Medical cannabis and cancer

What cancer is

Cancer is not one disease but more than 200, grouped by the tissue and cell type where abnormal growth begins — carcinoma, sarcoma, leukaemia, lymphoma, myeloma, and central nervous system cancers. The common feature is uncontrolled cell division that can invade nearby tissue and, in many cases, spread to distant sites through the blood or lymphatic system (metastasis).

In the UK, around 393,000 new cancer cases were diagnosed in 2021. The most common cancers in UK adults are breast, prostate, lung, and bowel. Treatment typically involves one or more of surgery, radiotherapy, chemotherapy, targeted therapy, immunotherapy, and hormone therapy. For advanced or metastatic disease, the focus often shifts from cure to symptom control and quality of life.

The research on cannabis and cancer splits into two distinct questions: whether cannabinoids can help manage cancer symptoms and treatment side effects (pain, nausea, appetite loss, anxiety), and whether they can affect the cancer itself (anti-tumour effects). These two lines of evidence come from different study types and carry different levels of certainty. This page addresses both, in that order.

Cannabis research on Cancer

Symptom management

A 2010 multicentre, double-blind, randomised, placebo-controlled, parallel-group trial of a THC:CBD oromucosal spray (nabiximols) and a THC-only extract in 177 patients with advanced cancer pain inadequately controlled by opioids found that the THC:CBD extract produced a statistically significant reduction in pain compared with placebo, while the THC-only extract did not separate from placebo on the primary endpoint (human RCT, n=177). The THC:CBD group showed a treatment difference of -0.61 points on a 0-10 numerical rating scale (P=0.014). The THC-only group showed a difference of -0.33 points, which was not significant (P=0.245). The study was published before nabiximols was licensed in the UK for multiple sclerosis spasticity, not for cancer pain.

A 2023 Cochrane Review (Hauser et al., 2023) assessed cannabis-based medicines for adults with cancer pain (Cochrane systematic review). It concluded that the evidence base is limited and that the available trials are small. A 2021 systematic review and meta-analysis in the BMJ (Wang et al., 2021) pooled randomised trial data on medical cannabis for chronic non-cancer and cancer-related pain (systematic review and meta-analysis). The analysis included both pain populations; results specific to cancer pain were not reported separately.

Two synthetic cannabinoids, nabilone and dronabinol (synthetic THC), are licensed in the UK for chemotherapy-induced nausea and vomiting that has not responded to conventional antiemetics. Both were studied in RCTs conducted largely in the 1980s against older comparators such as prochlorperazine. No RCT has compared nabilone or dronabinol directly against modern 5-HT3 antagonists such as ondansetron. See the MCPH page on chemotherapy-induced nausea for the full evidence breakdown.

A 2015 continuing-education review in CA: A Cancer Journal for Clinicians (Kramer, 2015) examined the available evidence for medical cannabis in cancer and concluded that dronabinol is the best-studied cannabinoid for chemotherapy-induced nausea and anorexia with weight loss. The review also described what the evidence does not establish: that cannabis is used for the cancer itself (narrative review).

A 2016 user’s-guide review by Maida and Daeninck in Current Oncology summarised the practical evidence for cannabinoid therapies in oncology, including pain, nausea, appetite, and sleep. It described the evidence as emerging and incomplete (narrative review).

A perspective article by Guzman (2018) in Cannabis and Cannabinoid Research argued that the controlled clinical trials supporting medical cannabis for cancer symptoms have mostly been conducted with purified cannabinoid preparations rather than herbal cannabis, and that the evidence for symptom relief, while real, is less robust than sometimes portrayed (expert perspective).

Anti-tumour effects

It consists of in vitro cell-line studies and animal experiments.

A 2009 review by Guzman and colleagues (Pharmacological Research) examined endocannabinoid system modulation in cancer biology and therapy. It described preclinical findings that cannabinoids inhibit tumour cell proliferation, migration, and angiogenesis in cell cultures and animal models, primarily through CB1 and CB2 receptor-dependent mechanisms. The review noted that “the available data remain limited and sometimes contradictory” and that “none of the cannabinoid-related medicines available at present is used as an anti-tumour agent in clinical practice” (narrative review, 2009).

A 2013 critical appraisal by Cridge and Rosengren reviewed the literature on cannabinoids as anticancer agents. It catalogued preclinical studies showing that cannabinoids induce apoptosis (programmed cell death) in glioma, breast, prostate, thyroid, colon, skin, and pancreatic cancer cell lines. The review noted that most findings are from cell cultures and animal models, that some cancer cell lines are resistant to cannabinoid-induced death, and that under some conditions cannabinoids may promote proliferation rather than inhibit it (narrative review, 2013).

• De Petrocellis et al. (1998) reported that the endogenous cannabinoid anandamide inhibited human breast cancer cell proliferation in vitro, with IC50 values between 0.5 and 1.5 microM and 83-92% maximal inhibition at 5-10 microM (cell culture study, 1998).

