Risks of Using Cannabis for People With Cancer
Cannabis use is increasing in people with cancer to help manage symptoms and side effects related to cancer and cancer treatment. Like most drugs, medicines, and treatments, cannabis can also cause side effects and complications. There are also concerns about cost and safety, as well as legal issues.
If you or a loved one are interested in trying cannabis to help manage symptoms of cancer or side effects of treatment, it’s important to learn as much as you can about it. Talking with your doctor or cancer care team about the types, forms, doses, risks, and benefits can help you make an informed decision, address any safety issues, and know what to expect.
Immediate effects of cannabis use
Cannabis use causes changes in mood, thinking, and balance that can cause safety concerns. The effects depend on the type and amount used.
Mental and emotional effects
Cannabis use can affect your emotions and mental abilities. Using cannabis during treatment might make treatment-related cognitive impairment (also called chemo brain or brain fog) worse for a short time, or cause different mental or emotional effects.
When mental and emotional effects of cannabis take effect and how long they last depends on the type, form, and dose of cannabis used. Some of the possible mental and emotional effects of using cannabis are:
- Feeling of being “high”
- Confusion
- Drowsiness or feeling sleepy
- Mood changes
- Feeling paranoid
- Memory problems
- Problems focusing or concentrating
- Risk-taking or poor judgment
- Hallucinations
Keep in mind the memory, thinking, and focus changes that can happen when cannabis is used typically go away after a dose of cannabis wears off. However, people with cancer are often taking other medicines that can cause similar side effects. Using cannabis along with other medicines that affect thinking, mood, and focus is a safety concern because doing so can worsen these side effects.
Physical effects
Some side effects of cannabis might lower your ability to take part in physical activities and may limit how you’re able to do your usual daily activities and self-care. If you’re already having similar physical effects from cancer and its treatment, adding the effects of cannabis can be a mobility or safety concern.
When physical effects of cannabis take effect and how long they last depends on the type, form, and dose of cannabis used. Some of the general physical side effects of using cannabis are:
- Dizziness, feeling lightheaded, or fainting
- Fatigue
- Feeling clumsy, off-balance, or uncoordinated
- Dry mouth
Safety concerns
The mental, emotional, and physical effects of using cannabis products can lead to unsafe situations. It’s important for people using cannabis and their caregivers to be aware of how its use might impair their mental and physical abilities and to take steps to keep themselves protected from injury.
- Be aware you might feel dizzy or lose your balance, raising your risk of falls, injuries, and other accidents.
- Driving a vehicle after inhaling or ingesting cannabis is not legal and can lead to impaired and unsafe driving. In fact, driving while under the influence of cannabis can almost double your risk of having a motor vehicle accident.
- There are additional safety concerns for people who have certain jobs that involve heavy equipment and hazardous materials. Do not operate heavy equipment or work with hazardous materials while using cannabis.
Who is at highest risk?
- People who are cannabis na?ve have never used cannabis. These people, and those who rarely use it, can be at risk for greater side effects than people who have used cannabis for longer periods of time.
- People who have a history of a substance use disorder have a higher risk of misusing cannabis.
- Cannabis use may worsen psychotic disorders, such as schizophrenia.
- People taking medicines known to have interactions with cannabis should be closely monitored.
Interactions with medicines and treatments
Like any drug or treatment, cannabis can interact with other medicines. Cannabis can cause changes in how the other drug works in the body, and it may make side effects worse.
It’s very important to be sure your cancer care team knows all of the drugs, medicines, supplements, and treatments you are taking so they can be alerted to possible interactions, help you manage side effects, and address any safety concerns.
Cancer treatments
There is very limited research on how cannabis may interact with cancer treatments. Treatments that are systemic (that travel through the body, like chemo, targeted therapy, and immunotherapy) are more likely to interact with cannabis than treatments that are local (directed at a specific part of the body, like surgery or radiation).
Cannabis users may be at higher risk for problems with anesthesia and other complications during and after surgery. If you use cannabis and are having surgery, be sure your surgeon and anesthesia specialist know about the type, form, and dose of cannabis you use and how often you use it.
Very little is known about how cannabis products may interact with radiation therapy. The few studies available have not shown that using cannabis while getting radiation therapy causes harm. In fact, there is some evidence that cannabis can be used to help reduce anxiety and side effects related to radiation treatment, such as pain and nausea.
Immunotherapy uses a person's own immune system to fight cancer. It can boost or change how the immune system works so it can find and attack cancer cells. Some studies suggest that using cannabis while on immunotherapy medicines or treatments can lead to the immunotherapy not being as effective. If you are using cannabis or thinking about using it, and your treatment plan includes immunotherapy, talk with your doctor about possible interactions.
Cannabis has been studied to help control side effects from these treatments, but the direct interaction of cannabis with chemo, targeted therapy, and hormone therapy has not been studied much. Because of this, your doctor likely won’t be able to give much information about how cannabis might interact with these treatments.
Symptom management medicines
Many people with cancer take medicines to manage symptoms of cancer and side effects of treatment. In some cases, using cannabis along with these medicines might affect how the medicines work. Keep in mind the effects of cannabis typically go away after a dose of cannabis wears off. However, when a person continues to use cannabis, the combined effects may continue or may come and go. For example:
- Sleep and pain medicines can cause you to feel tired or sleepy like some cannabis products. If both are used, these side effects can be enhanced.
- If you have cancer-related fatigue, cannabis may cause you to feel more tired and weak. This can lead to a higher risk of losing your balance or falling and getting injured.
Be sure you have the help and any assistive devices you need to be safe at home. It’s best to avoid activities such as driving, operating machinery, and using sharp objects.
