Endogenous Opioid Response to Injections

Inclusion Criteria:

* Capable of understanding and providing consent in English and capable of complying with the outcome instruments used
* ≥3 months low back pain with persistent limiting symptoms despite conventional treatment (physical therapy and oral medications)
* Low back pain NRS ≥ 4/10 in intensity on 7-day average and at time of lumbar medial branch block

Exclusion Criteria:

* Daily use of opioid medications or recreational drugs, or if using opioids PRN, report of opioid use within the 3 days prior to participating in the protocol
* Positive urine drug screen for opioid medication on the day of naloxone administration
* Allergy to naloxone
* Refusal of or failure to place IV
* Previous LMBB or LMBRN
* Known spine condition that may affect the ability to diagnose or treat facet pain or lead to spine surgery (e.g. instability, severe spinal stenosis, radiculopathy, previous spine operation resulting in alteration of anatomy targeted by LMBB or LMBRFN)
* Active medical condition that would limit the safety of naloxone administration (e.g. severe kidney or liver failure, unstable cardiac disease, infection, severe coagulopathy)
* Psychiatric, medical, neurologic, or pain-related disorder that may compromise the ability of the patient to accurately report changes in low back pain
* Requirement for procedural sedation to tolerate LMBB