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Cannabis and cancer: what the science tells us today
C the Signs
For many people, conversations about cannabis and cancer come from a place of hope - a hope that something natural might ease symptoms or make treatment feel more manageable. For others, it’s a topic filled with uncertainty and mixed messages. With so much information circulating online, it can be difficult to know what’s fact, what’s theory, and what’s still being explored.
What is cannabis?
Cannabis is a plant that has been used for thousands of years, both recreationally and medicinally. The resin it produces contains cannabinoids, chemical compounds that can interact with the human body.
Two of the main cannabinoids are:
- Delta-9-tetrahydrocannabinol (THC) - the compound that causes a “high.”
- Cannabidiol (CBD) - which doesn’t cause a high and is legal in the UK when sold without THC.
The human body naturally produces its own cannabinoids, known as endocannabinoids, which help regulate processes such as appetite, mood and pain. This system is complex and continues to be studied, including how it may relate to certain diseases, cancer among them.
The legal status in the UK
Cannabis remains a Class B drug under UK law, meaning it’s illegal to possess or supply it. However, several prescribed medicines derived from cannabis are approved for use in the NHS, including:
- Nabilone, used to help control nausea and vomiting caused by chemotherapy.
- Epidyolex, used to treat certain types of severe epilepsy.
These are highly regulated medicines, prescribed only when other treatments haven’t worked.
CBD products, such as oils, drops, or gummies, are legal to buy in the UK if they contain no THC and are marketed as food supplements. They cannot legally claim to treat or prevent disease.
What about cannabis oil?
Cannabis oil products vary widely. Some contain only CBD, while others, often sold illegally, include THC. Pure CBD oil is legal to buy as a food supplement in the UK, but products sold online or in shops are not medicines and are not regulated for quality or content.
People living with cancer sometimes explore CBD oil to help with pain, anxiety or sleep. However, claims that CBD or cannabis oil can cure or shrink cancer are not supported by scientific evidence.
If a patient wishes to try CBD, they should always speak to their GP, pharmacist or cancer care team first - especially as CBD can interact with other prescribed medicines.
Cannabis and cancer: what the evidence shows
Researchers around the world have been studying cannabinoids and their potential role in cancer treatment. The results have been mixed and mostly early stage.
Some laboratory studies show that cannabinoids can:
- Trigger cancer cells to die (a process called apoptosis).
- Slow the growth of certain cancer cells.
- Prevent tumours from forming new blood vessels.
However, other studies have found that cannabinoids can:
- Damage healthy blood vessels.
- Sometimes promote cancer cell growth under certain conditions.
It’s also important to note that most of this research has been done in cells in the lab or in animals, not in people. What works in a petri dish doesn’t always translate into safe or effective treatments for patients.
As of 2025, there is no reliable clinical evidence that cannabis or cannabinoids can treat or cure cancer in humans.
What the research is exploring
Recent trials are beginning to look at cannabinoids in controlled, medical settings. These studies focus mainly on symptom control or exploring whether cannabinoids can be safely combined with standard treatment - not on replacing proven therapies.
Medicinal cannabis for symptom control in advanced cancer (2025)
A randomised, double-blind clinical trial tested a cannabis oil against placebo in patients with advanced cancer. The trial found no difference in overall symptom distress, though some patients reported a small reduction in pain. However, this came with higher rates of side effects such as dizziness and fatigue, highlighting the need for further research into safe dosing.
(Hardy et al., 2025).
The ARISTOCRAT trial – UK, ongoing
The ARISTOCRAT trial, led by the University of Leeds and the University of Birmingham, is testing nabiximols (Sativex), a balanced THC:CBD oral spray, alongside standard chemotherapy for people with recurrent glioblastoma. Early data suggests the treatment is well tolerated. The study aims to understand whether adding cannabinoids could improve survival.
(University of Leeds, 2021; The Brain Tumour Charity, 2023; BMC Cancer trial protocol, University of Birmingham, 2023)
Together, these studies show that research is progressing, but there is still no clear evidence that cannabinoids improve cancer outcomes.
What we still need to understand
There are still important questions to answer:
- Which cannabinoids (natural or synthetic) might be most effective?
- What doses are safe and meaningful?
- Which cancer types, if any, might respond?
- How do cannabinoids interact with existing treatments like chemotherapy or immunotherapy?
Until large, well-controlled clinical trials can answer these questions, cannabis cannot be recommended as a cancer treatment.
The bottom line
There’s currently no reliable evidence that cannabis or cannabis oil can treat or cure cancer.
Some cannabinoids may help manage symptoms such as pain, sickness or appetite loss, but always under clinical supervision.
For anyone considering CBD or cannabis-based products, the safest step is to talk to a GP or oncology specialist first. They can help review what’s evidence-based, what’s safe, and what may interfere with ongoing treatment.
