A Familiar Drug With an Unexpected Second Role
Valproic acid (VPA) has been around for decades. Most people know it as an anti-seizure medication — and for good reason. Seizures affect an estimated more than 25% of patients with high-grade glioma, making seizure control a key concern from the moment of diagnosis. Valproic acid is one of the two most commonly prescribed anti-seizure medications for brain tumor-related epilepsy.
But researchers have noticed something worth paying attention to. Patients taking VPA alongside standard chemoradiation — temozolomide (TMZ) plus radiation — sometimes appear to do better than patients on other anti-seizure drugs. That pattern, repeated across multiple datasets, has driven laboratory and clinical research into a straightforward question: could VPA be doing more than just preventing seizures?
This article explains the biological rationale, reviews the clinical evidence for and against a genuine anti-tumor effect, outlines the real risks of VPA, and helps you frame the right conversation with your neuro-oncologist.
What Is Valproic Acid, and Why Does It Interest Oncologists?
VPA is a short-chain fatty acid used for decades as an anti-seizure medication and mood stabilizer. It controls seizures by boosting GABA (a calming neurotransmitter), blocking certain ion channels, and reducing excitatory neurotransmission in the brain.
What oncologists find interesting is a separate property: VPA belongs to a class of molecules called histone deacetylase (HDAC) inhibitors, which target the epigenetic control of gene function in cancer cells. That mechanism has nothing to do with seizure suppression, and it has direct implications for how tumor cells grow, divide, and resist treatment.
The Biology: How VPA May Act Against Glioblastoma Cells
To understand the research excitement, it helps to know a little about epigenetics. Genes are wrapped tightly around proteins called histones. Whether a gene turns on or off depends partly on chemical tags attached to those histones. HDAC enzymes remove one type of tag — the acetyl group — and when they are overactive, they can silence tumor-suppressor genes and fuel cancer growth.
In glioblastoma cell lines and animal models, VPA has shown several potentially anti-tumor effects:
- Slowed cell growth: VPA inhibits cell proliferation by causing cell-cycle arrest in the G1 and/or G2 phase and induces differentiation and/or apoptosis in cancer cells. It has also reduced proliferation in glioblastoma-derived stem cells.
- Reduced invasion: VPA has been shown to affect tumor cells by inhibiting proliferation, angiogenesis, and promoting apoptosis. In preclinical glioma models, it may also block tumor cells from invading surrounding healthy tissue.
- Radiosensitization: Several in vivo and in vitro studies have indicated that VPA has radiosensitizing effects for gliomas and radioprotective influence on normal brain tissue or hippocampal neurons. It may help radiation kill more tumor cells while potentially shielding healthy brain.
- TMZ sensitization: In the laboratory, VPA was suggested to downregulate the expression of MGMT — the DNA-repair protein that helps tumors resist temozolomide — and to sensitize human glioma cells to temozolomide and irradiation.
- Apoptosis via mTOR pathway: Research published in a peer-reviewed journal found that VPA may promote programmed cell death in glioma through Akt/mTOR signaling, a key growth pathway in many cancers.
It is worth noting that the in vitro effects of VPA are weak and largely variable depending on cell line, dose, and time of exposure. Lab findings do not always carry over to human patients, which is why clinical evidence matters.
There is also a concern worth understanding. Because VPA has DNA-demethylation properties, it may also increase MGMT expression in some tumor cells — an effect that could reduce TMZ sensitivity. This is one reason the science stays unresolved. Your molecular profile, particularly your MGMT methylation status, may affect how relevant this concern is in your case.
IDH-Mutant Gliomas: A Possible Area of Selectivity
One promising line of preclinical research involves tumors with an IDH1 mutation, a molecular subtype more common in lower-grade gliomas that can progress to GBM. VPA, a brain-penetrant anti-seizure medication and HDAC inhibitor, inhibits the growth of IDH1-mutant tumors in vivo and in vitro, with at least some selectivity over IDH1 wild-type tumors. The proposed mechanism involves disruption of lipid metabolism in IDH1-mutant cells specifically — a lead researchers are still working to confirm. For more on how IDH and other molecular markers shape treatment options, see our guide to understanding your GBM molecular profile.
What the Clinical Studies Show
The most frequently cited clinical signal came from a post-hoc analysis of the landmark EORTC/NCIC temozolomide trial — the same trial that established TMZ plus radiation as the standard of care for GBM. In that analysis, patients receiving VPA showed prolonged survival over those receiving other enzyme-inducing or no anti-seizure drugs. This was an observational finding, not a randomized comparison, but it was striking enough to drive further investigation.
A Phase II trial at the National Cancer Institute tested VPA as an add-on to standard RT and TMZ in 37 newly diagnosed GBM patients. VPA was shown to sensitize GBM cells to radiation in preclinical models, which was the rationale for evaluating its addition to standard therapy. A later comparative analysis involving the NCI trial, the RTOG 0525 dataset, and SEER population data found that the percent of patients surviving an additional 12 months (from a 6-month landmark) was 77% in the NCI study, compared to 57% in RTOG 0525 and 43% in SEER — differences that were statistically significant at multiple time points, though the studies are not directly comparable.
