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Cannabis use is increasing in people with serious illnesses, including people with cancer. While cannabis can help manage symptoms and side effects related to cancer and cancer treatment, it can also have harmful effects. Like most drugs, medicines, and treatments, cannabis can 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

Mental and emotional effects

Cannabis use can affect your emotions and mental abilities. This is different from cognitive impairment due to treatment, or what some people refer to as “chemo brain” or “brain fog.” However, using cannabis during treatment might make treatment-related cognitive impairment 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, including cancer treatment that can cause similar side effects. When a person continues to use cannabis, the similar effects from other medicines and treatments may continue or they may come and go.

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 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?

• Cannabis-na?ve people, or people who have never used or rarely use cannabis, 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 and other drugs) are more likely to interact with cannabis than treatments that are local (directed at a specific part of the body, like surgery or radiation).

Surgery: 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.

Radiation therapy: Very little is known about how cannabis products may interact with radiation therapy. However, 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: 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.

Chemotherapy (chemo), targeted therapy, and hormone therapy: 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.

In situations like these, be sure you have the help and assistive devices you need to be safe at home. It’s best to avoid activities such as driving, operating machinery, and using sharp utensils or instruments.

Other medicines and treatments

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 (快猫短视频) 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

Inhaled cannabis is smoked (marijuana) or vaped. While its most active chemicals are THC (delta-9-tetrahydrocannabinol) and/or CBD (cannabidiol), it also gives off harmful substances that go to the lungs when smoked, and to people who are close by. Many of the inhaled substances in marijuana smoke are the same as those found in tobacco smoke. In addition to the side effects listed above, 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

Additionally, using cannabis during pregnancy has been linked to low birth weight in babies.

Tolerance, dependency, and addiction

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 and is not the same as 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 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 products.

Financial cost

Cannabis products purchased through licensed dispensaries and other retailers are not covered by insurance. This is because federal law still considers cannabis an illegal drug, with the exception of hemp. Here are some ways the cost of cannabis can impact people with cancer.

• 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.
• There is a risk for high out-of-pocket costs for those using cannabis to relieve symptoms related to cancer and its treatment. This adds to the overall financial burden of having cancer.
• Because they tend to use cannabis products more, men and younger people with cancer are more likely to have high 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 regulated types and forms, may be poor quality, and may contain unknown or dangerous substances. It’s also important to store cannabis safely and to keep it away from children and pets.

Ingredient safety

Some cannabis/cannabinoid products contain amounts of cannabinoids that differ substantially from what’s stated on their labels. It’s important to buy cannabis products from licensed dispensaries and sellers whose products are regulated by the FDA.

Buying products that claim to contain cannabis from people selling them on the street, the internet, or elsewhere is dangerous. These illegal substances are not regulated, could be lower quality, may contain varying amounts of cannabis, and may contain harmful ingredients. There have been reports of cannabis products being tainted or contaminated with bacteria, pesticides, and other harmful or unknown substances.

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 drink 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.