Because every informed choice, and every early conversation,gives patients back control, confidence and clarity.
References
Hardy JR, Greer RM, Pelecanos A, et al. (2025). Medicinal cannabis for symptom control in advanced cancer: a double-blind, placebo-controlled, randomised clinical trial of 1:1 tetrahydrocannabinol and cannabidiol. Supportive Care in Cancer. DOI: 10.1007/s00520-025-09763-5
University of Leeds (2021). World-first trial tests cannabis-based drug on aggressive brain tumours. Leeds.ac.uk
The Brain Tumour Charity (2023). ARISTOCRAT: a pioneering trial using a cannabinoid-based drug to treat brain tumours. thebraintumourcharity.org
University of Birmingham (2023). A randomised phase II trial of temozolomide with or without cannabinoids in patients with recurrent glioblastoma (ARISTOCRAT). BMC Cancer protocol. birmingham.ac.uk
Cancer Research UK (2023). Cannabinoids and cancer: what we know. news.cancerresearchuk.org
Helping clinicians see the early clues with confidence
Spotting cancer early is one of the most meaningful moments in healthcare.
Yet it often begins with something small - a feeling that something isn’t quite right, a symptom that could easily be explained by everyday life, or a concern someone has carried for weeks before finding the courage to speak to a doctor. These early clues matter. But they can be incredibly hard to see.
When symptoms hide in plain sight
Many early signs of cancer are vague. Tiredness. A change in appetite. A persistent ache. Things almost everyone experiences at some point.
Clinicians across the world work within tight appointments, large caseloads, and complex diagnostic pathways. In the UK, this often means a doctor has ten minutes to listen, piece together a story, examine, review history, and decide whether more investigation is needed. In other health systems, the pressures look different, but the challenge is the same.
It’s easy to miss the early signals and it’s incredibly human to worry about missing something important.
The emotional side we rarely talk about
Early cancer detection is not just a clinical task - it carries emotional weight. Doctors want to offer reassurance, but they also want to act in time. Balancing those instinctive desires can be exhausting. Many share that the fear of overlooking something serious stays with them long after a consultation ends.
This pressure grows alongside administrative work: navigating referral pathways, coordinating tests, documenting every detail - all while trying to stay present for the next patient who walks through the door. This is why C the Signs exists: to do the heavy lifting in the background so clinicians can focus fully on the person sitting in front of them.
So what does that actually mean?
- Faster recognition of patients who may be at risk
- Clearer, more personalised diagnostic pathways
- More consistent follow-up and thoughtful safety-netting
- More time in appointments for human connection
Independent real-world evaluations have shown meaningful improvements, including fewer emergency cancer diagnoses and quicker routes to early-stage detection. At the centre of every data point is a person whose cancer was found earlier - and whose choices, time, and future were protected.
For clinicians, this support can ease the constant pressure. For patients, it brings earlier answers and a clearer path forward. For healthcare systems, it helps ensure early diagnosis becomes equitable and achievable for all.
Changing the story, one conversation at a time
Cancer is a disease of time - and every day gained matters.
We're just trying to help give some of that time back, transforming what is possible for millions of people and the clinicians who care for them.
Winter fatigue, or something more?
Feeling more tired than usual as winter sets in is common. Shorter days, colder weather, and the rush of everyday life can leave anyone feeling run down. But sometimes, what feels like normal winter fatigue can be something more, and knowing when to check in with your GP can make all the difference.
Why fatigue is common in winter
As daylight hours shorten, many of us feel our energy dip. Lower vitamin D, changes in sleep patterns, and spending more time indoors can all affect how we feel. For most people, this tiredness passes with rest, daylight, and better routines.
But ongoing fatigue, especially when it’s new, persistent, or hard to explain, deserves attention.
When tiredness might signal something else
Tiredness is one of the most common symptoms GPs see, and it can have many causes: stress, anaemia, thyroid issues, infections, or low mood. Occasionally, it can also be an early sign of something more serious, including some cancers.
That doesn’t mean it usually is, but listening to your body and noticing changes early matters.
It’s a good idea to speak to your GP if:
- You feel unusually tired for more than a few weeks.
- You’ve noticed other changes - like weight loss, persistent pain, bloating, or changes in your appetite.
- Your tiredness is getting worse, or affecting your ability to do daily activities.
- Something just doesn’t feel right.
Trust your instinct.
What your GP can do
Your GP is there to help you figure out what’s behind your symptoms. They may:
- Ask questions about your lifestyle, sleep, or stress levels.
- Arrange simple blood tests to check for common causes like anaemia or thyroid issues.
- Discuss whether further investigations or referrals are needed.
Early conversations mean early answers. And if something more serious is found, early detection gives people more time, more choice, and more life.
