# Xylazine Interaction with Opioid Receptors: Binding and Signaling

> **NIH DA R21** · UNIVERSITY OF ROCHESTER · 2026 · $192,500

## Abstract

Project Summary/Abstract
This resubmitted R21 proposal is in response to the Notice of Special Interest (NOSI): Xylazine:
Understanding Its Use and Consequences, NOT-DA-24-012. The goal of this study is to determine if
xylazine and its metabolites act as agonists or positive allosteric modulators (PAMs) at the mu and
kappa opioid receptors (MOR, KOR). Additional studies will determine if xylazine and its metabolites
are agonists, antagonists, or inverse agonists at the sigma 1 (s1R) and sigma 2 receptors (s2R).
Xylazine binds with nM affinity to the sigma receptors. Illegal drugs, particularly fentanyl and stimulants, are
being mixed with xylazine to enhance drugs effects or increase street value by increasing weight. Xylazine
is not approved for human use. Xylazine is historically regarded as an α2-adrenergic receptor agonist based
on physiological studies using α2-adrenergic receptor antagonists. However, a recent studies showed that
the opioid antagonist naloxone induced withdrawal from xylazine in mice and xylazine had micromolar affinity
for the α2-adrenergic receptor. Our preliminary data shows that xylazine had a Ki value of 330 ± 13 nM
for inhibiting binding to the human KOR. Xylazine also inhibited forskolin-induced cyclic AMP levels
in CHO cells expressing the human KOR and stimulated G protein activity as measured by a BRET
assay. The following Specific Aims will characterize the potency and pharmacological properties of xylazine.
Aim 1 will determine if xylazine and its metabolites act as PAMs at the MOR and KOR as shown with G protein
and β-arrestin signaling. Bias signaling through the six Gαi/o/z proteins will be determined and compared with
results obtained with β-arrestin recruitment. In addition, experiments will determine if xylazine and its metabolites
inhibit forskolin-stimulated cAMP as an agonist or as a PAM. Radioligand binding experiments will determine if
xylazine acts as a PAM by increasing the affinity of agonists such as fentanyl for the

## Key facts

- **NIH application ID:** 11323119
- **Project number:** 5R21DA061044-02
- **Recipient organization:** UNIVERSITY OF ROCHESTER
- **Principal Investigator:** JEAN M BIDLACK
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** DA
- **Fiscal year:** 2026
- **Award amount:** $192,500
- **Award type:** 5
- **Project period:** 2025-05-01T00:00:00 → 2027-04-30T00:00:00

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/11323119

## Citation

> US National Institutes of Health, RePORTER application 11323119, Xylazine Interaction with Opioid Receptors: Binding and Signaling (5R21DA061044-02). Retrieved via AI Analytics 2026-07-12 from https://api.ai-analytics.org/grant/nih/11323119. Licensed CC0.

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