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THC, cannabis and cancer
What is THC
THC, or tetrahydrocannabinol, is the primary psychoactive compound in the cannabis plant. It is responsible for the euphoric effects often associated with marijuana use. THC binds to cannabinoid receptors in the brain and affects various functions, including mood, memory, pain, and appetite. In addition to its psychoactive properties, THC also has medical uses, including relief of pain, nausea, and loss of appetite, making it an important component in medical cannabis [9, 10, 11].
THC interacts with our body’s own endocannabinoid system.
THC has shown promising results in some studies regarding cancer treatment [5, 7, 8, 16].
The difference between THC and CBD
Many confuse THC with CBD (Cannabidiol). Both substances are from the cannabis plant, but they have very different properties:
THC
Psychoactive, gives the “high,” has pain-relieving and appetite-stimulating properties. Additionally, there are examples of cancer-inhibiting effects [5, 7, 8, 16].
CBD
Non-psychoactive, has anti-inflammatory, pain-relieving, and anxiety-reducing properties [9, 10, 11].
Medical use of THC
Due to THC’s properties, it has the potential to be used medically to treat a range of conditions, including:
Pain perception
THC can interact with the body’s endocannabinoid system and reduce pain, which can be a significant benefit for cancer patients. THC can relieve both physical and neuropathic pain [9, 10, 11].
Nausea and vomiting
THC can help reduce nausea and vomiting caused by chemotherapy [9, 10, 11].
Appetite disorders
For patients who have lost their appetite due to cancer or treatment, THC can stimulate the appetite. For example, in cancer [9, 10, 11].
Sleep problems
THC can help regulate sleep patterns [9, 10, 11].
Improved quality of life
By reducing symptoms such as nausea, vomiting, and pain, THC can improve patients’ quality of life [9, 10, 11].
Mood
THC can affect mood and induce feelings of euphoria and relaxation [9, 10, 11].
Tumor growth inhibition
Some studies suggest that THC can inhibit the growth of certain types of cancer cells [5, 7, 8, 16].
Multiple sclerosis
THC can also relieve symptoms such as spasticity and pain [9, 10, 11].
Side effects
Compared to some traditional cancer treatments, THC generally has far fewer – or almost no – serious side effects [9, 10, 11].
Disadvantages of THC
Lack of regulation
The legislation surrounding medical cannabis varies greatly from country to country, which can make it difficult for patients to access safe and standardized products.
This was supposed to be addressed by the trial scheme in Denmark. But due to doctors’ extreme reluctance to prescribe cannabis – combined with the high financial price of medical cannabis – this has so far been a disappointing initiative [1, 4, 14].
Many patients are thus still relegated to the black market, where the quality of cannabis is difficult to control and penalties for selling and buying cannabis have been drastically tightened.
Psychoactive effects
THC can cause euphoria and other psychoactive effects, which are certainly not desirable for all patients. However, this can be partially addressed by dispensing cannabis in capsules that are used rectally.
Limited research
Although there are promising results, there is still a need for more research to fully understand THC’s potential and risks regarding cancer treatment. And this research has limited financial interest, so it is dragging on [5, 7, 8, 16].
Interaction with other medication
THC can interact with other medication, which can affect its effectiveness [9, 10, 11].
Recreational use
Recreational use of cannabis with THC is illegal in many countries, but the legislation is constantly evolving [12, 13].
Special precautions: Cannabis and heart disease
A often overlooked, but critical side effect of THC is its potential impact on the cardiovascular system. For people with existing heart disease, the use of cannabis may pose a significant risk.
Impact on pulse and heart rhythm:
- THC can cause tachycardia (rapid pulse) and palpitations shortly after ingestion. In less robust individuals, especially those with known heart rhythm disorders (arrhythmias) such as atrial fibrillation, this can potentially worsen the condition.
Strain on the heart:
- The increased heart rate strains the heart muscle. For patients with, for example, calcification in the coronary arteries or a history of blood clots in the heart, this extra strain can increase the risk of acute events.
Therefore, it is crucial that cancer patients who have or have had a heart disease exercise great caution.
Consideration of using cannabis as a supplement to cancer treatment should especially for cardiovascular patients be discussed with a qualified healthcare provider who can weigh the possible benefits against the potential cardiovascular risks for the individual.
Conclusion
THC is a complex substance with both medical and recreational uses. THC has shown potential as a complementary treatment for cancer patients.
THC has meant great gains for many cancer patients. Not least during chemotherapy, but also for terminal patients.