Taking care of yourself this winter
There are small things you can do that help boost your energy and protect your health:
- Try to get outside for natural light every day, even briefly.
- Keep hydrated and eat regularly - skipping meals can make tiredness worse.
- Move your body in ways that feel good.
- Prioritise rest - recovery is part of productivity.
- Notice changes and speak up early.
The takeaway
Feeling tired in winter is normal. But if the tiredness lingers, feels different, or comes with other changes, don’t ignore it. Checking in early can make a real difference, and sometimes, it can even save a life.
Because when it comes to health, time matters.
Early conversations lead to earlier answers, and earlier answers give people back control, confidence, and choice.
Featured
Why every moment matters: A message from Dr Miles Payling
Dr. Miles Payling
At the inaugural C the Signs Conference, Dr Miles Payling - Co-Founder and Chief Scientific Officer - delivered a message that captured the heart of a movement reshaping how the world detects cancer.
He spoke about science, yes. But more importantly, he spoke about people. About time. About the moments we can give back when cancer is found sooner.
“We can’t afford to wait for symptoms to become obvious. Every moment matters - because every moment lost is a choice, a treatment, a life that could have been saved.”
The question that changed everything
Miles shared the story that shaped the mission behind C the Signs.
As an NHS doctor, he met a patient named Joe - active, fit, and 60 years old. After several GP (primary care) visits with vague symptoms, Joe arrived at hospital jaundiced and unwell. Scans confirmed metastatic pancreatic cancer.
Three weeks later, Joe died.
“Joe never asked, why do I have cancer? What he asked was, why was my cancer picked up so late?”
That question became the foundation of C the Signs - a platform built to help clinicians detect cancer early enough to change the outcome.
Today, that vision makes a measurable difference: a patient with cancer detected every 22 minutes.
Each one represents a life identified sooner - and a future that’s less defined by fear.
Why early detection still falls short
Cancer remains one of the leading causes of death worldwide. Survival still depends heavily on the stage at diagnosis.
- Breast cancer five-year survival falls from 97.9% at stage 1 to 26.2% at stage 4.
- Bowel cancer falls from 91.7% to 10.3%.
- Yet only around 58% of patients are diagnosed at an early stage.
In primary care - where most people first seek help - clinicians face enormous pressures:
brief consultations, complex presentations, thousands of patients, and on average only a handful of cancer diagnoses each year. As Miles said in his conference speech:
“The problem isn’t people. It’s knowledge. We need to give every GP the power of precision - instantly.”
Early detection doesn’t fail because clinicians aren’t trying.It fails because cancer is complex, symptoms are subtle, and the time to make sense of them is short. Our platform exists to bridge that gap - offering clinicians timely clarity when decisions need to be made.
Innovation and redefining what’s possible
C the Signs brings together trusted medical evidence, real-time data and AI-powered insight to support clinicians in moments where clarity matters most.
Within seconds, our platform can highlight when a patient may be at risk and guide their doctor toward the right diagnostic pathway - across more than 100 cancer types. But the impact isn’t defined by speed, it’s defined by the lives reached sooner.
Real-world evaluations across the NHS have shown that clinicians using C the Signs are able to:
- identify patients whose symptoms signal concern - even when the signs are hard to spot
- offer reassurance by safely ruling out risk when symptoms are more likely to be benign
- give clinicians clearer insight into where a tumour may have started
- help reduce emergency cancer presentations by half
- shorten the time it takes for patients to reach a diagnosis
Each of these outcomes represents something deeply human: a patient receiving answers earlier,
a family spared uncertainty, a healthcare system given space to care, not catch up.
This is what innovation should do - not stand in the place of clinical judgement, but enhance it. It should deepen insight and make the subtle more visible, so clinicians can act early with the confidence their patients deserve.
The movement, and honouring Jess’s Rule
Miles closed by sharing the story of Jessica Brady - a 27-year-old whose symptoms were subtle, persistent and easy to misinterpret. Despite several visits to her doctor, her cancer was found too late. Her loss is felt deeply, not only by those who loved her, but by clinicians across the country who want every patient to be seen in time.
To honour her legacy, our team is introducing Jess’s Rule - a safeguard within the platform that gently alerts clinicians when a patient returns multiple times with unresolved symptoms, prompting a thoughtful, timely cancer risk assessment.
It’s a small change with a profound purpose: to make sure no patient is ever unintentionally overlooked, and no pattern is missed simply because symptoms are subtle.
As Miles said:
“We can turn tragedy into transformation - by ensuring that no patient is ever overlooked again.”
Jess’s story is a reminder of why this movement matters. Together, we can help make early cancer detection a standard for everyone - not a privilege for a few - and give each person the time, choice and hope they deserve.