Respiratory depression with concomitant use of opioids and cannabinoids: a case report

The United States has had a 15-fold increase in daily cannabis use in the last 30 years. There is a growing importance for palliative care physicians to understand the pharmacological interactions between high-dose opioids and cannabinoids when treating patients with cancer-related pain who are increasingly concomitantly using cannabinoids. We present a case of respiratory depression following high‑dose THC and opioids. We discuss proposed mechanistic interactions, the importance of cannabinoid use in social history, and the role of proactive counseling of patients with concomitant use.

A middle-aged patient with metastatic stage IV rhabdomyosarcoma presented to the hospital for management of abdominal distension and severe pain. Palliative care was consulted for cancer-related pain management and goals-of-care conversation. Hydromorphone patient-controlled analgesia (PCA) was started along with methadone on the second day. Following a goals-of-care discussion regarding the terminal prognosis, the patient independently took 100 mg THC/CBD tincture to manage anxious emotions. Later that evening, the patient developed bradypnea and unresponsiveness, recovering fully after two administrations of naloxone. After a brief intermission, PCA was increased without further respiratory depression despite overall higher morphine equivalent daily dose.

In our case, we describe how 100 mg cannabinoid product was a contributing factor in acute opioid toxicity possibly due to active inhibition of UGT2B7 (UDP-glucuronosyltransferase 2B7), a liver enzyme crucial in the metabolism of morphine. For patients who use cannabis, explicit counseling regarding the risks of combining high-dose opioids with high-dose cannabinoids is needed. Proactive counseling with patients in this changing landscape of cannabinoid use will become essential for their safety in the treatment of cancer-related pain.