Many people undergoing cancer treatment look for additional ways to support their health. Herbal medicines, plant extracts and other natural products are frequently part of that search. But can phytotherapy be used alongside chemotherapy, hormone therapy, targeted therapy or immunotherapy?
The answer is not simply yes or no.
Phytotherapy is increasingly studied within the broader field of integrative oncology — not only for supporting wellbeing and managing treatment-related symptoms, but also for the potential biological effects of plant compounds on processes involved in cancer itself.
At the same time, medicinal plants contain biologically active substances. This means that potential benefits and potential interactions with cancer medicines need to be considered together.
Rather than automatically avoiding phytotherapy during cancer treatment, the important question is therefore:
What can safely and meaningfully complement this particular patient’s treatment?
Complementary, Not Alternative
There is an important distinction between using phytotherapy instead of evidence-based cancer treatment and using carefully selected phytotherapeutic approaches alongside conventional treatment.
The latter fits within the growing field of integrative oncology, which brings evidence-informed complementary approaches together with conventional cancer care.
Cancer treatment itself — whether surgery, chemotherapy, radiotherapy, hormone therapy, targeted therapy or immunotherapy — remains the foundation of care. Phytotherapy should not be presented as a replacement for it.
But that does not mean medicinal plants have no place in oncology.
More Than Symptom Support
One role of phytotherapy is supportive care. Cancer and its treatments can cause fatigue, digestive discomfort, nausea, changes in appetite, sleep difficulties and other symptoms that significantly affect quality of life. Complementary approaches are increasingly studied and, for certain symptoms, incorporated into integrative oncology.
However, scientific interest in phytotherapy extends beyond helping patients cope with the side effects of treatment. Plants contain thousands of biologically active compounds, including polyphenols, flavonoids and terpenoids. A growing body of research is investigating how certain phytochemicals may influence biological processes involved in the development and progression of cancer itself.
In laboratory and animal research, plant-derived compounds have demonstrated effects on processes such as:
- cell proliferation and cell-cycle regulation
- programmed cell death (apoptosis)
- inflammatory signalling
- oxidative stress
- angiogenesis
- tumour-related signalling pathways
- mechanisms involved in treatment resistance
Researchers are also studying whether selected phytochemicals could complement conventional anticancer therapies. In some experimental models, combinations have produced additive or synergistic effects, raising the possibility that certain botanical compounds may eventually have a role as adjuncts to established treatments.
This idea is not as unusual as it may sound. Nature has provided the pharmacological starting point for several important cancer medicines. The vinca alkaloids and taxanes, for example, originated from plants. While many findings are promising, their clinical relevance depends on factors such as formulation, dose and metabolism, and continues to be explored in human research.
Biological Activity: Potential Benefit and Potential Interaction
The same biological activity that makes phytotherapy interesting in cancer research is also why interactions with medication need to be considered. Many cancer medicines require carefully controlled concentrations in the body. Certain herbal compounds can influence enzymes and transport proteins involved in drug metabolism, including the cytochrome P450 enzyme system and P-glycoprotein. This means that a botanical product may potentially increase or decrease exposure to a cancer medicine.
One of the best documented examples is St John’s wort (Hypericum perforatum). St John’s wort influences CYP3A4 and P-glycoprotein activity. Human studies have shown that it can reduce exposure to certain anticancer medicines, including irinotecan and imatinib. In such cases, taking a natural product alongside treatment could potentially reduce the effectiveness of the medicine.
But interaction does not automatically mean that two treatments oppose one another.
Researchers are also investigating botanical compounds and formulations precisely because some may potentially complement or enhance particular anticancer treatments. One example is PHY906, a standardized botanical formulation derived from a traditional Chinese herbal formula that has been studied as an adjunct to conventional cancer therapy.
The key point is that these effects are specific. A finding for one botanical and one medicine cannot be generalized to phytotherapy as a whole.
Why the Cancer Treatment Matters
Chemotherapy, targeted therapy, hormone therapy and immunotherapy work through very different mechanisms. A botanical that is appropriate in one situation may therefore be unsuitable in another.
