People with breast cancer may use marijuana, also called cannabis, to manage symptoms and counteract treatment side effects. Some studies suggest various benefits of cannabis for breast cancer. However, no conclusive scientific evidence has shown that it can treat cancer or manage symptoms.

Using cannabis for breast cancer is relatively common. A 2021 study that surveyed 612 participants found that 42% with a breast cancer diagnosis in the last 5 years had tried it.

People who use cannabis often report that it eases symptoms as well as side effects from chemotherapy and radiation treatments. And while some also hoped that it would improve treatment outcomes, there was no evidence supporting this.

Cannabis, like all drugs, poses some dangers, including the risk that it will interact with chemotherapy drugs or increase the risk of cancer. Therefore, people considering using it for breast cancer should consult a doctor who is knowledgeable about medicinal cannabis.

Read more to learn about how cannabis can help individuals with breast cancer, its potential benefits, risks, and more.

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Anecdotally, people who use cannabis for breast cancer cite a number of benefits. However, research supporting these claims is mostly inconclusive.

The previously mentioned 2021 study that found of those who use cannabis, the most common reason for doing so included relieving:

  • pain
  • insomnia
  • anxiety
  • stress
  • vomiting and nausea

Additionally, 49% of respondents believed cannabis could help treat cancer.

However, it is important to note there is no evidence that cannabis can help treat breast cancer. Additionally, while it is important that people discuss this with a doctor, just 39% of cannabis users with the disease did this.

A small number of studies suggest cannabis or cannabidiol (CBD) may ease nausea, nerve pain, and some other cancer or chemotherapy symptoms. Some other studies on animals suggest that the drug may reduce the need for pain medication in people with cancer.

Some evidence suggests that cannabis may help slow the growth of certain kinds of breast cancer. However, it is important to note that the data supporting this potential benefit is inconclusive.

For example, a 2020 paper reports that prior research suggests cannabinoids can slow or stop the growth of estrogen receptor-positive breast cancer. However, no clinical trials have explored the efficacy of cannabis or other cannabinoids to treat breast cancer in humans.

A 2022 study investigated the theory that tetrahydrocannabinol — the substance that causes the “high” that many people associate with CBD use — may slow tumor growth. However, in a lab setting — not a human body — researchers found that cannabis ingredients could reduce the anticancer effects of tamoxifen, a common breast cancer drug. This means that cannabis may actually undermine treatments for the disease, emphasizing how important it is to consult a doctor before using the drug.

The Food and Drug Administration (FDA) has approved two cannabis-based drugs to treat cancer symptoms but not to cure the disease itself. They include nabilone, an oral drug that can treat vomiting and nausea, and dronabinol, an oral drug that can treat vomiting and appetite loss.

Researchers do not fully understand how cannabis works or why it may help relieve breast cancer symptoms.

The body’s endocannabinoid system, which processes chemicals similar to some in cannabis, plays an important role in many functions. Chemicals in cannabis interact with the endocannabinoid system, potentially changing how the body responds to various conditions.

Studies of cannabis and its main components suggest that it may slow or reverse the growth of certain cancer cells. How it does this depends on the type of cancer cell and the type of cannabis.

For example, a 2019 study found that Cannabis sativa L. from South Africa was the most effective of the strands researchers tested for disrupting MCF-7 breast cancer cell growth. MCF-7 breast cancer is a type of hormone-positive breast cancer. However, this was in a lab setting, not a human body. Most research on cannabis’s potential role in slowing breast cancer growth has looked at hormone-positive cancers.

People who use medical cannabis should contact a doctor first. This is because the drug may disrupt the effects of certain antitumor drugs, such as tamoxifen. Therefore, taking it without consulting a healthcare professional can be dangerous.

Those considering using cannabis can lower their risk by starting with one of the approved cannabis-based drugs, nabilone or dronabinol. Additionally, cannabis may be safer, more accessible, and available at a more predictable dose in areas where it is legal.

There is no standard dose for medical cannabis beyond the FDA-approved drugs. Instead, a person should consider starting with a very low dose, observing how their body responds, and gradually increasing it as necessary.

All drugs pose risks, even if they are natural.

For example, a 2022 study suggested that cannabis use may correlate with breast cancer rates. Researchers looked at breast cancer rates in areas with liberal cannabis laws compared with those with less liberal policies. They found there were higher overall rates of the disease in the former areas.

This suggests but does not prove that increased access to cannabis could elevate breast cancer rates. Researchers do not know why this might be or if some other factor might explain this phenomenon.

Some other potential risks include:

  • Negative side effects: All drugs can cause side effects. People may feel dizzy or light-headed. They may also feel high, which can be unpleasant for some. Some individuals can also develop other, more intense side effects, including allergic reactions.
  • Mental health effects: Research points to a link between depression and cannabis use. There are also links to mania or psychosis, especially in people who have a high risk of these symptoms or have experienced them before.
  • Drug interactions: Cannabis may interact with various drugs or supplements, changing the way they work and increasing the risk of negative side effects.
  • Cancer treatment interactions: Cannabis may reduce the strength of some cancer treatments, especially those targeting hormone receptors in breast cancer.

In 19 states and the District of Columbia, there are laws regulating cannabis for nonmedical use. Most states in the United States allow cannabis for medical use, but whether a person can use the drug for cancer varies.

Getting a cannabis prescription requires a knowledgeable doctor who supports cannabis use, and it is safer to use cannabis when a person has a prescription. In states with medical cannabis laws, regulations may control cannabis dosing, making it more consistent.

Even so, access to cannabis is uneven, and factors, such as health insurance and finances, may determine whether a person can use medical forms of the drug.

Cannabis for breast cancer has shown promising results in scientific studies. Many people with the disease already use it to alleviate their symptoms and treatment side effects.

However, for most symptoms, it remains an experimental or an alternative treatment, not a medically proven one.

People who wish to use cannabis for breast cancer should understand the potential risks and benefits and consult a doctor before trying it. It is also important to note that cannabis is not a viable or effective substitute for standard cancer therapies.