Decoding Cannabis: Can cannabis suppress tumour growth?

We’ve all heard them. Those somewhat persuasive claims floating around the web of high-dose THC oil shrinking tumours, social media testimonials declaring cannabis as a cancer cure, and not-so-whispered tales of miraculous cancer turnarounds.

These narratives are more than quite powerful, especially when shared (or read) by people facing some of the hardest moments of their lives.

Our goal: clarity, not false hope

We are not here to call anybody a liar.  

Anecdotal evidence is important, but when it comes to something as serious as finding a cure for cancer, it simply cannot replace peer-reviewed clinical research involving human participants. The very last thing we would ever want to do is take hope away. 

In fact, this blog is here to do the exact opposite - to lay out the most recent research into medical cannabis for tumour suppression, compare it to other natural alternatives, and do so in a way that is easily accessible for anyone interested. 

When there’s a big gap between anecdotal experience and scientific evidence, and existing in that space is a healthy dose of confusion, obvious contradiction, and the potential for false certainty, it becomes even more important to look closely at what the science says, and what it doesn't.

But before we go on, let’s make one thing crystal clear. As of now, there is just not enough peer-reviewed research to make any claims about the efficacy of cannabis in cancer tumour suppression.

Yes, medical cannabis for cancer symptoms and treatment-related side effects control is already proven - things like vomiting and nausea, appetite loss, sleep disruption, cancer pain, and cancer-related anxiety/depression. That’s what the clinical evidence supports, and it’s how medical cannabis is being prescribed for cancer patients in the UK right now. 

But taking cannabis to actively treat or reduce the size of a tumour? 

That’s a completely different conversation. 

One that’s still unfolding in preclinical labs, early-phase studies, and cautious scientific reviews. 

Are some of the emerging results promising? 

They are, but it’s early days. The results are nowhere near conclusive.

So let’s talk about what we actually do know.

Medical cannabis research is expanding beyond cancer symptom relief

Welcome back to Decoding Cannabis, our weekly blog series where we usually take one of the more recent studies on cannabis and break it down into something clear, human, and a little more approachable than your average journal paper. 

This time, we're actually going to focus on two recent peer-reviewed studies to make sure things stay balanced. 

The first, Use of Cannabis and Cannabinoids for the Treatment of Cancer, has a close look at how compounds like THC and CBD act in lab-based cancer models, including how they might trigger cancer cells to self-destruct, slow tumour growth, and block the blood supply tumours need to survive.

The second, Herbal Therapies for Cancer Treatment, doesn’t mention cannabis at all. It focuses on a pretty extensive range of plant compounds (like curcumin, ginseng, and EGCG) that have long been studied not only for their potential to slow or suppress cancer, but also to support the body alongside conventional treatment. Including this review helps place cannabis in context. It’s one of many natural substances under investigation, not a lone outlier.

What we’re looking at is not proof, but, a sprinkling of possibility.

Research into how cannabis might affect tumours is in the early stages

We’re still in the early days of understanding what cannabis might do when it comes to tumour growth. 

The research is, no doubt, fascinating - but, is it robust?

Is the evidence strong?

Not yet. 

The few human trials that do exist are small and early-stage, and the results aren’t always consistent. What’s actually being studied also matters - different types of cannabinoids, different doses, and different cancers can all produce very different outcomes.

Too often, we see cancer lumped together as one ‘condition’, but it’s not. That means a finding that looks promising in one type of cancer often does not apply to another at all. 

Cannabinoids and cancer: What does the latest research say?

The 2022 review by Cherkasova and colleagues takes a broad but careful look at how cannabinoids and cancer treatment might interact. It not only looked at the findings from Cannabis sativa L. derived cannabinoids like THC and CBD, but also lab-made synthetic cannabinoids.

What types of cancer were studied?

• Glioma (a type of brain cancer), which shows higher levels of cannabinoid receptors
• Breast and lung cancer, partly because they’re common and easier to study in the lab
• Pancreatic, prostate, and melanoma models, though to a lesser extent

Glioma stands out in this review. The presence of CB1 and CB2 receptors (the receptors that cannabinoids mostly interact with) in brain tumours makes it a key focus for cannabinoid research.

What’s happening in the body?

In these early studies, cannabinoids like THC and CBD seem to affect a few of the systems that cancer cells rely on. That includes:

• Helping damaged cells break down and die (apoptosis)
• Slowing the rate at which tumours grow (antiproliferative effects)
• Cutting off the blood supply that feeds a tumour (anti-angiogenesis)
• Making it harder for cancer to spread to new areas (inhibition of metastasis)

Can cannabis make chemo or radiotherapy work better?

Some of the research looked at whether cannabinoids might be used alongside existing cancer treatments:

• In glioma, THC (or a synthetic version called Sativex) seemed to help chemotherapy drugs like temozolomide work more effectively in mice.

• A double-blind study tested Sativex in conjunction with temozolomide. Overall, the 1-year survival rates were higher in patients taking Sativex (83%) compared to the placebo group (44%).
  
