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β-arrestins play pivotal roles in seven transmembrane receptor (7TMR) signalling and trafficking. To study their functional role in regulating specific receptor systems, current research relies mainly on genetic tools, as few pharmacological options are available. To address this issue, we designed and synthesised a novel lipidated phosphomimetic peptide inhibitor targeting β-arrestins, called ARIP, which was developed based on the C-terminal tail (A343-S371) of the vasopressin V2 receptor. As the V2R sequence has been shown to bind β-arrestins with high affinity, we added an N-terminal palmitate residue to allow membrane tethering and cell entry. Here, using BRET2-based biosensors, we demonstrated the ability of ARIP to inhibit agonist-induced β-arrestin recruitment on a series of 7TMRs that includes both stable and transient β-arrestin binders, with efficiencies that depend on receptor type. In addition, we showed that ARIP was unable to recruit β-arrestins to the cell membrane by itself, and that it did not interfere with G protein signalling. Molecular modelling studies also revealed that ARIP binds β-arrestins as does V2Rpp, the phosphorylated peptide derived from V2R, and that replacing the p-Ser and p-Thr residues of V2Rpp with Glu residues does not alter ARIP’s inhibitory activity on β-arrestin recruitment. Importantly, ARIP exerted an opioid-sparing effect in vivo, as intrathecal injection of ARIP potentiated morphine’s analgesic effect in the tail-flick test, consistent with previous findings of genetic inhibition of β-arrestins. ARIP therefore represents a promising pharmacological tool for investigating the fine-tuning roles of β-arrestins in 7TMR-driven pathophysiological processes.