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Cannabis refers to a family of plants from which marijuana and hemp are produced. These plants are grown around the world and have been used in herbal remedies for centuries.

In modern times, marijuana has generally been viewed as a recreational drug. But there is growing interest in its medical uses. The terms “medical marijuana,” “medical cannabis,” “medical hemp,” or “medical CBD” refer to the use of products made from the cannabis plant to treat certain health conditions.

Many people diagnosed with cancer report that cannabis products are effective for managing their symptoms and treatment side effects. There is some research supporting the use of medical cannabis for managing certain conditions, but federal laws in the United States make it difficult to study medical cannabis.

It’s important to know that cannabis is not a cure or treatment for cancer itself, even though there are many such claims online. You should not use medical cannabis instead of proven cancer treatments.

What are cannabinoids?

Cannabis plants contain many chemicals known as cannabinoids. Cannabinoids cause certain effects when you consume them. They do this by interacting with your body’s endocannabinoid system, which actually produces its own cannabinoids called “endocannabinoids.” Scientists are still working to understand how the endocannabinoid system works, but it seems to play a role in many processes in your body.

The research done on cannabis so far suggests that most of its medical benefits are related to the effects of two main cannabinoids:

  • THC (delta-9-tetrahydrocannabinol), which causes the high associated with marijuana
  • CBD (cannabidiol), which does not cause a high

THC and CBD seem to offer different medical benefits. A good example of these differences can be seen when comparing the only cannabinoid medicines approved by the U.S. Food and Drug Administration (FDA): Marinol (chemical name: dronabinol) and other synthetic THC medicines are approved to treat nausea caused by chemotherapy. The CBD medicine Epidiolex is approved to treat seizure disorders in children.

Different forms of cannabis contain different amounts or combinations of cannabinoids. Marijuana contains enough THC to cause a high (more than 0.3%) and varying amounts of CBD. Hemp contains mostly CBD and only trace amounts of THC, which does not cause a high.

Cannabis products made from extracted oils can contain all or mostly THC or CBD, or different combinations. “Whole plant” marijuana products are often grouped by “strains” to describe their balance of THC and CBD. Whole plant or “full spectrum” products often contain other cannabinoids that can cause other effects.

The effects of cannabinoids also vary depending on how they are consumed. The most common ways to consume medical cannabis are:

  • eating “edibles” or taking capsules, oils, or tinctures by mouth, which can take one to a few hours to take effect and can last for up to 6 hours
  • inhaling cannabis smoke or vapor, which takes effect within minutes and fades over a few hours

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What conditions is medical cannabis used for?

It’s extremely important to know that cannabis is not a cure or treatment for breast cancer, despite many claims. It’s dangerous to use cannabis instead of proven cancer therapies. It’s also important to talk to your doctor before using cannabis products to make sure it won’t interact or interfere with any of your medicines or treatments.

People use cannabis products to manage cancer symptoms, treatment side effects, and other challenges along the cancer journey. The most common reasons people with breast cancer use cannabis are to manage:

  • pain (including joint and muscle aches, discomfort, and stiffness)
  • anxiety and stress
  • insomnia
  • nausea, vomiting, and loss of appetite caused by chemotherapy

Some studies support the use of cannabis for these conditions. Still, because marijuana is federally illegal in the United States, research on medical cannabis to manage cancer symptoms and treatment side effects is limited.

Patient surveys have provided important insights about how people use medical cannabis. About 42% of people diagnosed with breast cancer who completed our survey said they used medical cannabis products to manage breast cancer symptoms or treatment side effects. The people who used medical cannabis ranged in age, cancer stage, and treatment phase, and most (75%) found it to be “very” or “extremely” helpful.

But again, it’s important to talk to your doctor about using cannabis products, especially during cancer treatment, to make sure it’s a safe option for you. If you find that your doctor is not knowledgeable or experienced with cannabis, you may want to seek advice from an oncologist who participates in your state or country’s medical cannabis program.

“It’s important for people to know that anything they ingest that produces a change in their bodies is acting like a drug, and it has the potential for side effects, interactions with other drugs, as well as benefits,” said Virginia F. Borges, M.D., MMSc., professor of medicine and director of the Breast Cancer Research Program at the University of Colorado Cancer Center. “People have to be as diligent about researching medical marijuana as they would be with any other supplement or drug they were taking.”