It is important to be aware that THC can have both desired and undesired effects, and that the legislation around THC is complex and constantly changing.
It is an unfortunate situation that many are relegated to the black market to get medication that greatly improves their lives. While others experience that THC is directly life-saving.
Specialist Tina Horsted
A special thanks to Tina Horsted, who is a pioneer in the use of medical cannabis and a great advocate for its spread [1, 2, 3, 4].
Specialist Tina Horsted makes a great and commendable effort for cancer and pain patients’ access to cannabis, both through research and by raising awareness of the issue in the press.
Medical cannabis in cancer
| Situation / Symptom | Recommended Form (Product) | Active Compound (Part of Plant) | Effect & Purpose |
|---|---|---|---|
| Appetite loss without euphoria | Oil or Capsules | CBG (Cannabigerol) | Stimulates appetite directly without the “high” or intoxication associated with THC. |
| Pain with gastrointestinal issues | Oil | CBG + CBD | Synergy that specifically reduces inflammation in the intestinal wall and reduces cramps in the digestive system. |
| Neuropathy (Supplementary) | Oil or Mouth spray | THC + CBD + CBG | CBG can enhance the neuroprotective effect and help regenerate nerve cells after chemotherapy (neuroprotection). |
| Acute nausea (e.g., right after chemo) | Dried flower (Vaporizer/Inhalation) | THC (Tetrahydrocannabinol) | Works within 5-10 minutes. Immediately suppresses the vomiting reflex via the lungs. |
| Prevention of nausea (Long-term) | Capsules or Oil (Oral intake) | THC | Slow absorption (30-90 min.), but long duration of effect (6-8 hours). Keeps nausea at bay throughout the day. |
| Lack of appetite / Weight loss | Oil or Capsules | THC | Stimulates the appetite center in the brain (“The munchies”). Often taken before meals. |
| Nerve pain (Neuropathy from chemo/radiation) | Oil or Mouth spray | THC + CBD (Often 1:1 ratio) | The synergy between the compounds alters pain perception. CBD dampens nerve signals, THC provides pain relief. |
| Pain with muscle tension | Oil | CBD (High content) + A little THC | CBD acts as a muscle relaxant and anti-inflammatory without causing heavy drowsiness. |
| Sleep issues (Falling asleep) | Oil (Taken 1 hour before bedtime) | THC (Dominant) | THC has a sedative effect and helps the body settle down. |
| Anxiety and restlessness | Oil | CBD (Cannabidiol – pure) | Dampens anxiety and stress response without causing euphoria. Often requires high doses. |
| Cancer fatigue (Severe fatigue) | None / Caution | CBD (Sativa strains) | Warning: THC can worsen fatigue. Pure CBD can have a mild stimulating effect in certain doses but should be used with caution. |
Overview of medicinal mushrooms and cannabis
This overview compares the effect and safety of the most used medicinal mushrooms. Cannabis is also included in the overview, despite biologically being a plant and not a mushroom. But it is often used in the same context when natural symptom relief is desired for cancer patients.
Worth knowing:
- Choice of mushroom: If the goal is to get through chemo safely with the fewest side effects, Turkey Tail is often the first choice, as it has the fewest contraindications.
- Neuropathy: If chemo causes numb fingers or nerve damage, Lion’s Mane is the only mushroom with specific documentation for being able to help with nerve regeneration.
- Stop before surgery: A good rule of thumb is to stop all mushrooms, especially Reishi, Chaga, and Cordyceps, as well as fish oil two weeks before planned surgeries due to the risk of bleeding.