A systematic review and meta-analysis published in Annals of Oncology pooled data from eight cohort studies involving 5,786 glioblastoma patients. The pooled results found a statistically significant association between valproic acid use and overall survival, with a pooled hazard ratio of 0.81 (95% CI 0.74–0.88). A hazard ratio below 1.0 suggests a survival benefit — here, roughly a 19% reduction in the risk of death at any given time point for VPA users. Most included studies were retrospective, however, and could not rule out confounding factors.
On the other side, a large prospective pooled analysis published in the Journal of Clinical Oncology — drawing on several EORTC trials — raised questions about whether VPA or levetiracetam truly improve survival in GBM, noting that AED use at study entry only was used for the analysis, a meaningful limitation since the data may have missed patients who switched drugs mid-treatment.
Retrospective evidence is largely encouraging. Prospective trial data is mixed. There is currently an ongoing debate on whether the putative beneficial VPA effects in glioblastoma should be tested in a prospective randomized clinical trial. That trial has not been completed. Until it is, VPA's anti-tumor role in GBM remains biologically plausible but clinically unproven.
For patients interested in other repurposed drugs being studied alongside standard GBM therapy, our articles on metformin in GBM, chloroquine and autophagy inhibition, and tamoxifen repurposing cover related areas of active investigation.
Seizure Control: Still the Primary Role
Whatever the final verdict on VPA's anti-tumor effects, its role in seizure management is real and clinically significant. Brain tumor-related epilepsy occurs in an estimated more than 25% of high-grade glioma patients, and VPA is one of two first-line anti-seizure medications for this condition. Uncontrolled seizures carry serious risks — injury, hospitalizations, and reduced quality of life. Even if VPA's anti-tumor benefits are modest or unproven, seizure control alone can justify its use in eligible patients.
It is also worth knowing that use of VPA has decreased in recent years because of a broader side effect profile, potential interactions with chemotherapy drugs, and the availability of newer-generation agents such as levetiracetam. Your neuro-oncologist will weigh these factors against your overall treatment plan.
Known Risks and Side Effects
VPA is not a gentle drug. A clear-eyed look at its side effect profile is essential before anyone considers it in the GBM context.
Common side effects include:
- Nausea, vomiting, and abdominal discomfort
- Tremor and drowsiness
- Hair thinning (alopecia)
- Weight gain
- Dizziness and cognitive fogginess
Serious risks to monitor:
- Thrombocytopenia: The frequency of adverse effects, particularly elevated liver enzymes and thrombocytopenia, may be dose-related. A drop in platelets raises bleeding risk, which is a concern when patients are also receiving temozolomide, which affects bone marrow independently.
- Liver toxicity: Common short-term reactions include gastrointestinal, neurologic, and hematologic adverse effects such as thrombocytopenia, while more severe but less frequent reactions can include hepatotoxicity leading to liver failure. Regular liver function monitoring is standard practice.
- Hyperammonemia: Elevated ammonia in the blood can cause confusion or lethargy — symptoms that may be mistaken for tumor progression. Any new neurological change in a patient on VPA should prompt evaluation.
- Drug interactions: VPA can interact with temozolomide and other drugs commonly used in GBM care. Your pharmacist and oncology team should review your full medication list.
- Pregnancy: VPA carries a black box FDA warning for fetal harm, including neural tube defects and lower IQ in children exposed before birth. Women of childbearing potential must discuss this risk carefully with their care team.
A Phase II trial follow-up at the NCI reported a favorable safety picture in long-term survivors, noting that the addition of VPA to concurrent RT/TMZ was well tolerated with little late toxicity, with most adverse events being grade 1 or 2. There were only two grade 3/4 toxicities in long-term survivors. Still, this was a small, selected cohort and does not represent all patients.
Where Does VPA Fit in an Integrative Oncology Strategy?
VPA is a pharmaceutical agent with measurable biological activity and real risks — not a supplement or lifestyle intervention. For patients already prescribed VPA for seizure control, the relevant question is whether its potential anti-tumor properties offer an added benefit. For patients not yet on VPA who are thinking about asking, the decision involves weighing seizure risk, drug interactions, side effect tolerance, and molecular profile.
Patients interested in integrative oncology strategies may also want to explore complementary evidence-based approaches alongside standard treatment. Our overview of integrative treatments for glioblastoma covers a range of approaches — from the ketogenic diet to hyperbaric oxygen to curcumin — studied as adjuncts to standard care. None of these replace surgery, radiation, and chemotherapy; they are investigated as additions to that foundation.
If clinical trials interest you, an active trial evaluating VPA combined with other repurposed agents in recurrent high-grade glioma exists (NCT01817751). Ask your neuro-oncologist whether you or your loved one might be eligible, or search ClinicalTrials.gov for currently enrolling studies.
When to Talk to Your Doctor
Bring up valproic acid with your neuro-oncologist if:
- You already have seizures and are deciding between anti-seizure medications
- You want to know whether your MGMT methylation status or IDH mutation status affects VPA's potential relevance for you
- You are interested in drug repurposing as part of a broader integrative strategy and want evidence-based guidance
- You are already on VPA and want to know whether it should stay in your regimen during and after chemoradiation
- You develop new symptoms — confusion, unusual fatigue, easy bruising, or yellowing of the skin — while taking VPA
Do not start, stop, or adjust VPA on your own. Changes to anti-seizure medications require careful medical supervision, including blood monitoring and coordination with your full oncology team.
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.