SR-17018, the biased opioid that reframed the side-effect debate.

SR-17018 is a small molecule that activates the μ-opioid receptor (MOR), the same receptor engaged by morphine, fentanyl, and endogenous β-endorphin. What sets it apart is a pronounced signaling bias: at the receptor, SR-17018 recruits the intracellular protein β-arrestin2 far less efficiently than it triggers G-protein-coupled signaling.^[1]

The practical question that motivated its synthesis is simple but consequential. β-Arrestin2 recruitment at MOR has been linked in animal studies to the side effects that make opioids dangerous — respiratory depression, gastrointestinal slowdown, and tolerance — while the G-protein arm mediates analgesia. If a ligand could cleanly separate the two, the result might be a pain medicine with a wider therapeutic window. SR-17018 was designed as a tool compound for asking that question with a chemical probe.

In commerce, SR-17018 is supplied as third-party verified, high-purity (99%+) precision powder for use in in-vitro pharmacology, receptor binding assays, and preclinical rodent studies. It is not a clinical drug, is not approved for human use in any jurisdiction we are aware of, and is not sold or intended for human or veterinary consumption.

SR-17018 emerged from a medicinal-chemistry program at the Florida campus of Scripps Research, directed by Laura Bohn, PhD, whose laboratory has spent decades studying the downstream consequences of MOR signaling. The Bohn lab had previously shown, using β-arrestin2 knockout mice, that animals lacking β-arrestin2 retain morphine analgesia but show reduced respiratory depression and constipation. That genetic result raised an obvious pharmacological question: could the same biology be replicated with a small molecule that simply does not recruit β-arrestin2 in the first place?

SR-17018 was one of a family of compounds synthesized and characterized in that effort. It was reported alongside the broader bias factor framework in a 2017 paper in Cell titled “Bias Factor and Therapeutic Window Correlate to Predict Safer Opioid Analgesics.”^[1]The authors argued that bias factor — a quantitative measure of how selectively a ligand favors one receptor-signaling pathway over another — tracks the gap between an opioid's analgesic and respiratory-depressant doses in rodents. SR-17018 sat at the high-bias end of their series and correspondingly showed the widest therapeutic window in the reported assays.

This placed SR-17018 alongside two other much-discussed biased MOR agonists from roughly the same era: TRV130 (oliceridine), from Trevena, reported by DeWire and colleagues in 2013,^[4] and PZM21, reported by the Manglik group in a 2016 Nature paper.^[5] Of the three, oliceridine is the only one to have entered the clinic: it was approved in 2020 under the trade name Olinvyk for use in controlled hospital settings. TRV130 and PZM21 have since been the subject of considerable follow-up debate — see Current research status below.

A full pharmacology treatment lives in the companion page on the mechanism of action; the brief version follows.

SR-17018 binds the μ-opioid receptor and initiates G-protein-coupled signaling — activation of Gαᵢ subunits, inhibition of adenylyl cyclase, and reduction of intracellular cAMP — with potency in the high-nanomolar range in cell-based assays. Its defining property is that it does not efficiently drive β-arrestin2 recruitment at the receptor. When bias factor is computed using standard operational-model methodology, SR-17018 sits substantially higher than morphine, DAMGO, or TRV130.^[1]

In rodent models reported in the original paper, SR-17018 was analgesic in hot-plate and tail-flick assays at doses that were markedly below those that produced respiratory depression, providing a larger therapeutic index than morphine or oxycodone.^[1] Subsequent work from the Bohn lab has reported that chronic dosing does not produce the tolerance typically seen with morphine — a claim discussed in the next section.^[2]

The headline claim of the 2017 paper — that bias factor predicts a safer opioid — has been examined closely in the years since, and the field's consensus has shifted in important ways that anyone handling SR-17018 should understand before citing older summaries.

Follow-up work from the Bohn laboratory in 2020 reported that SR-17018 not only retained analgesic efficacy on chronic dosing in mice but actually reversed morphine tolerance when substituted after prolonged morphine administration, and did so without precipitating withdrawal.^[2] If these results hold up in other laboratories, SR-17018 is a more interesting pharmacological probe than the original paper suggested.