Because marijuana has been legal for both medical and recreational use in Colorado for many years, Dr. Borges has cared for a number of breast cancer patients who use or have used medical cannabis to ease treatment side effects.

“I’ve mainly seen it used in conjunction with prescription drugs to control pain and other side effects in patients living with metastatic disease,” she said. “It’s rare that a person living with metastatic breast cancer would have only one side effect to manage. So, by adding in medical marijuana, it often allows me to cut back on the number of drugs I prescribe. With a high-quality source for medical marijuana and knowing how it affects an individual, using medical marijuana can put more control back in the hands of my patient.”

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Is medical cannabis legal?

The legal status of cannabis for either recreational or medical use varies across the world and continues to change. It’s important to understand the laws in your state or country before you purchase or use cannabis.

Marijuana (the form of cannabis that contains more than 0.3% THC — enough to cause a high) is illegal nationwide under federal law in the United States. At the same time, most U.S. states have passed their own laws either legalizing the use of marijuana entirely or to treat certain medical conditions. But even in states where marijuana is legal, U.S. federal government employees and people who work for companies that receive federal grant funding cannot legally use marijuana under the Drug-Free Workplace Act.

Many other countries also allow the use of medical marijuana, including Australia, Canada, the United Kingdom, and many others in Europe and South America.

Marijuana laws vary from state to state in the U.S. Some states allow people with certain health conditions to get a medical marijuana card through their doctor, which allows them to buy cannabis products at an approved dispensary. Other states only allow the medical use of CBD to treat certain serious conditions. In states where marijuana is legal for recreational use, anyone of legal age can buy cannabis products from a dispensary, but some of these shops carry medical products that are only available to people with certain health conditions.

If marijuana is legal where you live, it’s important to know that quality control of these products can be uncertain. Most cannabis products, even those sold at medical dispensaries, are not regulated like other medicines. They may contain contaminants such as mold, heavy metals, and pesticides, and the labels may include incorrect information about types, doses, and ingredients. You can ask the dispensary for a “certificate of analysis” for the products you might buy, which tells you about ingredients, dose, and contaminants.

Medical cannabis is not approved by the FDA for use in people with cancer. But three synthetic THC medicines have been approved to treat nausea and vomiting caused by chemotherapy:

  • Cesamet (chemical name: nabilone)
  • Marinol (chemical name: dronabinol)
  • Syndros (chemical name: dronabinol in liquid form)

In Canada and some European countries, Sativex (chemical name: nabiximols), an oral spray containing equal amounts of THC and CBD, is approved for the treatment of certain types of pain related to cancer.

Epidiolex, a medicine with CBD extracted from marijuana, is FDA-approved for use in children with severe seizure disorders. It is not approved for people with cancer, but studies are ongoing.

What about CBD products?

CBD products can be made from marijuana or hemp (the form of cannabis that contains only trace amounts of THC and does not cause a high). In the U.S., CBD products have typically only been available at medical marijuana dispensaries.

However, the U.S. Congress passed a federal law called the 2018 Farm Bill. This law made it legal for companies to produce and sell CBD products made from hemp. Now, many more companies are selling CBD products. You’ve probably seen them everywhere from grocery stores and pharmacies to gas stations and online ads.

But just because CBD products made from hemp are sold everywhere, in all kinds of products, and their legal restrictions have been loosened, you shouldn’t assume they are safe, effective, or even legal where you live (some state laws still consider hemp CBD illegal).

Like all cannabis products, hemp CBD products are not regulated the same way medicines are. So it’s hard to know if they are made safely, contain contaminants, or are labeled accurately. It’s also illegal for companies to market any cannabis product as a cure, treatment, or dietary supplement. The FDA has warned many companies that have marketed CBD products in this way.

Medical grade CBD products from a medical marijuana dispensary or an independent pharmacy are likely a safer and more effective option, because you can ask for a certificate of analysis that tells you about the ingredients, dose, and if there are contaminants such as mold, heavy metals, or pesticides.

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What to expect when using medical cannabis

The ways cannabis can affect you depends on many factors and can be hard to predict. The effects of cannabis can vary from person to person.

