New Study Clarifies Multimodal Mechanism of Viloxazine in ADHD

Viloxazine is a non-stimulant medication indicated for the treatment of attention-deficit/hyperactivity disorder (ADHD) in children and adults.^1,2 In contrast to stimulants, which directly affect dopamine release and reuptake,³ non-stimulants indirectly affect dopamine signaling by selectively blocking the norepinephrine transporter (NET).^2,3 Viloxazine’s potency against NET is lower compared with other non-stimulants, which suggests its efficacy may result from pharmacodynamic factors beyond NET inhibition.⁴ A recent study sought to validate and expand on the molecular mechanism of viloxazine by evaluating its effects on NET as well as individual serotonin (5-HT) receptors.⁵  

Key Results 

Using in vitro binding competition assays, the study showed that viloxazine had moderate affinity for NET (K_i = 0.13 µM) and very weak affinity for the serotonin transporter (SERT) (K_i = 14.00 µM). Furthermore, viloxazine had moderate affinity for 5-HT receptors, with a summary affinity ranking of transporters and receptors assayed as NET > 5-HT_2C ≈ 5-HT_2B > 5-HT₇ >> 5-HT_2A >>> SERT.⁵  

In vitro functional assays demonstrated that viloxazine acts as a NET inhibitor (IC₅₀ = 0.370 µM), a partial agonist at 5-HT_2C receptors (EC₅₀ = 1.6 µM), and a weak antagonist at 5-HT_2B (IC₅₀ = 36.4 µM) and 5-HT₇ receptors (IC₅₀ = 27.2 µM). Importantly, predicted receptor occupancy modeling suggested that clinically relevant unbound plasma concentrations of viloxazine could produce >80% occupancy of NET, 40% to 85% occupancy of 5-HT_2C and 5-HT_2B receptors, and 20% to 66% occupancy of 5-HT₇ receptors. Ex vivo studies in rat brains further confirmed substantial NET occupancy (67% to 94%) across therapeutically relevant concentrations of viloxazine.⁵  

Study Limitations 

It’s important to consider that the in vitro and ex vivo assays used in this study do not exactly replicate viloxazine effects on NET and 5-HT receptors in the human brain. Therefore, future in vivo investigations, such as PET studies in humans, could further enhance the understanding of viloxazine mechanisms.⁵ 

Clinical Implications 

These findings challenge the conventional characterization of viloxazine as solely a norepinephrine reuptake inhibitor. Although NET inhibition appears central to its pharmacology, the demonstrated 5-HT receptor activity suggests a broader, multimodal mechanism involving direct effects on 5-HT_2C, 5-HT_2B, and 5-HT₇ receptors.⁵ The therapeutic relevance of viloxazine’s effects on 5-HT receptors is not yet fully understood; however, it is possible that partial agonism of 5-HT_2C could help reduce impulsivity, and antagonism of 5-HT₇ and 5-HT_2B has been implicated in the treatment of depression.^6-8 Overall, the study advances the understanding of viloxazine’s mechanism of action and suggests that serotonergic receptor engagement may represent an underrecognized therapeutic pathway in ADHD treatment. 

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References

1. Qelbree (viloxazine extended-release capsules). Prescribing information. Supernus Pharmaceuticals, Inc; 2025. Accessed May 21, 2026. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/211964s013lbl.pdf.  
2. Haddad HW, Hankey PB, Ko J, et al. Viloxazine, a non-stimulant norepinephrine reuptake inhibitor, for the treatment of attention deficit hyperactivity disorder: a 3 year update. Health Psychol Res. 2022;10(3):37018. doi:10.52965/001c.37018 
3. Brown KA, Samuel S, Patel DR. Pharmacologic management of attention deficit hyperactivity disorder in children and adolescents: a review for practitioners. Transl Pediatr. 2018;7(1):36-47. doi:10.21037/tp.2017.08.02 
4. Yu C, Garcia-Olivares J, Candler S, Schwabe S, Maletic V. New insights into the mechanism of action of viloxazine: serotonin and norepinephrine modulating properties. J Exp Pharmacol. 2020;12:285-300. doi:10.2147/JEP.S256586 
5. Garcia-Olivares J, Yegla B, Koch J, Yu C, Rubin J. Updated viloxazine pharmacology: experiments establish norepinephrine transporter occupancy and serotonin 5-HT_2C, 5-HT_2B, and 5-HT₇ receptor binding at therapeutically relevant concentrations. Drugs R D. 2026;26(1):129-139. doi:10.1007/s40268-026-00543-y 
6. Wold EA, Wild CT, Cunningham KA, Zhou J. Targeting the 5-HT2C receptor in biological context and the current state of 5-HT2C receptor ligand development. Curr Top Med Chem. 2019;19(16):1381-1398. doi:10.2174/1568026619666190709101449 
7. Gottlieb N, Li TY, Young AH, Stokes PR. The 5-HT7 receptor system as a treatment target for mood and anxiety disorders: A systematic review. J Psychopharmacol. 2023;37(12):1167-1181. doi:10.1177/02698811231211228 
8. Hamati R, El Mansari M, Blier P. Serotonin-2B receptor antagonism increases the activity of dopamine and glutamate neurons in the presence of selective serotonin reuptake inhibition. Neuropsychopharmacology. 2020;45(12):2098-2105. doi:10.1038/s41386-020-0723-y