Medical cannabis, also called medical marijuana, doesn’t cure any kind of cancer. But it may have benefits when you’re in treatment for breast cancer. It could bring relief for some painful symptoms of breast cancer itself, as well as some unpleasant side effects of your treatment.
It’s important to understand that even though cannabis is plant medicine — touted for making you feel groovy — it comes with risks. When you’re living with breast cancer, take those risks seriously.
Get the Basics on Marijuana
Before we get into the research and the experts’ advice on medical marijuana, let’s make sure you understand a few key terms.
You may call it pot, grass, weed, or ganja, but your doctors will call it medical marijuana or cannabis. The terms “marijuana” and “cannabis” are often used interchangeably, but there’s a subtle difference between these two.
Cannabis. The whole group or genus of plants in the Cannabaceae family, from which marijuana comes.
Marijuana. Any cannabis plant that has flowers which contain more than 0.3% THC — the psychoactive element in the plant that can make you high. Cannabis plants with less THC than that are called hemp. Hemp can’t make you high.
Now what’s THC? The cannabis plant contains two active components:
Delta-9-tetrahydrocannabinol (THC). The main part of the cannabis plant that can make you feel high, euphoric, or blissful.
Cannabidiol (CBD). This can’t make you high, but it can relax you. It’s also known to change how the body feels pain and how it responds to the inflammation that may arise after an injury.
How You Might Benefit from Medical Cannabis
As the cannabis plant contains one component that can make you feel relaxed and another that can lessen pain, you might be thinking about how it could help with your breast cancer treatment.
Breast cancer and its treatments can sometimes come with painful symptoms and uncomfortable side effects. There’s some degree of evidence — depending on the specific symptom that’s bothering you — that cannabis can help with some of these.
Let’s take a look at what the scientific evidence says.
Nausea, vomiting, appetite
“The most evidence we have is for nausea and vomiting,” says Oliva Seecoff, MD, Director of the Supportive Oncology Program at NYU Perlmutter Cancer Center in New York City. “And it’s only a modest benefit.”
Nausea and vomiting are common side effects of chemotherapy.
In a 2024 study published in the Journal of Clinical Oncology, 147 people who were receiving chemotherapy, including 55 people with breast cancer, received standard medication for nausea and vomiting plus oral cannabis capsules or a placebo. The cannabis capsules contained 2.5 milligrams each of THC and CBD, and they were taken three times a day.
Of those who took cannabis capsules in addition to regular meds, 1 in 4 had no vomiting, retching, or need for rescue medications during the five days following chemotherapy. In the placebo group that took only standard anti-nausea meds, fewer than 1 in 12 had this response.
“It's important to note that these patients were already taking standard anti-nausea medications, so this trial does not indicate that THC could be used as a replacement for standard anti-nausea treatment,” says Neil M. Iyengar, MD, Director of Survivorship Services at Winship Cancer Institute of Emory University in Atlanta, Georgia.
Researchers haven’t examined as closely whether cannabis improves appetite among people in cancer treatment, but it might be reasonable to expect that when nausea and vomiting are under control, you may be better able to eat. It’s also well known that recreational marijuana, outside of studies of people living with cancer, boosts your appetite. Munchies anyone?
Underscoring its potential to increase your appetite, there is a prescription synthetic THC called dronabinol (Marinol, Syndros) that’s FDA-approved to treat chemo-induced nausea and vomiting as well as AIDS-related weight loss and loss of appetite.
“The problem recently is that it’s not been widely available at pharmacies, and we run into many insurance issues with it, so it’s been hard to get,” Seecoff says.
Pain
Joint pain is a common side effect of aromatase inhibitors, a treatment often given to people with hormone receptor+/HER2- breast cancer. A clinical trial that included 28 women reporting joint pain from aromatase inhibitors found that 15 weeks of treatment with CBD — the component that can change pain perception and response to inflammation — could lessen pain by an average of 2 points, or just over a 10th of a point per week.
A survey of a small group of women with breast cancer who used CBD found that they had turned to the herb for help with pain, anxiety, and insomnia. They reported the greatest benefits for insomnia first, then pain.
While CBD is known to affect pain, THC may ease pain in its own way.
“Most THC products will cause a patient to feel high,” says Iyengar, who is also Chief Medical Officer of The Bettering Company, a recreational THC brand. “This can feel calming to some patients, which can be helpful for providing pain relief.”
Insomnia
While people with breast cancer who were surveyed report sleeping better when using CBD, there isn’t much research on it. There’s more evidence showing THC is helpful for sleep.
“Many of my patients report improved sleep with THC use,” Iyengar says. “There's preliminary evidence it can improve sleep and even deep sleep, but only when used in the context of broader efforts to improve sleep hygiene.” That means going to bed at the same time every night, keeping your room cool and dark, and banishing screens from your bed.
Anxiety
Relief from anxiety is one of the top reasons people with breast cancer report reaching for cannabis, but it's hit or miss whether it makes anxiety better or worse
“THC appears to decrease anxiety significantly in some patients, while even low doses can increase anxiety in others,” Iyengar says.
What’s the Right Product and the Right Dose?
Marijuana products come in many forms, from the kind that you inhale (through smoking or vaping) to edible products and drinks.