Other medicines and treatments
Certain prescription medicines can interact with cannabis. The medicines with the highest risk for interaction with a cannabis product include:
- Warfarin (Coumadin, Jantoven): an anticoagulant to help prevent blood clots
- Buprenorphine (Sublocade, Brixadi, Subutex, Butrans): an opioid pain medicine
- Tacrolimus (Astagraf, Envarsus, Prograf): a transplant anti-rejection medicine
Alcohol
Studies have shown that when cannabis is used with alcohol, there’s an increased risk of being impaired, both mentally and physically.
The American Cancer Society (大象tv) Guideline for Diet and Physical Activity for Cancer Prevention and Nutrition and Physical Activity Guideline for Cancer Survivors recommend that it’s best not to drink alcohol.
Long-term health risks of cannabis
Cannabis is known to increase the risk of multiple health conditions with frequent use over many years.
Recent studies have looked at whether adults using cannabis for long periods of time have an increased risk for certain types of cancer. The studies have shown a link between cannabis use disorder and the development of head and neck cancers. However, more research is needed to fully understand this link, as well as other cancer-related risks of using cannabis.
Inhaled cannabis (marijuana) is smoked or vaped. When inhaled, harmful substances go into your lungs and those of people who are close by. Many of the inhaled substances in marijuana smoke are the same as those found in tobacco smoke. In addition, smoking cannabis can cause heart and lung problems, including:
- A cough that may last months to years
- Decreased lung function, which can be seen on pulmonary function tests (PFTs)
- Increased heart rate
- Increased risk of having a stroke or heart attack
Using a lot of cannabis regularly (more than weekly) over many years may cause mild problems with memory, thinking, and paying attention. But these problems usually go away after a person stops using cannabis. Researchers still need to fully study how long-term cannabis use affects the brain.
Even though cannabis is often used to help with nausea, long-term, regular use can actually cause cannabis hyperemesis syndrome, or CHS. Hyperemesis means severe nausea and vomiting. CHS is a condition some long-time regular cannabis users might have. It’s usually seen in those who have used cannabis for 10-12 years or more.
Symptoms of CHS include:
- Ongoing or frequent bouts of nausea
- Repeated and frequent vomiting
- Loss of appetite
- Abdominal (belly) pain
Symptoms of CHS typically resolve when cannabis use is stopped for several days or weeks. Symptoms may resolve completely but may return if cannabis is used again.
Not all long-time cannabis users develop CHS and it is not known what causes it. It’s hard to know exactly how common CHS is since not all cannabis users report their cannabis use to doctors or seek medical help when CHS occurs. However, research indicates that CHS is becoming more common.
A person’s body can get used to taking certain drugs, medicines, and treatments. When this happens, sometimes the drug, medicine, or treatment doesn’t have the same effect as it did when the person started taking it. This is called developing tolerance. Tolerance can lead to dependency or addiction.
- Tolerance is when your body gets used to a certain dose of a drug or medicine, and you might need a higher dose to keep getting relief.
- Dependency is when your body has developed a tolerance for a drug or medicine and needs that drug or medicine to function well. If you stop using the drug or medicine, withdrawal symptoms can happen.
- Addiction (sometimes called substance use disorder) is not the same as dependency. Addiction is when you have a strong urge or craving for using a drug, the urge is very hard to control, and there are harmful behaviors and effects in your life because of using the drug.
Over time, some people who use cannabis might become dependent on it. For example, a person using cannabis might not seem to get as much relief after taking it for a while. Sometimes this is because the symptom or side effect has increased, or they have developed a tolerance to cannabis. When this happens, a different form or dose might help to get the relief that’s needed.
Studies show that some chronic users can develop an unhealthy dependence on cannabis. This is called cannabis use disorder (CUD). According to the Centers for Disease Control and Prevention (CDC), CUD affects about 3 in 10 people who use cannabis.
Using cannabis during pregnancy has been linked to low birth weight in babies, pre-term birth, and an increased risk of stillbirth. No amount of cannabis use is considered safe during pregnancy.
Cannabis products purchased through licensed dispensaries and other retailers are not covered by insurance. This is likely because federal law still considers cannabis an illegal drug, with the exception of hemp. But the cost of cannabis can add to the overall financial challenges many people with cancer experience in different ways.
- The cost and taxes related to buying cannabis for medical reasons vary in each state where it is legalized. Costs also vary based on prices set by the dispensary selling it and by the type, dose, and form of cannabis being sold.
- Because they tend to use cannabis products more, men and younger people with cancer are more likely to have higher out-of-pocket cannabis costs.
- Little is known about the value of various types of cannabis products based on how much they cost.
Insurance may or may not cover the 2 prescription cannabinoid medicines that require a doctor’s prescription, dronabinol and nabilone. They are available at most pharmacies, even in states where medical cannabis is illegal. If your doctor recommends one of these, be sure to check with your insurance company to see if it’s covered and how much out-of-pocket cost you may have.
Product safety
Where and how cannabis is purchased is important. Keep in mind that cannabis products that people get or buy from sellers on the street or vendors on the internet may not be safe. They may not be regulated, may be poor quality, and may contain unknown or dangerous substances. There have been reports of cannabis products being tainted or contaminated with bacteria, pesticides, and other harmful or unknown substances.
It’s important to buy cannabis products from licensed dispensaries and sellers whose products are regulated by the US Food and Drug Administration (FDA).
Storage of cannabis
Store cannabis products in a clean, dry, cool area or as directed on the label. The area should be away from where food and drinks are stored. Cannabis products should also be stored and kept out of reach of children, pets, and others at risk for accidental cannabis dosing. Using a locked cabinet is a good idea.
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- References
Developed by the American Cancer Society medical and editorial content team with medical review and contribution by the American Society of Clinical Oncology (ASCO).
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Last Revised: July 11, 2025
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