  

But this area is still unclear. 

We know that cannabinoids can and do interact with other medications, sometimes in quite unexpected ways. This only strengthens the point that much more research is needed before anything close to concrete claims can be made regarding the efficacy of cannabis for cancer suppression. 

What about cannabis for cancer symptom management or treatment-related issues?

This is where cannabis has the strongest footing in clinical research, not just in this review, but in many studies stretching back more than a decade.

The review includes a large observational study of almost 3,000 cancer patients (average age 59.5) that tracked symptom relief over six months of cannabis treatment. Patients reported improvements in:

• Pain
• Anxiety
• Nausea
• Appetite loss
• Sleep disruption
• Depression

Medical cannabis treatment was shown to be well tolerated among all age groups, but particularly in patients in palliative care situations. When side effects did appear, they were usually mild and tended to fade on their own without the need for treatment.

It’s a finding that resonates with many patients already prescribed UK medical cannabis for cancer support. 

The review also highlights real-world registry data showing that people respond in different ways. Age, sex, and the type of CBPM administered all seem to shape how much relief someone experiences.

• Women were more likely to report improvements in nausea, appetite, and drowsiness.
• Men appeared to respond more to THC-dominant products for pain control.
• Older adults are using medical cannabis more frequently, though evidence remains limited in this age group.

But thanks in large part to cotton industry lobbyists pressuring Western governments to outlaw hemp, cannabis became a convenient scapegoat villain. Its reputation unravelled slowly at first, then all at once. Medical use faded. Scientific inquiry was blocked at the gate.

For decades, researchers trying to study cannabis ran into brick walls. We are talking about laws that simply didn’t make sense, approval processes that dragged on for years, and funding bodies that steered clear altogether. Even getting hold of consistent, study-grade cannabis was a task in itself.

That’s finally starting to change. 

The stigma is slowly fading, and with it comes greater access for scientists to finally start really cracking on with the important research. That said, medical research is anything but a sprint. It’s a slow process, one that sometimes involves years of planning and permissions, then patient recruitment, follow-ups, analysis, publication, peer-reviewing - a mountain of paperwork and hoops to jump through.

So while things are moving in the right direction, the science is still playing catch-up. 

The studies we do have are encouraging, but there’s a long way to go before we can speak with any certainty. Until then, cannabis remains just one of many areas of research for tumour suppression, not a confirmed treatment.

What do scientists still need to figure out?

The review ends by highlighting key unanswered questions:

• Which types of cannabinoids help with which types of cancer?
• Do the effects depend on activating certain receptors, like CB1 or CB2?
• How does cannabis affect other cancer drugs?
• Is it safe and effective over the long term?
• How do sex, gender, and age change outcomes?

These are the questions researchers are now trying to answer. Until they do, cannabinoids remain a promising area of study, but they should never be promoted as a cure for cancer.

How do natural cancer treatments compare to cannabis in research?

Cannabis isn’t the only plant that scientists are looking at. A recent review from 2023 looked at other plant-derived compounds that have long been part of traditional medicine and are now being studied as natural cancer treatment options.

Which natural compounds are being studied for cancer?

The study looked at a wide range of plant-based compounds, many of which have been used for centuries in traditional/folk medicine. Each one has shown some potential in lab and animal studies to influence how cancer behaves, whether by slowing its growth, cutting off its blood supply, or encouraging damaged cells to die off.

Curcumin (turmeric)

Curcumin showed promise in slowing tumour growth in breast, bowel, prostate, and pancreatic cancer models. It has also been proven to help reduce inflammation and may help trigger cancer cell death.

Resveratrol (red grapes)

Resveratrol blocked new blood vessels from feeding tumours and may slow the spread of cancer cells. Most studies of resveratrol focused on breast and prostate cancer models.

EGCG (green tea)

ECCG seemed to stimulate damaged cells to shut down in skin, lung, and breast cancer studies. It also may target key genes that help cells repair or divide.

Boswellic acid (frankincense)

Boswellic acid showed potential in reducing the rate of tumour growth in some brain and blood cancers, especially glioma and leukaemia, but the mechanisms behind these findings are not well understood yet.

Quercetin (onions and berries)

Quercetin disrupted how cancer cells multiply in colon, breast, and lung models. It may also help calm oxidative stress around the tumour, creating a less favourable environment for growth.

Lycopene (tomatoes and watermelon)

Lycopene was linked to slower tumour development in prostate and stomach cancer. Its antioxidant activity is thought to be key, but more research is needed to confirm such findings.

Ginsenosides (ginseng)

Early studies in liver and lung cancer suggest ginsenosides may help reduce inflammation and limit how quickly tumour cells multiply.

Silibinin (milk thistle) 

Silibinin was shown to reduce tumour size and blood flow in prostate, colon, and skin cancer models, and may also help trigger cancer cell death in some cases.

Do these natural treatments face the same limitations as cannabis?

100%.

As with cannabis, the vast majority of the studies available right now come from lab studies or research involving animal subjects, just as with cannabis. And, just as with cannabis, this means we simply don’t have a full, scientifically based understanding of how well they actually perform the above-listed potential benefits in humans. 

