Phytotherapy & cancer: is natural always safe?

Many people with cancer look for ways to feel better during or after treatment. Some turn to plant-based products, such as herbal teas or essential oils. This approach is called phytotherapy. You will find countless of plant-based products in a pharmacy or online. But can these preparations safely support people during or after treatment? Or do they have hidden risks?

What is phytotherapy?

Phytotherapy is the use of plants, or preparations made from plants, with the aim of helping to prevent, relieve, or treat a disease or symptom. It is classified as part of complementary and alternative medicine.

Phytotherapy is not the same as homeopathy. Homeopathy is based on extreme dilutions, often leaving little or none of the original substance in the final product. See our blog on homeopathy for more information. Phytotherapy, in contrast, uses plants that contain biologically active substances. These substances can have real effects in the body.

Different forms, different concentrations

Plant-based preparations can come in different forms, such as:

• herbal teas
• essential oils, used for example in aromatherapy
• plant powders
• liquid extracts
• dry extracts

These forms are not interchangeable. An essential oil, for example, is much more concentrated than a herbal tea. A dry extract may also contain a much higher concentration of active plant substances than the plant itself (1).

A complementary role, not an alternative cancer treatment

When discussing phytotherapy and cancer, it is important to be very clear: plant-based preparations should not be used as an alternative to proven cancer treatment, since there is no good evidence that phytotherapy can replace evidence-based cancer treatments like radiotherapy or chemotherapy

However, some phytotherapeutic preparations may have a role as supportive care. This means they may help to relieve certain symptoms or side effects, or support quality of life, alongside standard cancer care.

This is where the current evidence is most relevant: not as a cancer cure, but as a possible way to help manage symptoms such as nausea or anxiety. The evidence for phytotherapy in oncology is still limited. Many studies are small, use different preparations, or measure different outcomes. This makes it difficult to draw strong conclusions. Still, some specific plant-based preparations have shown potential benefit for specific symptoms.

Plant-based options for symptom management

Ginger

For tackling nausea and vomiting, ginger has been studied in people receiving chemotherapy. Some studies suggest that ginger may help reduce chemotherapy-induced nausea or vomiting when used in addition to standard anti-nausea medication (2).

Peppermint

Peppermint essential oil, usually used through inhalation, has also been studied for nausea. A study found that peppermint aromatherapy may reduce nausea and vomiting in certain patients receiving chemotherapy (3).

Lavender

Lavender essential oil is often used in aromatherapy. Several studies have explored whether it can help with anxiety, stress, or sleep quality in people with cancer. The evidence suggests that lavender aromatherapy may have a positive effect on anxiety and sleep quality in some patients. This may be useful because cancer and cancer treatment can strongly affect emotional well-being and rest (4,5).

“Natural” does not automatically mean safe

A common misunderstanding is that plant-based products are harmless because they are natural. This is not true. Plants contain active chemical substances. That is precisely why they may have effects. But it also means they may cause side effects or interact with medicines. Therefore caution is always needed as herb-drug interactions are possible.

This is especially important for people with cancer, because cancer treatments often have a narrow safety margin. A product that changes how a cancer medicine is absorbed, broken down, or removed from the body could make the treatment less effective or increase side effects (6,7).

An example is St. John’s Wort (a herbal antidepressant) and certain chemotherapy drugs like docetaxel. When taken together, St. John’s Wort causes a decrease of docetaxel concentrations in the plasma, which results in reduced therapeutic effects or undertreatment.

Another issue is product quality. Plant-based products sold as supplements are not regulated in the same way as medicines. Depending on the product and the country, there may be less control over the exact content, dose, purity, stability, and contamination risks. See our blog on supplements for more information.

Talk to your healthcare team

The most important advice is simple: tell your doctor about any plant-based product you are using or considering. Open communication helps your healthcare team check whether a product is safe in your specific situation.

At Anticancer Fund, we believe patients deserve clear, evidence-based information. If you are considering phytotherapy or another complementary approach during cancer care, you can always contact our information service, My Cancer Navigator, for reliable, personalised guidance.

References

(1) BSMO conference on 07-02-2026, talk by Olivia Jansen, CIRM U Liège. Phytotherapy in oncology : Balancing therapeutic potential and safety in cancer supportive care

(2) Chang, Wen P, and Yu X Peng. “Does the Oral Administration of Ginger Reduce Chemotherapy-Induced Nausea and Vomiting?: A Meta-analysis of 10 Randomized Controlled Trials.” Cancer nursing vol. 42,6 (2019): E14-E23. doi:10.1097/NCC.0000000000000648

(3) Efe Ertürk, Nuriye, and Sultan Taşcı. “The Effects of Peppermint Oil on Nausea, Vomiting and Retching in Cancer Patients Undergoing Chemotherapy: An Open Label Quasi-Randomized Controlled Pilot Study.” Complementary therapies in medicine vol. 56 (2021): 102587. doi:10.1016/j.ctim.2020.102587

(4) Cheng, Hui et al. “Aromatherapy with single essential oils can significantly improve the sleep quality of cancer patients: a meta-analysis.” BMC complementary medicine and therapies vol. 22,1 187. 14 Jul. 2022, doi:10.1186/s12906-022-03668-0

(5) Mardani, Abbas et al. “A systematic review of the effect of lavender on cancer complications.” Complementary therapies in medicine vol. 67 (2022): 102836. doi:10.1016/j.ctim.2022.102836

(6) Vasques, Ana Carolina Sr et al. “The Use of Herbal Medicines Among Cancer Patients.” Cureus vol. 16,2 e53455. 2 Feb. 2024, doi:10.7759/cureus.53455

(7) Joshua, Tanvi. “Phytotherapy in Integrative Oncology: Assessing the Safety and Efficacy of Herbal Supplements in Cancer Treatment.” J Integr Oncol 13 (2024): 490.LinkedIn post suggestion