Also, cannabis comes in a variety of strains, each with different potency and amounts or combinations of cannabinoids. Of note, products that contain THC may cause a high, while products with CBD only or trace amounts of THC will not.

The way you consume cannabis can also influence the effects. Cannabis products come in many different forms, including:

  • edibles, such as cookies, candy, mints, or brownies
  • gelcaps or pills
  • dried leaves or buds for smoking, vaporizing, or making tea
  • tinctures or sprays that are used under the tongue or along the gum line
  • oils for inhaling with a vape pen or vaporizer
  • oils for mixing into tea, honey, or food
  • creams and other products that are applied to the skin

Eating edibles or taking oils by mouth can take one to a few hours to take effect and can last up to about 6 hours. It can be difficult to know the dose in some edibles and how long the effects will last. Oils, sprays, and tinctures may give you more control over the dose you take.

Inhaling cannabis smoke or vapor takes effect within minutes and fades more rapidly. Inhaling can give you more control over the dose you take, when the effects will start, and how long they will last. But many oncologists prefer that their patients not smoke or vaporize cannabis products, especially during active cancer treatment that can affect the lungs or immune system. That’s one reason why it’s important to talk to your doctor before you start using cannabis.

Every person’s situation is unique. The best forms and doses of medical cannabis and the reasons for using it will vary from person to person.

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Side effects and safety of medical cannabis

Information on cannabis side effects is limited because research on medical cannabis in people with cancer is limited. Side effects are also likely to vary depending on the dose you take and the amounts and combinations of THC and CBD in each product.

Reported side effects of marijuana, which has THC, include:

  • increased heart rate
  • low blood pressure
  • dizziness and falling
  • tiredness, fatigue, sleepiness
  • fainting
  • hallucinations
  • paranoia

CBD is usually well-tolerated, but reported side effects include:

  • drowsiness and fatigue
  • dry mouth
  • diarrhea
  • reduced appetite

It’s not well understood how cannabis products may interact with other medicines, including cancer therapies. That’s why it’s important to talk to your doctor about using medical cannabis both before and during treatment. Working together, you can come up with the best way to relieve your symptoms.

“The medicines and therapies you use can interact with each other. They may meet up and cause no effect, a beneficial effect, or a harmful effect,” said Marisa Weiss, M.D., founder and chief medical officer of Breastcancer.org and director of breast radiation oncology at Lankenau Medical Center. “For example, a helpful effect is when cannabis reduces nausea from chemotherapy. But a harmful effect can happen if cannabis interferes with the benefit of chemotherapy or increases the risk of lung damage during radiation and chemotherapy if cannabis is smoked or vaped.”

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Important things to consider before using medical cannabis

If you decide that you’re interested in trying medical cannabis to treat your breast cancer symptoms or treatment side effects, here are some things to consider before you do:

  • Talk to your doctor: As with all vitamins, supplements, herbs, and over-the counter medicines, always tell your doctor if you are using any type of cannabis product to make sure it won’t interact or interfere with your cancer treatments.
  • Find a doctor in a medical marijuana program: If you live in a place where medical marijuana is legal, make an appointment with a doctor who participates in your state or country’s medical marijuana program. These are doctors who are trained and certified to qualify patients for medical cannabis and oversee their care. Some states also certify trained nurses, physician’s assistants, and pharmacists to qualify patients for medical cannabis.
  • Find a medical cannabis dispensary you are comfortable with: Most oncologists prefer that their patients get their medical cannabis products from a medical cannabis dispensary if they are available where you live. Medical dispensaries focus on medical patients rather than just recreational users. They should have knowledgeable staff members or a pharmacist who can answer your questions about their products.

    It can be helpful to call the dispensary ahead of time to explain the issues you’re having and ask if you can schedule an appointment with a knowledgeable staff member. Ask if there is a pharmacist or doctor available at the dispensary. You should share a complete list of medications and supplements you’re taking to avoid any unsafe interaction between products. You also should let the dispensary know if you have any allergies. For example, if you’re allergic to coconut, then you should avoid the commonly used coconut oil-based products.
  • Learn about different medical cannabis products: Every medical cannabis dispensary has its own menu of products. Depending on where you live, medical cannabis dispensaries may have pharmacists on staff who can review your unique situation and make tailored recommendations.