At roughly the same time, however, a separate group led by Meritxell Canals and Macdonald Christie, working with several biased agonists including TRV130 and PZM21, proposed an alternative interpretation of the underlying biology. In Science Signaling (2020), Gillis and colleagues argued that the apparent in-vivo advantage of some biased agonists can be explained not by signaling bias per se but by low intrinsic efficacy at MOR — the same pharmacological property that distinguishes morphine from fentanyl.^[3] Under this reading, biased agonism is a side effect of low efficacy rather than a separate mechanism, and the therapeutic-window benefits attributed to bias may be achievable with any sufficiently low-efficacy agonist.

A parallel thread of skepticism concerns PZM21 specifically. A 2018 paper in British Journal of Pharmacology reported that PZM21 does cause respiratory depression and does produce tolerance under conditions that differ modestly from the original characterization, undermining the idea that the observed benefits were uniquely attributable to signaling bias.^[6]

The net effect for SR-17018 is that it remains the most interesting published example of a highly biased MOR agonist with a credible in-vivo analgesic profile, but the mechanistic story is under active revision. Researchers working with the compound today should read the original 2017 paper, the 2020 Grim follow-up, and the 2020 Gillis Science Signaling paper together, not in isolation.

In active laboratory use, SR-17018 functions primarily as a tool compound — a chemical probe used to test hypotheses about opioid pharmacology rather than as a candidate therapy. Typical applications include:

• Signaling-pathway dissection. Paired with balanced agonists (DAMGO, morphine) and other biased agonists (TRV130, PZM21), SR-17018 helps isolate the downstream consequences of G-protein versus β-arrestin2 engagement at MOR.
• Therapeutic-window characterization. Rodent hot-plate, tail-flick, and plethysmography assays use SR-17018 as a reference compound when benchmarking new candidates.
• Tolerance and dependence models. The Grim 2020 findings motivated a wave of comparative studies on chronic-dosing regimens, rotation schedules, and morphine substitution.
• Receptor-kinetic and bias-factor studies. As operational-model methodology has been refined, SR-17018 has become a standard calibration point for bias calculations across competing analytical frameworks.
• Structural biology and receptor docking. Cryo-EM and computational studies of MOR use SR-17018's binding mode to probe how ligand features map to downstream signaling.

SR-17018 is not appropriate for pharmacokinetic studies in humans, any form of human clinical research, or any use in animals outside of approved research protocols reviewed by the appropriate institutional committees.

SR17 Labs supplies SR-17018 as a precision powder in three sizes — 1 g, 5 g, and 20 g — with a certificate of analysis issued for every batch. The certificate documents identity confirmation by mass spectrometry and nuclear magnetic resonance, purity by high-performance liquid chromatography, and assay concentration against a reference standard.

Our internal specification is ≥ 99% by HPLC, above the ≥ 98% minimum that has historically been common in the research-reagent market for this compound. Batches that fall below 99% are not released for sale. See the safety and handling guide for storage, stock-solution preparation, and PPE recommendations.

Tablet formats and custom formulations are not currently offered. Bulk quantities beyond 20 g are available by request; contact us through the site for lead time and pricing.

Is SR-17018 a controlled substance? As of the last review date at the top of this page, SR-17018 is not scheduled under the US Controlled Substances Act and is not listed as a controlled substance in the major international research-chemical schedules we track. Regulatory status varies by jurisdiction and is updated more often than page reviews; laboratory managers are responsible for confirming current classification before receipt.

Is SR-17018 the same molecule as oliceridine (TRV130)? No. The two are distinct chemical entities developed by different groups. Both are biased MOR agonists, but SR-17018 shows a substantially higher bias factor in the Schmid 2017 dataset, and it has not been developed as a clinical drug.

Who first synthesized SR-17018? The compound was first reported in the 2017 Cell paper from the Bohn laboratory at Scripps Research. The medicinal-chemistry effort was led by Thomas Bannister and colleagues in the Scripps drug-discovery department.^[1]

Can SR-17018 be used in humans? No. SR-17018 is not approved for human use and has not entered human clinical trials. It remains a preclinical research compound.