• Greenhough et al. (2007) found that THC inhibited RAS-MAPK and PI3K-AKT survival signalling and induced BAD-mediated apoptosis in colorectal cancer cells (cell culture study, 2007).

• Preet et al. (2008) reported that THC inhibited epidermal growth factor-induced lung cancer cell migration in vitro and reduced tumour growth and metastasis in a mouse model (cell culture and animal study, 2008).

• Massi et al. (2004) found that CBD reduced mitochondrial oxidative metabolism and induced apoptosis in U87 and U373 human glioma cell lines (cell culture study, 2004).

• Andradas et al. (2011) reported that the putative cannabinoid receptor GPR55 promotes cancer cell proliferation in vitro, and that its expression is upregulated in human tumours compared with matched normal tissue (cell culture and human tissue study).

A 2005 epidemiologic review by Hashibe and colleagues examined two cohort studies and 14 case-control studies on marijuana use and cancer risk and concluded that the available studies did not show a consistent positive association between cannabis smoking and tobacco-related cancers, but that the evidence was limited by small numbers of heavy users and inadequate long-term follow-up (epidemiologic review, 2005).

Compounds studied for Cancer

THC is the cannabinoid with the most direct human evidence for cancer-related symptom relief. Two licensed synthetic THC medicines, dronabinol and nabilone, are indicated in the UK for chemotherapy-induced nausea and vomiting unresponsive to conventional antiemetics. A THC:CBD combination spray improved cancer pain scores relative to placebo in one multicentre RCT (n=177), though THC alone did not separate from placebo. Preclinical anti-tumour data exist for THC in colorectal, lung, breast, and glioma cell lines, but no human trial has tested THC as a cancer treatment.

CBD was a component of the THC:CBD spray that showed a statistically significant pain reduction in the 2010 cancer-pain RCT. CBD has not been tested alone in a human cancer-pain or anti-tumour RCT. Preclinical studies in glioma cell lines and animal models show that CBD inhibits tumour cell proliferation and induces apoptosis.

CBG has preclinical anti-tumour data in some cell lines, but no human RCT has tested CBG for any cancer-related outcome.

A 2016 human trial of THCV was conducted in type 2 diabetes, not cancer.

Beta-caryophyllene is a CB2 receptor agonist. CB2 receptors are expressed on immune cells and some tumour cells, and CB2 activation has been linked to anti-inflammatory and possible anti-tumour effects in preclinical models. No human cancer trial of beta-caryophyllene exists.

Pinene has demonstrated anti-inflammatory effects in cell and animal models. Preclinical data suggest pinene may also inhibit acetylcholinesterase activity, though this has not been tested in cancer-related cognitive impairment. No human cancer trial of pinene exists.

Limits of the evidence for Cancer

What the evidence establishes

Synthetic THC (dronabinol, nabilone) is licensed in the UK for chemotherapy-induced nausea and vomiting unresponsive to conventional antiemetics. This is supported by RCT evidence, though the comparator drugs used in those trials are not current standard-of-care antiemetics.

A THC:CBD oromucosal spray reduced cancer pain relative to placebo in one multicentre RCT (n=177). The THC-only arm did not separate from placebo on the primary endpoint.

Cannabinoids induce apoptosis and inhibit proliferation, migration, and angiogenesis in multiple human cancer cell lines and animal models. This is a reproducible preclinical finding across glioma, breast, colorectal, lung, prostate, thyroid, pancreatic, and skin cancer cell lines.

What the evidence does not establish

That cannabis, cannabinoids, or cannabis-based medicines treat cancer in humans. No RCT has tested whether any cannabinoid shrinks a human tumour, extends progression-free survival, or improves overall survival in any cancer type. The anti-tumour evidence is entirely preclinical.

That cannabis is more effective than, or as effective as, standard cancer treatments. No comparative trial exists for surgery, radiotherapy, chemotherapy, targeted therapy, or immunotherapy.

That smoking cannabis is a safe delivery method for people with cancer. Cannabis smoke contains many of the same carcinogens as tobacco smoke, and heavy cannabis smoking has been associated with respiratory symptoms, though the epidemiologic evidence for a causal link to lung or head-and-neck cancer is inconsistent and limited.

That a specific cannabinoid ratio or terpene profile improves cancer outcomes. The preclinical evidence is almost entirely conducted with isolated compounds at concentrations that may not be achievable in human tissue through typical consumption.

The long-term effects of regular cannabinoid use in cancer patients on treatment response, drug metabolism, immune function, and survival are largely unknown.

Related conditions

• Chemotherapy-induced nausea ; nabilone trials and current antiemetic guidance
• Palliative care ; limited trials covering appetite, pain and nausea
• Chronic pain (NICE context) ; the evidence behind NICE guideline NG144
• HIV/AIDS ; clinical research on symptom and medication side-effect management

Read next

• THC ; intratumoural pilot trial and cell-culture apoptosis findings
• CBD ; glioma xenograft and breast cancer cell preclinical data
• Browse the cannabinoid reference

Sources

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