Reference summary — not medical advice or a personal risk estimate.
Opium consumption
Quick answer
Classified as Group 1 — carcinogenic to humans, based on sufficient evidence in humans. Smoked, eaten, or used as a tea. Long-term use is most common in parts of Iran, Afghanistan, and surrounding regions.
Summary
Long-term opium use is associated with multiple cancers.
Detail
Opium consumption is Group 1 with sufficient evidence for cancers of the lung, urinary bladder and larynx, and limited evidence for esophageal and pancreatic cancers. Use is most common in parts of Iran, Afghanistan and surrounding regions.
What's not established
This classification is based on sufficient evidence in humans that this factor can cause cancer. It does not establish a safe exposure threshold, your personal risk, or how this factor's risk compares in size to other Group 1 agents — hazard classifications are not ranked by magnitude.
Regional relevance
global
Documented in these products
Presence in a product category doesn't imply the product causes cancer. Click each to see the source and context.
Evidence sources
Every claim on this page traces back to one of these. Click through to read the primary document yourself.
Primary sources
IARC
IARC Monographs — Classifications by Cancer Site, Vols 1–140
Supporting sources
ACS
ACS — Known and Probable Human Carcinogens
NTP
NTP — Report on Carcinogens (US National Toxicology Program)
WCRF/AICR
WCRF/AICR — Diet, Nutrition, Physical Activity and Cancer: a Global Perspective (Third Expert Report)
WCRF/AICR
WCRF — Cancer Prevention Recommendations
Last reviewed: October 2026
Official reference list
A government list some readers use alongside the primary evidence. Meyron is not affiliated with it. A chemical being listed does not by itself describe a risk from any particular product.
- California Prop 65 list
State of California's list of chemicals known to cause cancer or reproductive harm.