The takeaway is that cannabis is not unusual in the phytochemical sphere for cancer treatment. 

It sits alongside many other plant-based treatments being tested for similar reasons. Seeing it in that wider group helps us keep things in perspective - not overhyping, not dismissing, just paying attention.

What about Rick Simpson Oil (RSO) for cancer suppression?

Rick Simpson Oil (often simplified to RSO) is far too often promoted as a natural cancer cure. But the evidence just isn’t there yet. Most of what we know comes from personal stories, not clinical trials.

While it’s easy to find bold, clickbaity claims online, we need far more research before RSO can be thought of as a cancer treatment option.

Why Rick Simpson Oil is not prescribed by UK clinics

Cannabis-based medicines must meet strict safety and evidence standards to be prescribed. Our research suggests that no company has produced an RSO product to the UK's stringent standards yet.

That doesn’t mean people’s stories don’t matter. It just means clinics like Releaf can’t prescribe something that hasn’t been through proper testing. In a space full of noise, clarity matters. This is about protecting patients, not dismissing them.

That’s not to say RSO will never play a role in future care. But right now, it sits outside the bounds of regulated medical cannabis in the UK.

We ask Releaf’s Medical Director and resident oncology specialist, Dr. Sue Clenton, for her thoughts…

“Cannabis is well known to provide relief from many of the symptoms associated with cancer and its treatments. We have many patients here at Releaf who benefit from reductions in pain, anxiety and nausea, and vomiting.  We also help with mood and poor appetite.  

The jury is still out on the use of cannabis as an anti-cancer agent, however, and we watch any emerging evidence closely.  

We will always analyse data and provide reliable information to our patients, while continuing to hope that positive research will come soon and allow cannabis to be used in a wider way in cancer care.  For now, we will continue to prescribe responsibly and for conditions/symptoms it has been proven to help with.”

Real patient experiences with UK medical cannabis for cancer

Across the UK, cancer patients who have signed up with Releaf are already being prescribed cannabis to manage pain, nausea, anxiety, sleep loss, and more. These stories don’t claim to cure, but they offer something else. A glimpse of what relief looks like in the real world. Quiet, honest progress. Sometimes that's enough to matter.

Louise’s story: Cancer, courage, and compassionate treatments

For Louise, everything shifted in April 2022 when she found a lump on her chest.

What followed was a blur of scans, surgeries, treatment plans, and setbacks. Plans she’d made for her life, including her wedding, had to be put on hold as recovery took centre stage. In 2024, worn out from the cycle and looking for something gentler to support her through it all, she found Releaf.

“It's all about treating the side effects, as well as cutting down on all the prescribed meds, because I've been taking them for two and a half years now, and I just like I need a break. I just need a moment to try to process the last two and a half years. That’s why I came to Releaf in the first place.

Every time I've gone to see my oncologist, the results of every test have never been what was expected. Never. Especially the last time they gave me the all clear. They said my lungs were clear in April, and then literally a month later, they said, “I’m sorry, they're not clear.”  Then my prognosis changed from six to 12 months to three to 12 months. How can the prognosis change like that?

When I first spoke to Dr. Clenton, I liked her from the minute we started speaking, and I felt really comfortable talking to her. I felt like she really knew what she was talking about, and I could trust what she was saying, because she was asking all the right questions. I knew she wasn't going to give me a treatment that was going to make me feel awful straight away. 

Dr. Clenton and I chatted for at least half an hour, and she never once made me feel rushed, or like she needed to go and deal with other things, she was focused only on me. The second time I spoke to her, she remembered me and said, “Hello Louise! Nice to speak to you again.” I was very impressed by that. She must talk to hundreds of people, and for her to remember me and call me by name felt a lot different from my experiences with other doctors….

I only use the medical cannabis oil, and for now, it’s working. The oil really works for my side effects.

The first big change that I noticed was my sleep. It seemed to calm my mind and helped me sleep much better at night. I used to take the antianxiety tablet Lorazepam at night to sleep, and I'm not taking those any more. Lorazepam was something I never really wanted to take because it can be an addictive medication.”

Patients deserve clear, well-researched, and compassionate guidance on UK medical cannabis for cancer 

The research into cannabis as a cure for cancer may not be anywhere near conclusive just yet, but the body of research is growing, and with it, our understanding of the potential (and limitations) of medical cannabis for cancer.

At Releaf, we believe patients deserve information that’s not only clear but also responsible. That means staying grounded in the evidence, being upfront about what we know and what we don’t, and never trading honesty for hype.

Medical cannabis is already helping people living with cancer sleep better, feel less pain, eat more, and cope with the emotional weight of treatment. These are not small things - in fact, they often make a world of difference for patients going through cancer treatment.

If you (or a loved one) is interested in learning more about UK medical cannabis for cancer (or any other chronic health issues), head to our medical cannabis eligibility checker. It takes less than 20 seconds to complete, is totally confidential, and completely free.