Melatonin is a supplement known for its ability to help people sleep. Recent evidence suggests that it may also help lower the risk of breast cancer, slow tumor growth, and improve treatment outcomes.

Taking melatonin is considered safe for most people with breast cancer. However, it can interact with several prescription medications, so it’s best to ask a doctor before using it.

In this article, we take a closer look at what researchers have found about the link between melatonin and breast cancer prevention and treatment.

Recent research has looked at the possibility that melatonin might help prevent breast cancer, slow its growth, and make treatment more effective or tolerable.

Prevention

A 2018 research review suggests that the antiestrogenic (a substance that prevents cells from making and using estrogen) and antioxidant properties of melatonin might help lower the risk of breast cancer.

Researchers of a 2021 review have also found evidence from past studies indicating melatonin’s potential therapeutic use in helping to lower breast cancer risk.

Growth suppression

A 2021 study demonstrates that melatonin might help slow the growth of triple-negative breast cancer (TNBC), a fast-growing and hard-to-treat cancer.

This ex vivo (tissue) study found that melatonin may suppress a key cell signaling pathway involved in TNBC development. In other words, melatonin may help block the ability of TNBC cells to:

The findings of a 2025 research review also suggest that 3 to 20 milligrams per day of melatonin may help suppress tumor growth and breast cancer metastasis.

In another recent study, researchers concluded that melatonin may be a promising anticancer agent — and not just for breast cancer.

Treatment

While more research on using melatonin to help treat, or even cure, cancer is needed, a 2021 research review citing older studies indicates that it may help improve the therapeutic efficacy of cancer treatment, such as chemotherapy.

Other recent studies suggest that melatonin may help with chemo-induced side effects, including fatigue, and improve quality of life while undergoing treatment for breast cancer.

More research is needed

Research is still ongoing. There’s not a clear answer on the effectiveness of melatonin in treating and preventing breast cancer.

Data shows that melatonin can likely help prevent and slow the growth of breast cancer, but there isn’t enough information yet to show a clear link. There are no official recommendations about melatonin from any major health agencies.

Melatonin is safe for most people during breast cancer treatment. However, it can interact with some medications, so it’s a good idea to talk with your doctor before you begin taking it.

There are no noted interactions with chemo drugs. But if you are taking medications for other conditions while receiving treatment for breast cancer, melatonin could be unsafe.

Possible interactions include certain medications for:

The long-term use of melatonin hasn’t been fully studied. Melatonin may alter hormone levels if it’s taken long-term. This could have risks and negative side effects for some people.

Your doctor or oncologist can provide more information about the safety of melatonin use while living with breast cancer.

Melatonin is most known for its use as a sleep aid. Anecdotal evidence and early research suggest that it might also affect mental and physical health.

Known effects of melatonin for people with breast cancer include:

Some people undergoing breast cancer treatments, such as chemo, find that melatonin helps them relax and sleep. It might also help lower stress levels and help with depression, anxiety, and other mood conditions.

Keep in mind that these uses of melatonin aren’t backed by research and data.

However, as long as you’re not taking any medications known to negatively interact with melatonin, it’s generally safe to take during breast cancer treatment. Still, speak with your doctor to be sure.

Pros of using melatonin for breast cancer

  • may help with prevention
  • may help slow tumor growth and metastasization
  • may help improve treatment efficacy and treatment side effects

Cons of using melatonin for breast cancer

  • may interact with medications for other health conditions
  • not studied for long-term use
  • may increase risk of sleepiness, dizziness, and nausea

It can be hard to eat a standard diet during treatment, and you might not be getting the nutrients your body needs.

Some people find that taking supplements during breast cancer treatment helps them feel better by boosting their body’s energy and health.

Be sure to talk with your doctor first

It’s always best to talk with a doctor before you begin any supplements. This is particularly true if you’re undergoing treatment for breast cancer.

Supplements that are typically safe to take if you have breast cancer

The following supplements are generally considered safe and helpful to take if you have breast cancer:

Supplements to avoid if you have breast cancer

Some supplements might be dangerous to take during chemo and other breast cancer treatments:

Common dietary products and aids such as green tea, probiotics, and grapefruit juice have been linked to some negative effects for people undergoing chemo.

The above lists may not be all-inclusive. Determining which supplements are and are not safe depends on the treatment you’re undergoing. Be sure to talk with the doctor who’s treating your cancer about supplements they recommend or supplements you’re considering taking.

No, melatonin hasn’t been shown to lower estrogen levels. Though research does suggest it can modulate estrogen responsiveness.

Some studies have focused on the link between melatonin and specific types of breast cancer, such as triple-negative breast cancer.

However, most research has looked at the possibility that melatonin could decrease the spread of all breast cancer cells.

Although more data is needed, evidence points to melatonin being a potential option for all types of breast cancer.

There’s not enough evidence to say if melatonin can prevent breast cancer recurrence. Melatonin may help lower your overall risk of recurrence, but there isn’t enough data to prove this.

Research from 2025 performed in rats suggests that melatonin may help reduce the growth of glioblastoma tumors.

A 2021 study examined the effect of melatonin on breast and prostate cancer. The researchers found that melatonin might help slow the growth of both cancers.

Recent research suggests that melatonin may have potential use in lowering the risk of breast cancer, slowing the growth of breast cancer, and helping to make breast cancer treatments more effective or tolerable.

Still, further study is needed, but current data is promising.

Melatonin use is generally considered safe for most people with breast cancer. It can interact with some medications, though, so it’s best to talk with a doctor before taking melatonin.