INI-4001 is a TLR7/8 agonist, with EC 50 values of 1.89 μM and 4.86 μM for TLR7/8 , respectively. INI-4001 induces signaling and SEAP production through TLR7 and TLR8. INI-4001 promotes the generation of high-affinity, specific antibodies against fentanyl, preventing fentanyl from crossing the blood-brain barrier, making it an effective adjuvant for fentanyl vaccines in the opioid use disorder (OUD) population.