Antioxidants illustrate this complexity well. Plant compounds with antioxidant properties are often considered beneficial, yet some cancer treatments partly depend on oxidative mechanisms to damage cancer cells. Research into concentrated antioxidant supplementation during cancer treatment has produced mixed results, and there is currently insufficient evidence to make a universal recommendation. Importantly, eating antioxidant-rich fruits, vegetables, herbs and spices as part of a varied diet is very different from taking highly concentrated extracts.
Immunotherapy raises different questions. Immune checkpoint inhibitors deliberately modify the interaction between the immune system and cancer cells, while numerous phytochemicals can influence immune signalling. Compounds including curcumin, resveratrol and others are being actively investigated for their effects on cancer-related pathways and their potential interactions with conventional therapies. However, much of this research remains preclinical. This is why broad descriptions such as “antioxidant” or “immune boosting” are not enough to determine whether a product is appropriate during cancer treatment.
The plant, formulation, dose and specific cancer treatment all matter.
Communication Is Essential
Many people already use vitamins, supplements or herbal products when they receive a cancer diagnosis. Others begin using them during treatment. Yet patients do not always tell their oncology team.
If patients expect complementary medicine to be dismissed automatically, they may simply stop mentioning what they are taking. That makes it more difficult to identify potentially important interactions — or to have an informed discussion about approaches that might be compatible with their treatment.
Ideally, phytotherapy should be evaluated together with the oncologist, treating physician or oncology pharmacist and, most desirable, a healthcare professional knowledgeable about phytotherapy.
Sometimes a botanical may be considered appropriate alongside treatment.
Sometimes the dose or timing may need to be adjusted.
Sometimes it may be preferable to stop it during a particular treatment phase.
And sometimes there simply is not enough evidence to know.
These decisions need to be made for the individual combination rather than for “phytotherapy” as a single category.
Considering Phytotherapy During Cancer Treatment?
A few principles can help:
- Tell your treating physician what you are taking. Include herbal extracts, teas, vitamins and supplements.
- Provide the exact formulation and dose. “I take turmeric” is much less informative than providing the exact extract, concentration and daily dose.
- Consider the specific treatment. Compatibility cannot be determined without knowing which anticancer therapy is being used.
- Do not assume that more is better. Concentrated botanical extracts can behave very differently from the quantities normally consumed as food.
- Seek knowledgeable guidance. Ideally, decisions should involve professionals familiar with both the cancer treatment and the pharmacology of the botanical ingredients.
- Reassess when treatment changes. A product considered appropriate at one stage may need to be reconsidered when medication or treatment protocols change.
The Bottom Line
Phytotherapy and conventional oncology do not necessarily have to exist in opposing worlds. Medicinal plants are being investigated both for their role in supporting patients through cancer treatment and for the biological activity of their compounds in cancer-related processes and as potential adjuncts to conventional therapy. That does not mean a promising phytochemical can be assumed to treat cancer, nor that every botanical can safely be combined with every cancer medicine. But neither does cancer treatment automatically mean that all phytotherapy must be avoided. The more useful approach is an individualized one: consider the evidence for the specific botanical, formulation and dose alongside the specific cancer treatment, and make that decision openly with the treating healthcare team.
If you are undergoing cancer treatment and considering a herbal product or supplement, always discuss the exact product and formulation with your healthcare provider before starting or stopping it.
REFERENCES
National Cancer Institute. Cancer Therapy Interactions With Foods and Dietary Supplements (PDQ®). National Cancer Institute.
National Cancer Institute. Complementary and Alternative Medicine (CAM). National Cancer Institute.
Aljabali AAA, Obeid MA, Bashatwah RM, et al. Phytochemicals in Cancer Therapy: A Structured Review of Mechanisms, Challenges, and Progress in Personalized Treatment. Chemistry & Biodiversity. 2025;22(8):e202402479.
Theunissen I, Bagot JL. Supportive cancer care: is integrative oncology the future? Current Opinion in Oncology. 2024;36(4):248–252.
Carlson LE, Tripathy D, Zick SM, et al. The Society for Integrative Oncology–American Society of Clinical Oncology Joint Guidelines on Integrative Therapies for Symptom Management: Overview and Key Recommendations. Journal of Integrative and Complementary Medicine. 2024;30(7):596–601.