This study explores the rise of a fentanyl smoking culture in San Francisco, focusing on the transition from injection to smoking due to difficulty injecting and fear of overdose. Fentanyl is extremely cheap ($10/gram) but varies in quality. Common smoking materials include foil, glass bubbles, bongs, and dabbing devices. Participants gauge potency through inhalation and develop techniques to regulate dosage. Smoking is social, with shared equipment and drugs, but concerns about hygiene and overdose risk from shared equipment persist. Fentanyl residue accumulates on smoking materials and is often shared, traded, or stolen, posing a new overdose risk. Participants report high daily fentanyl consumption (up to 50 mg/day), with some smoking up to three grams per session. Smoking is seen as less risky than injecting, but substantial uncertainty remains. Despite this, San Francisco overdose mortality reached a record high in 2023. Recommendations include pacing, awareness of dosages, and checking tolerance of residue recipients to reduce overdose risks. The study highlights the need for further exploration of interventions to reduce fentanyl smoking overdose risks. The rise of fentanyl smoking reflects both innovation and adaptation in drug use, with implications for public health.This study explores the rise of a fentanyl smoking culture in San Francisco, focusing on the transition from injection to smoking due to difficulty injecting and fear of overdose. Fentanyl is extremely cheap ($10/gram) but varies in quality. Common smoking materials include foil, glass bubbles, bongs, and dabbing devices. Participants gauge potency through inhalation and develop techniques to regulate dosage. Smoking is social, with shared equipment and drugs, but concerns about hygiene and overdose risk from shared equipment persist. Fentanyl residue accumulates on smoking materials and is often shared, traded, or stolen, posing a new overdose risk. Participants report high daily fentanyl consumption (up to 50 mg/day), with some smoking up to three grams per session. Smoking is seen as less risky than injecting, but substantial uncertainty remains. Despite this, San Francisco overdose mortality reached a record high in 2023. Recommendations include pacing, awareness of dosages, and checking tolerance of residue recipients to reduce overdose risks. The study highlights the need for further exploration of interventions to reduce fentanyl smoking overdose risks. The rise of fentanyl smoking reflects both innovation and adaptation in drug use, with implications for public health.