    When choosing products, it’s important to understand the different effects of THC and CBD. THC and CBD each offer different medical benefits. For example, CBD may be better at easing anxiety, while THC may be better at controlling nausea caused by chemotherapy.

    THC and CBD are present in different levels in different strains of marijuana. Most medical cannabis products are made by extracting these cannabinoids from the cannabis plant and putting different amounts of them into the products. The label on the product usually shows the ratio of THC to CBD. Hemp products mostly contain CBD, but can have trace levels of THC and other cannabinoids which are unlikely to be listed on the label.

    It’s also important to ask questions about the safety and quality of the products you are buying. Some doctors who certify people for medical marijuana suggest asking the dispensary staff member some general questions before you start talking about your symptoms and side effects, such as:
    • Is the cannabis in your products grown with any pesticides?
    • Are your products stored and handled properly to avoid spoilage and contamination?
    • Is there a “sell by” date on the packaging?
    • Are your products tested for fungus, bacteria, or pesticide levels? What are the results? (Ask for a certificate of analysis or “COA”).
    If you’re interested in CBD, look for a medical-grade product. Many regular pharmacies sell CBD products made from hemp. Ask the pharmacist for recommendations. You can also purchase medical-quality CBD online.
  • Talk to people with breast cancer who have used medical cannabis: If you’d like to talk to someone who is successfully using medical cannabis to treat breast cancer side effects, you may want to ask your cancer care team if they can connect you with another patient.
  • Consider costs: Medical cannabis can be expensive. It is not covered by insurance, Medicare, or Medicaid in the United States. And it isn’t covered in most other countries. The cost of medical cannabis can start at about $50 per month but can be much higher depending on how much is needed. Also, getting a medical marijuana certification card is unlikely to be covered by insurance. This cost can vary from $50 to $500 depending on where you live. Medical cannabis products from dispensaries usually must be paid for in cash. Medical certification is usually not required to buy CBD products made from hemp, and a credit card can be used to pay for them.
  • Know that cannabis works differently for everyone: You will likely have to do a lot of research on your own and try various products to figure out the dose and ratio of CBD to THC that works best for controlling your symptoms and side effects. This can require some trial and error. What works for someone else may not work for you. It’s best to “start low and go slow” as you increase the amount of medical cannabis you are taking.
  • Don’t use cannabis if you have certain medical conditions: If you have had a heart attack or have a serious heart condition, you may be at higher risk of having a heart attack from using marijuana. If you have regularly used marijuana in the past and it gave you severe nausea and vomiting, then you should avoid using marijuana products. This condition is called cannabis hyperemesis syndrome and is only cured by stopping all marijuana use.
  • Think carefully about the delivery method you choose: Smoking or vaporizing cannabis or its oils may not be the safest choice for people receiving certain cancer treatments or with underlying lung conditions such as asthma, COPD, and interstitial lung disease (scar tissue in the lung caused by infection, smoking, or a variety of medications). Talk to your doctor to make sure inhaling cannabis is appropriate for you.
  • Make sure using medical cannabis won’t put your job at risk: If you are a teacher, bus driver, corrections officer, government worker, or someone who works for a company that receives federal grant funding, you may face disciplinary action or lose your job for using any form of cannabis — even CBD products, which often contain trace amounts of THC. Always check your employer’s medical cannabis policy before you start using it, especially if you are subject to regular drug tests.
  • Talk to your doctor if you are in a clinical trial: If you are part of a clinical trial, it may be unknown how cannabis can interact with any experimental medicines. It makes good sense to talk to the doctor coordinating the trial before you use marijuana or hemp products.

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Written by: Adam Leitenberger, editorial director

This content was developed with contributions from the following experts:

Donald I. Abrams, M.D., Zuckerberg San Francisco General Hospital; Osher Center for Integrative Medicine; University of California San Francisco

Virginia F. Borges, M.D., MMSc., professor of medicine and director of the Breast Cancer Research Program at the University of Colorado Cancer Center

Marisa Weiss, M.D., founder and chief medical officer of Breastcancer.org; director of breast radiation oncology at Lankenau Medical Center, Wynnewood, Pa.


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