Chronic low back pain is a common and disabling condition that affects millions of people in the United States. Many people with chronic low back pain do not get enough relief from current treatments. Cannabis may help reduce pain, but researchers do not fully understand how it affects the brain in people with chronic pain. The purpose of this study is to examine how inhaled cannabis changes brain activity and reduces pain in people with chronic low back pain. Results from this study may help researchers better understand how cannabis works for pain and support the development of improved pain treatments.

Chronic low back pain is one of the most common causes of pain and disability in adults. Unfortunately, treatments that can directly reduce chronic low back pain remain limited. Cannabis has shown promise for pain relief, but researchers do not yet fully understand how it affects the brain or reduces pain in people with chronic pain.

The purpose of this study is to examine how inhaled (vaporized, not smoked) cannabis affects pain responses and brain activity in adults with chronic low back pain. Researchers will compare the effects of cannabis containing tetrahydrocannabinol (THC) to a placebo cannabis containing 0% THC.

This study involves one visit to the Keck Center for Functional MRI at UC San Diego. Participants will complete screening procedures, questionnaires, and pain testing using heat stimulation applied to the calf. Participants will be trained to rate their pain intensity and unpleasantness. A straight leg raise maneuver will also be performed to assess low back pain and any pain radiating down the leg.

Participants will inhale either THC-containing cannabis or placebo cannabis (no THC) using a vaporization device under study staff supervision. Brain imaging, heat pain testing, leg raise assessments, and pain ratings will be collected before and after cannabis administration to evaluate changes in pain processing and brain activity. Researchers will also assess self-reported pain, mood, sleep, stress, and cannabis-related effects using standardized questionnaires.

This study may improve understanding of how cannabis influences the brain and pain systems in people with chronic low back pain, and findings may help support the development of improved treatments for chronic pain.

Inclusion Criteria:

• Between 21-65 years old
• Currently 30 days cannabis free
• Lower back pain for three months or more
• Are not taking opioids
• If female and of a child bearing potential age, are not pregnant or nursing mothers
• Do not have mental or neurological conditions inhibiting sensory/motor functions
• Do not have a lifetime history of dependence on cannabis
• Do not have a lifetime history of DSM-IV schizophrenia, bipolar disorder, panic disorder, or psychosis
• Prior THC-containing cannabis experience within the past two years
• Agrees not to use cannabis outside of the study during participation in the study
• Agrees not to use opioids or barbiturates during participation in the study
• Agrees not to drive a motor vehicle within 4 hours following last use of inhaled cannabis during participation in the study

Exclusion Criteria:

• Active pulmonary disease
• Allergy or past adverse effects or negative past experiences from cannabis
• Positive urine drug test for THC, barbiturates, opioids, oxycodone, or methadone
• Any significant illness, including cardiovascular disease, diabetes, renal and liver disease.
• Any current or history of an immunocompromising disease or condition (such as lupus, psoriasis, multiple sclerosis, etc.)
• Any current or history of neurologic conditions, including Parkinson disease, dementia, cognitive impairment, history of seizure disorder, and history of traumatic brain injury/head injury
• Any current major psychiatric illness, such as bipolar disorder, major depression, psychosis, substance use disorder, or schizophrenia
• Any current or history of suicidal ideation or attempt
• Overt sensitivity to thermal stimulation
• Resting blood pressure > 140/90
• Resting heart rate > 100 beats/minute
• Prisoner
• Institutionalized
• Claustrophobia
• MRI contraindications
• Participation in any new (within 2 weeks prior or any time after enrollment) pain management procedures during the study period
• Known history of vasovagal fainting, syncope, or severe adverse reactions associated with blood draws or needle procedures

Participants and outcome assessor will not be made aware if they are receiving active or placebo marijuana.