Medicinal mushroom and Cannabis
| Name | Primary Effect | Use in Cancer | Name | Important Caution |
|---|---|---|---|---|
| Agaricus blazei | Very powerful immune activation. High content of Beta-1,3/1,6-glucans. | Aggressive support. Used to significantly boost NK-cell activity. | Agaricus blazei | May affect liver enzymes. Should be used with caution in liver disease or heavy liver-taxing chemo. |
| Cannabis: CBD | Anxiolytic and muscle relaxant. Anti-inflammatory. | Quality of life. Relieves restlessness, anxiety, muscle tension, and sleep problems without a high. | Cannabis: CBD | Interaction with medication. Can inhibit the liver’s breakdown of chemotherapy (CYP450). |
| Cannabigerol (CBG) | Neuroprotective and appetite stimulant. Blocks TRPM8 channels (growth signals) in cells. | Antitumour support. Targeted use for growth in colon and brain, and against loss of weight and muscle mass. | Cannabigerol (CBG) | Interaction with liver enzymes (CYP450). May affect the concentration of blood thinners and certain types of epilepsy medication. |
| Cannabis: THC | Antiemetic and appetite stimulant. Psychoactive (euphoric). | Acute relief. Against severe nausea, vomiting, and weight loss. | Cannabis: THC | Driving ban. Psychoactive side effects. Sedative effect. |
| Chaga | Powerful antioxidant (SOD). Contains Betulin and Betulinic acid. Protects against oxidative stress. | Restorative. Used for general strengthening of the body under pressure. | Chaga | High oxalate content (risk of kidney stones). Blood-thinning. Interacts with insulin (lowers blood sugar). |
| Cordyceps | Energizing. Increases oxygen uptake (ATP) and kidney function. | Lung function. Counteracts shortness of breath and cancer-related fatigue. | Cordyceps | May over-activate the immune system in autoimmune diseases. Blood-thinning. |
| Lion’s Mane | Nerve regenerating. Stimulates growth of nerve cells (NGF). | Neuropathy. Counteracts sensory disturbances in fingers/feet and memory difficulties (chemo brain). | Lion’s Mane | May lower blood sugar. Mild blood-thinning effect. |
| Maitake | Immune-activating (D-fraction). Strong stimulation of macrophages. | Immune boost. Often used to activate the body’s own defense against cancer cells. | Maitake | May lower blood sugar. Can enhance the effect of blood-thinning medication. |
| Pau D’Arco | Potent antifungal and anti-inflammatory. Contains Lapachol. | Micro-environment. Used to purify the blood and combat fungal infections (Candida), which are often seen with a weakened immune system. | Pau D’Arco | Blood-thinning. Must not be combined with blood-thinning medication or used prior to surgical procedures. |
| Pao Pereira | Inhibits replication of abnormal cells. Penetrates the blood-brain barrier. | Targeted cell division. Often used for prostate cancer and cancers of the central nervous system (brain). | Pao Pereira | Generally well-tolerated, but should be taken under guidance to ensure correct dosage relative to conventional treatment. |
| Poria cocos | Diuretic and calming. Supports spleen and kidney function. Contains Pachyman. | Fluid retention. Helps against edema and mucus. Calms restlessness and racing thoughts. | Poria cocos | Acts as a diuretic. Be mindful of electrolyte balance if taking other diuretic medication. |
| Reishi | Calming and immune-strengthening. Acts as an adaptogen (stress-reducing) and sleep-promoting. | Sleep and stress. Good for finding peace in the body and supporting the immune system between treatments. | Reishi | Blood-thinning. Must not be used with low platelets or before surgery. |
| Shiitake | Immune-stimulating. Source of Lentinan and AHCC. | Standard support. Lentinan is used medically to prolong survival in certain types of cancer. | Shiitake | May in rare cases cause skin rash (Shiitake dermatitis). Contains purines (caution in gout). |
| Turkey Tail | Immune-modulating. Supports the immune system (NK cells) without overstimulating. Contains PSK. | Chemo support. Often used alongside chemo to counteract immune suppression. | Turkey Tail | Generally considered safe. Few known interactions (approved drug in Japan as PSK). |
Back to Supplements
Also see Meta-analysis: Cannabis in cancer
Also see Rick Simpson Oil (RSO) Protocol (strong cannabis oil)
Links
[1] Tina Horsted (Horsted Institute, Website for healthcare provider)
- Content: Horsted Institute is a private pain clinic specializing in treatment with medical cannabis. The clinic, led by specialist Tina Horsted, treats patients with pain, cancer-related symptoms, and mental challenges. Their goal is to provide pain relief with the fewest possible side effects. (Danish Language)
[2] “Medicinsk cannabis – Livskvalitet og smertelindring med cannabismedicin” by Tina Horsted (NHT.nu – Anette’s Blog, undated)
- Content: A positive review of Tina Horsted’s book, which is described as a blend of facts and touching patient stories about improved quality of life. The reviewer highlights the book’s criticism of the healthcare system and argues that the resistance to cannabis is due to the fact that the plant cannot be patented and thus threatens the pharmaceutical industry. (Danish Language)
[3] Medicinsk Cannabis (Horsted Institute, undated)