While the fastest way to get marijuana into your system and feel its effects is by inhaling it, few doctors are on board with this method.
“With long-term use, combustible methods, such as smoking, carry the risk of scarring the airway, leading to respiratory problems,” Iyengar says.
“Noncombustible methods, such as some vaping devices, present less risk from this regard, but still use high temperatures to heat the oil, which can be detrimental to the upper airway. The vaping device may also introduce other compounds that could be toxic, such as inhaled microplastics. Contaminants in the oil can even be fatal when inhaled.”
How do I choose the right edible?
First, ask your oncologist for guidance or for a referral to a palliative care specialist who can tell you how to choose the right product.
You shouldn’t get just any edible. Edibles don’t always contain the dose that’s written on the package. What’s more, the dose may not be evenly distributed throughout the product, such as a gummy. That is, you might cut the gummy in half to lower the dose, but all the THC may be concentrated on one side.
“The most reliable approach is to use medical-grade cannabis,” Iyengar says. “When this is not available or possible, it is important to use products that provide third-party testing as evidence of reliable dosing.”
Third-party testing means that before the product is packaged and sold, an unaffiliated lab tests it to make sure that the ingredients and quantities on the label are accurate. You’ll see a seal on the package, such as SC Labs or ACS Laboratory, that shows the product’s ingredients have been verified.
What’s the right dose?
Start low and work your way up.
“Even with the tiny gummies, I tell people to start with half or even a quarter,” Seecoff says. “It could take an hour or two to take effect in your body, so I wouldn’t take a second dose within two hours of taking the first and then seeing how you feel.”
The clinical trial that showed benefits for nausea and vomiting used what Iyengar considers a pretty high dose: 2.5 milligrams of THC and CBD three times a day. He recommends patients start much lower at 1 to 2.5 milligrams just once a day and only add more if needed.
Too much marijuana can backfire. Risks include nausea and vomiting, a condition called “cannabinoid hyperemesis syndrome,” extreme anxiety, and psychosis. So, start slow.
Is There Harm in Trying It?
If you’re in active cancer treatment, talk to your doctor before adding cannabis into the mix.
Drug interactions
“While THC appears to be safe for use with chemotherapy,” Iyengar says, “more research is needed to understand the potential interactions with other types of cancer treatments such as immune therapies and molecular therapies.”
Limited research has shown that marijuana might lessen the efficacy of immunotherapy treatments for cancer, such as checkpoint inhibitors, but these studies haven’t included people with breast cancer.
“There’s some data to suggest that cannabis inhibits or changes the metabolism of tamoxifen and aromatase inhibitors, which are hormone therapies, but it’s not strong evidence,” Seecoff says, “and this drug class causes a lot of interactions, many of which we say have ‘acceptable risk,’ so it’s just something to be aware of.”
Another reason it’s so important to consult your doctor before trying marijuana, Iyengar says, is because “hormone therapies are now increasingly being combined with molecular [or targeted] therapies, and there is less data currently to understand the potential for interactions with molecular therapy.”
You should also be aware that cannabis can not only increase your anxiety on its own, but it could also have a bad interaction with any medications you may already take for anxiety or depression.
Weight gain
Finally, marijuana’s potency as an appetite stimulant can be a double-edged sword for people with breast cancer, Iyengar warns. “Weight gain and metabolic dysfunction are common problems for people with breast cancer, particularly those treated with hormone therapy. Chronic THC use may increase this risk by increasing food consumption, especially if the foods consumed have a high glycemic load.” That means high in sugar or simple carbs.
Complications of breast reconstruction
A couple of recent studies have found that women who use cannabis may have a longer, harder road to recovery from breast reconstruction than those who don’t. Active cannabis users took longer to recover, were more likely to get readmitted to the hospital, and had more postsurgery complications than those who didn’t use cannabis. If you already use cannabis and you have a breast reconstruction on the calendar, talk to your doctor about the risks and any necessary precautions you should take.
What's It Going to Feel Like?
Most THC products will make you feel high. And what that actually feels like can vary from one person to the next. Being high might make you feel calm and relaxed, but it could just as easily make you feel anxious.
The dissociative feeling could be helpful for pain, anxiety, and insomnia, but “It may be jarring or disruptive for some patients, especially if it’s your first time trying THC.” If it is your first time, or if you’re going to try a higher dose, Iyengar says, “It’s important to have a trusted caregiver present who has not consumed THC at the same time.”
However, cannabis makes you feel, you can expect to feel that way for anywhere from 4 to 24 hours — another reason to start low and go slow. Edibles take longer to hit, but stay in your system longer. On the other hand, if you smoke or vape, you’ll feel the effects very quickly, possibly in minutes, but they may wear off more quickly, too.
What's the Bottom Line?
Always discuss cannabis use with your oncologist, especially its potential for drug interactions. Make sure you trust your source. Medical grade is best. Use edibles instead of inhalation, start low and slow, and have an uncompromised caregiver present.
It’s important to check cannabis use laws where you live. Cannabis isn’t legal under U.S. federal law. States, however, have varying regulations. Cannabis is legal in some states for medical use. In some other states, it’s legal for medical and recreational use. There are other states where it’s illegal for any use.
