Checkpoint inhibitors like pembrolizumab, nivolumab, and atezolizumab have changed lung cancer treatment. They remove a brake on the immune system so T cells can attack cancer cells. But that same immune boost can cause side effects. Cancer fatigue is one of the most common. A 2021 review in PMC found that fatigue is a side effect of checkpoint inhibitor therapy. It comes partly from the inflammation that immune activation causes.
If you have already read about melatonin dosing for sleep, fatigue, and immune support during checkpoint inhibitor treatment, this article continues from there. Here we look at two plant compounds: quercetin and green tea extract (EGCG). Researchers are studying these for how they might help with immune function and fatigue during cancer treatment.
| Comparison Axis | Quercetin | Green Tea Extract (EGCG) |
|---|---|---|
| Primary active compound | Quercetin (flavonoid) | Epigallocatechin-3-gallate (EGCG, catechin) |
| Dose in published safety trials | Up to 1,000 mg/day orally for 12 weeks | 200 mg EGCG twice daily (400 mg/day) with food for 1 year |
| Proposed immune mechanism (preclinical) | IL-6/JAK2/STAT3 modulation; Treg cell reduction | PD-L1 expression inhibition in NSCLC cells; T cell activation |
| Current evidence level | Preclinical models and Phase I human trial (intravenous) | Preclinical – cell lines and animal models; limited human data |
| Primary safety concern | CYP450 drug interactions; kidney caution in at-risk patients | GI upset when taken fasted; liver enzyme elevation at higher doses |
| Bioavailability challenge | Low oral absorption; enhanced delivery forms under study | Chemically unstable; food co-administration improves tolerability |
Dose sources: quercetin from PubMed PMID 29127724; EGCG from PMC5340117. Mechanism sources: PMID 38714236 (quercetin) and PMC6222340 (EGCG).
Understanding Cancer-Related Fatigue During Immunotherapy
Cancer fatigue is not just being tired. Rest does not reliably help. It can last weeks or months during or after active treatment. A 2022 meta-analysis in PMC found that fatigue was more common in patients on standard chemotherapy than in those getting checkpoint inhibitors. That context matters, but it does not mean checkpoint inhibitor fatigue is mild or rare for the people living with it.
Researchers are starting to understand why this fatigue happens. A 2025 PMC study (PMC12485599) found specific immune patterns (types of cytokine activity) linked to fatigue in patients on checkpoint inhibitors. The Th1 immune pathway appears important. This matters when looking at compounds that change immune signals, because how they help and how they could harm can overlap.
Quercetin: What the Research Shows
Quercetin is a flavonoid found in onions, capers, kale, and apples. Cancer researchers study it for its antioxidant, anti-inflammatory, and immune-boosting properties. A 2025 PMC review found that quercetin works alongside chemotherapy agents to boost immune function. It can change cytokine pathways that affect how the immune system fights tumors.
A lab study (PMID 38714236) found that quercetin changed the IL-6/JAK2/STAT3 pathway in cancer models and reduced regulatory T cells, called Tregs. Tregs can stop the immune system from fighting tumors. Lowering Tregs is part of how checkpoint inhibitors work. These are lab and animal findings, not human trials in lung cancer patients, so they need careful interpretation.
An early Phase I trial (PMID 9816216) gave quercetin as an IV injection to cancer patients. Researchers saw evidence of tyrosine kinase inhibition in blood samples. This was one of the first human studies to show measurable biological effects at tolerated doses. The IV form is not available as a standard supplement, though.
For oral dosing and safety, a PubMed review (PMID 29127724) found that quercetin at up to 1,000 mg per day for 12 weeks did not cause toxicity in study participants. Longer use and higher doses have not been studied as well in humans. Quercetin formulations at 1,000 mg per serving match the dose studied for safety.
Green Tea Extract and PD-L1: The Immunotherapy Connection
Epigallocatechin-3-gallate (EGCG) is the main active compound in green tea extract. It has been studied for anti-inflammatory, antioxidant, and anti-cancer effects across many cancer types. A 2022 review in PMC looked at green tea and lung cancer specifically. It found that lab evidence was promising but that human trials are needed before we can draw conclusions about using it as a treatment.