- Content: A general introduction to medical cannabis as a treatment for pain and disease side effects. The text explains the difference between the plant itself and cannabis-based medicine (oils/capsules) and describes the effect of the primary active substances, THC and CBD, in relation to symptoms such as pain, nausea, spasms, and anxiety. (Danish Language)
[4] Smertelæge Tina Horsted og DanCann Pharma i samarbejde om ambitiøst patientprojekt (Ritzau, 2022)
- Content: Describes an observational study in collaboration between pain specialist Tina Horsted and DanCann Pharma. The project aims to collect data on the effect of medical cannabis for the treatment of painful late effects after cancer to create more knowledge and documentation in the area. (Danish Language)
[5] Hvordan virker cannabis i forhold til kræft (Tidslerne, 2021)
- Content: Refers to pages from the Danish Cancer Society and Herlev Hospital, both of which conclude that there is no scientific documentation that cannabis can cure or treat cancer. However, it is acknowledged that cannabis can relieve symptoms such as nausea, vomiting, and pain in connection with cancer treatment. (Danish Language)
[6] Nyt dansk studie blåstempler behandling med cannabisbaseret medicin (Dagens Medicin, 2022)
- Content: No article with this specific title could be found, and therefore no summary of the content can be provided. (Danish Language)
[7] 20 forsøg der påviser Cannabis som kur mod cancer (Cannabis Fakta.dk, 2016)
- Content: Search results refer to a large Danish study among patients about their experiences with medical cannabis. The study points to deficiencies in the current trial scheme and calls for more systematic data collection on effects and side effects, but it does not prove cannabis as a cure for cancer. (Danish Language)
[8] Medicinsk cannabis kan få disse kræftceller til at selvdestruere (Illustreret Videnskab, 2024)
- Content: The search result is a document from the Danish Health Authority about medical use of cannabis. The document describes the active substances in cannabis, but also harmful effects, including that smoking cannabis increases the risk of cancer in the respiratory tract. It does not confirm that medical cannabis causes cancer cells to self-destruct. (Danish Language)
[9] Cannabinoids: Therapeutic Use in Clinical Practice (PubMed, 2022)
- Content: Summary of scientific articles describing how cannabinoids have been shown to have a pain-relieving and anti-inflammatory effect. They can be effective against nausea caused by chemotherapy and can relieve muscle spasms and pain in patients with multiple sclerosis.
[10] Therapeutic Potential of Cannabis (PubMed, 2022)
- Content: A scientific review article that reviews the therapeutic potential of cannabis. It describes how cannabinoids such as THC and CBD are being investigated for their potential to manage a range of conditions, including chronic pain, inflammation, cancer-related symptoms, and neurological disorders.
[11] Cannabis og kræft (Kræftens Bekæmpelse, 2021)
- Content: The Danish Cancer Society acknowledges that cannabis can relieve certain symptoms and side effects of cancer disease, such as pain and nausea. However, they emphasize that there is no scientific documentation that cannabis can cure cancer. They encourage talking to your doctor if you are considering using alternative treatment. (Danish Language)
[12] Jeg er blevet min egen læge på et illegalt marked (Information, 2013)
- Content: An article highlighting how patients who experience that medical cannabis has a relieving effect can feel pressured to buy products on the illegal market if they cannot access it through the established healthcare system. (Danish Language)
[13] Afdeling på sygehus indfører cannabis-olie til kræftpatienter (DR, 2016)
- Content: Describes how a private hospital in Aarhus (Aros Privathospital) has begun to offer treatment with medical cannabis oil to their terminally ill cancer patients. The purpose is to relieve symptoms such as pain and nausea, not to cure the cancer disease. (Danish Language)
[14] Medicinsk Cannabis (Lægemiddelstyrelsen, 2022)
- Content: A page from the Danish Medicines Agency that answers a number of questions about medical cannabis in Denmark. It makes it clear that medical cannabis is only legal when prescribed by a doctor and dispensed at a pharmacy. The page also describes the rules for subsidies. (Danish Language)
[15] Søs Egelind: “Effekten ikke til at diskutere” (Sundhedspolitisk Tidsskrift, 2018)
- Content: Søs Egelind serves as a link between politicians, agriculture, and research in Cannabis Denmark and shares her personal positive experience with medical cannabis during cancer treatment, to gain political focus and develop Danish quality cannabis. (Danish Language)
[16] Therapeutic Use of Cannabis and Cannabinoids: A Review (PubMed, 2026)
- Content: A review of the therapeutic use of cannabis and cannabinoids, highlighting their medical potential and current areas of application.
[17] Nicotine and Cannabis Use in Adolescent and Young Adult Cancer Survivors: A Scoping Review (PubMed, 2025)
- Content: An overview of nicotine and cannabis use among young cancer survivors, focusing on the scope and significance for this specific group.
Page created: July 28, 2024, Last revised May 5, 2026
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