Lancet Review Examines Three Cannabis-Cancer Links: Causing, Fighting, and Treating Cancer Symptoms | Research

The takeaway

A Lancet Oncology review found inconsistent evidence on whether smoking cannabis causes cancer, mixed lab results on cannabinoid anti-tumor effects, and reasonable evidence that THC helps manage cancer symptoms like nausea, appetite loss, and neuropathic pain.

Read this if you want to understand what was known about the relationship between cannabis and cancer, from both risk and treatment perspectives.

Three distinct cannabis-cancer relationships examined: causation (inconsistent), anti-tumor (mixed), symptom management (positive)

What the researchers found

This review addressed three distinct relationships between cannabinoids and cancer.

First, regarding cancer causation: case reports linked cannabis smoking to upper respiratory tract cancers in young adults, but epidemiological evidence from cohort and case-control studies was inconsistent.

Second, regarding anti-tumor effects: some lab studies showed THC and synthetic cannabinoids had antineoplastic effects, while others showed THC impaired immune responses to cancer. No evidence existed that cannabinoids have anticancer effects in humans.

Third, regarding symptom management: evidence supported THC for improving appetite, reducing nausea and vomiting, and alleviating moderate neuropathic pain in cancer patients. The main challenge was developing safe delivery methods that provide therapeutic effects without adverse psychoactive effects.

Why it matters

This review separated three commonly conflated questions about cannabis and cancer into distinct evidence evaluations. The distinction between cannabis potentially causing cancer through smoking, potentially fighting cancer at the cellular level, and treating cancer symptoms is critical for informed decision-making.

The numbers in context

Three relationships examined: causation (inconsistent evidence), anti-tumor effects (mixed in vitro/in vivo, none in humans), and symptom management (positive evidence for appetite, nausea, neuropathic pain).

How the study worked

Narrative review published in The Lancet Oncology examining three categories of evidence: epidemiological studies on cannabis smoking and cancer risk, preclinical studies on cannabinoid anti-tumor effects, and clinical evidence on symptom management in cancer patients.

What this study cannot tell us

Epidemiological evidence on cancer causation was limited and inconsistent at the time. Anti-tumor evidence was entirely preclinical with contradictory findings. The review was narrative rather than systematic.

How to read the evidence

Review published in a high-impact oncology journal. Provides a balanced assessment but notes the limited and inconsistent nature of the evidence base at the time.

When this study was published

Published in 2005 in The Lancet Oncology. Subsequent epidemiological and preclinical research has expanded the evidence base, though many questions remain.

The bigger picture

The review noted that in US public debate, advocates for medical cannabis use sometimes argued for smoked cannabis rather than pharmaceutical cannabinoids, which conflated potential cancer risks from smoking with the therapeutic benefits of cannabinoids. This distinction between the plant and its active compounds remains relevant.

Questions still open

Do non-smoked cannabinoid delivery methods eliminate any cancer risk while preserving therapeutic benefits? Will preclinical anti-tumor effects translate to human cancer treatment?

Common questions

Does smoking cannabis cause cancer?

As of this 2005 review, the evidence was inconsistent. Case reports linked cannabis smoking to upper respiratory cancers in young adults, but larger epidemiological studies gave mixed results. The question remains actively studied.

Can cannabis cure cancer?

No evidence supported this in humans as of 2005. Some laboratory studies showed anti-tumor effects of THC and synthetic cannabinoids, but others showed THC could impair immune responses to cancer. Clinical evidence was limited to symptom management, not cancer treatment itself.

Read the original research

Cannabinoids and cancer: causation, remediation, and palliation.

The Lancet. Oncology, 6(1), 35-42

View on PubMed ↗

Citation

Hall, Wayne; Christie, MacDonald; Currow, David. (2005). Cannabinoids and cancer: causation, remediation, and palliation.. The Lancet. Oncology, 6(1), 35-42.