M. A., Dalbøge, L. S., Hansen, G., Grove, K. L., Pyke, C., Raun, K., Schäffer, L., Tang-Christensen, M., Verma, S., Witgen, B. M., Vrang, N., & Bjerre Knudsen, L. (2014). The arcuate nucleus mediates GLP-1 receptor agonist liraglutide-induced weight loss. Journal of Clinical Investigation, 124(10), 4473–4488. https://doi.org/10.1172/JCI75276

Trapp, S., & Brierley, D. I. (2021). Brain GLP-1 and the regulation of food intake: GLP-1 action in the brain and its implications for GLP-1 receptor agonists in obesity treatment. British Pharmacological Society, 179(4), 557–570*. https:// doi: 10.1111/bph.15638

Vilsbøll, T., Christensen, M., Junker, A. E., Knop, F. K., & Gluud, L. L. (2012). Effects of glucagon-like peptide-1 receptor agonists on weight loss: Systematic review and meta-analyses of randomised controlled trials. BMJ, 344, d7771. https://doi:10.1136/bmj.d7771

Wilding, J. P. H., Batterham, R. L., Calanna, S., Davies, M., Van Gaal, L. F., Lingvay, I., McGowan, B. M., Rosenstock, J., Tran, M. T., Wadden, T. A., Wharton, S., Yokote, K., Zeuthen, N., Kushner, R. F., & STEP 1 Study Group. (2021). Once-weekly semaglutide in adults with overweight or obesity. New England Journal of Medicine, 384(11), 989–1002. https://doi.org/10.1056/NEJMoa2032183

External links

The brain science of obesity(Tedx Talk)

The Science of Hunger & Medications to Combat Obesity | Dr. Zachary Knight and Andrew Huberman (Huberman Podcast)

	Decreased ghrelin release
	Slowed gastric emptying and vagal signalling to NTS
	Enhanced hepatic gluconeogenesis
	Peripheral insulin resistance

	They are the same system; peripheral GLP-1 simply crosses the BBB to become central GLP-1.
	They are distinct but interacting systems that can each suppress feeding.
	The central system only influences thirst.
	The peripheral system only affects pancreatic insulin and not appetite.

	Because participants consciously restrict food regardless of hunger.
	Because GLP-1As permanently damage taste receptors.
	Because central GLP-1-responsive circuits continue to modulate satiety and reward.
	Because GLP-1As increase basal metabolic rate dramatically.