One lab finding has caught researchers’ attention. A study (PMC6222340) found that EGCG stopped PD-L1 expression in A549 lung cancer cells. After EGCG treatment, IFN-gamma-induced PD-L1 mRNA and protein levels dropped by 40 to 80 percent. PD-L1 is the same protein that checkpoint inhibitors like atezolizumab and durvalumab target. The same study found that EGCG also restored interleukin-2 in tumor-specific T cells in lab experiments, suggesting it might activate T cells. These are lab results; they do not prove EGCG helps humans with cancer.
A 2025 PMC study (PMC11954466) confirmed that EGCG triggered cell death in lung cancer cells through multiple pathways. Both studies note that these results come from lab models. Human trials testing EGCG with checkpoint inhibitors in lung cancer patients have not yet been published.
Talk with your pharmacist about which green tea extract formulation fits your current treatment plan before starting use.
Bioavailability: A Practical Concern
Both quercetin and EGCG have one big problem: the human gut does not absorb them well or consistently. Only a small amount reaches the bloodstream at levels that can be measured.
EGCG is chemically unstable. A clinical review (PMC3189735) found that poor absorption is a major reason why EGCG clinical results have been mixed. Its instability prevents it from reaching the levels that worked in lab studies. When green tea extract is taken on an empty stomach, nausea and stomach upset are more likely. A one-year safety trial (PMC5340117) tested a decaffeinated catechin mixture with 200 mg of EGCG twice daily, taken with food. It was well tolerated over 12 months with no treatment-related side effects. Taking it with food appears to reduce stomach risk without harming absorption.
Quercetin also has low oral absorption. A pharmacology review (PMC10674654) found that this limits its clinical use. Researchers are working on better delivery forms, including phytosome complexes and nanoformulations. The type of formulation matters as much as the milligram count on the label when choosing a product.
Talk with your care team or pharmacist about which formulation might work for you.
Safety and Drug Interaction Cautions
Both compounds have risks for patients on active cancer treatment. Talk with your oncologist before using either one.
Quercetin can affect CYP450 liver enzymes and drug transport proteins. Many oral cancer drugs, including targeted therapies, depend on these pathways to be processed and removed from the body. Changes to enzyme activity could raise or lower drug levels in the blood. The safety review (PMID 29127724) also warned of possible kidney toxicity in patients with existing kidney damage. Patients with hormone-sensitive cancers should ask their oncologist about quercetin, because some animal studies show effects on estrogen-dependent pathways.
High-dose green tea extract has been linked to elevated liver enzymes. The Minnesota Green Tea Trial (PMC4540665) studied high-dose green tea extract in postmenopausal women at risk for breast cancer. Some participants had signs of liver toxicity at high doses. Patients with existing liver problems or those taking drugs processed by the liver should ask their pharmacist or oncologist before using any green tea extract.
The immune-changing properties that make these compounds interesting are the same properties that could interact with checkpoint inhibitors. That is not a reason to avoid them, but it is a reason to talk with your oncology team before starting.
To see how another anti-inflammatory supplement is being studied for cancer side effects, read our article on whether curcumin may help with chemotherapy-related peripheral neuropathy and at what dose.
Practical Steps for Patients and Caregivers
- Tell your oncologist and pharmacist about all supplements before starting anything during active immunotherapy.
- If you take oral targeted therapies with a checkpoint inhibitor, talk with your oncologist about quercetin because of its CYP450 effects.
- Take green tea extract with food to reduce the risk of stomach upset and liver enzyme changes.
- Stay within the dose range studied in safety trials: up to 1,000 mg per day for oral quercetin; up to 400 mg EGCG per day based on the one-year safety trial cited above.
- Fatigue during immunotherapy can come from many causes, including anemia, thyroid problems, and sleep loss. Get a full evaluation from your doctor before adding supplements.
If you are currently taking prescription medication, are pregnant, or are breastfeeding, speak with a clinician before using any supplement discussed in this article. This article is for general information and is not a substitute for medical advice. Always consult your oncologist or care team about your specific situation.
