The impact of cannabis use on local anesthetic dosing during hair restoration surgery: a case report, proposed mechanisms, and clinical recommendations

Cannabis use has increased significantly in the last decade. This article presents a case where a patient needed more local anesthetic (LA) than usual to induce effective anesthesia during hair transplant surgery. The reason cannabis users often need more LA is poorly understood. One possibility is that cannabis withdrawal effect makes patients more sensitive to pain and stress. Additionally, vasodilatory property of cannabis may speed up LA clearance from the application site. The interactions of two major cannabinoids, cannabidiol (CBD) and tetrahydrocannabinol (THC), with cannabinoid receptor type 1 (CB1), cannabinoid receptor type 2 (CB2), and transient receptor potential vanilloid 1 (TRPV1) receptors are also complex. Furthermore, CBD and THC function as cytochrome P450 enzyme inhibitors potentially impacting systemic metabolism. When planning to administer LA during hair restoration surgery in cannabis users, clinicians should obtain a detailed history of prior consumption (type of cannabis, frequency, dosage). Preoperative planning should consider the anticipated duration of surgery and calculate the maximum safe LA dose to avoid the risk of toxicity. Also, patients should be carefully monitored for vital signs during surgery. If a patient requires frequent re-injection to remain pain free, the surgeon may need to re-assess the surgical plan to avoid toxicity.