All 16 women who completed a UCLA trial of oxaloacetate reported better cognition, with scores moving from the impaired range into the normal range. The researchers are explicit that the design cannot show cause.

Among the lasting complaints of breast cancer survivors is one that medicine has little to offer for. Patients call it chemo brain or brain fog: difficulty concentrating, words that will not come, a sense of thinking through treacle, which can persist for years after treatment ends. An estimated 15 to 25 per cent of breast cancer survivors have persistent cognitive difficulties.

Researchers at UCLA Health’s Jonsson Comprehensive Cancer Center have published results from a small trial of a dietary supplement for the problem, and the outcome was striking: all 16 women who completed the study reported significant improvement.

The authors are careful about what that does and does not mean. The trial had no placebo group, and with 18 women enrolled it is too small to establish much.

“Cancer-related cognitive impairment can persist long after treatment ends,” said Dr Patricia Ganz, a distinguished professor of medicine at the David Geffen School of Medicine at UCLA and the UCLA Fielding School of Public Health, and the paper’s first author. The condition can significantly affect daily life, she noted, and there are very few effective treatments for it.

A molecule from the energy cycle

The compound tested is oxaloacetate, a molecule the body makes itself as part of how cells produce energy. It is an intermediate in the citric acid cycle, the series of reactions by which cells extract energy from food.

The rationale for testing it rests on two of its roles. Cancer and its treatments may provoke inflammation that disrupts both normal glutamate signalling in the brain and cellular energy production. Glutamate is the brain’s main excitatory neurotransmitter, and oxaloacetate participates in its regulation, as well as in energy metabolism. A compound touching both processes was therefore worth a look.

That is a plausible chain of reasoning rather than a demonstrated mechanism, and the release presents it as the reason for the trial rather than as a finding.

Eighteen women, eight weeks

The phase II trial enrolled 18 women with early-stage breast cancer who were one to five years past diagnosis and reported significant cognitive difficulties. Their average age was about 50. Most had received chemotherapy, and nearly 90 per cent were taking endocrine therapy during the study.

They took 500 mg of oxaloacetate twice daily for eight weeks.

Assessment came in two forms. Participants filled in questionnaires about their own cognitive symptoms, and they also completed standardised neuropsychological tests of attention, memory, processing speed and executive function. Fatigue, sleep, anxiety, depression and physical and mental health were measured as well.

The distinction between the two kinds of measure matters in this field, because perceived and measured cognition often diverge. Patients frequently report difficulties that formal testing does not detect, which has made cancer-related cognitive impairment contentious: real to those who have it, hard to pin down in a clinic.

Causes of the impairment are still debated. Chemotherapy is the usual suspect, and the colloquial name reflects that, but cognitive difficulties also appear in patients treated with surgery and endocrine therapy alone, and sometimes before treatment begins. Inflammation, hormonal change, fatigue, sleep disruption and the psychological weight of a cancer diagnosis have all been implicated.

From impaired to normal

Sixteen of the 18 participants finished the eight weeks. All 16 reported significant improvement in cognitive symptoms.

The primary measure, a score for perceived cognitive impairment, rose from 29.1 before treatment to 55.5 afterwards, which moved the group from the impaired range into the normal range. Improvements were already visible at four weeks and generally grew larger by the end.

Other measures moved too. Fatigue, including mental fatigue, decreased significantly, and physical functioning improved significantly. On the objective tests, executive function and processing speed improved, which the researchers describe as preliminary given the sample size.

Side effects were mostly gastrointestinal. Two participants stopped treatment because of them, and no serious adverse events were reported.

Why the missing placebo matters so much here

The researchers state plainly that without a placebo or comparison group, the study cannot show that oxaloacetate caused the improvements. That caveat deserves more weight than such caveats usually get.

Self-reported symptoms are among the outcomes most susceptible to placebo effects. A woman who has struggled with brain fog for years, who enrols in a trial, takes a supplement twice daily and answers questionnaires about how her thinking feels, has every reason to report improvement whether or not the compound does anything. Regression to the mean compounds the problem: participants were recruited because they reported significant difficulties, and people selected at a low point tend to score better later regardless of treatment.

Fatigue and physical functioning are similarly open to expectation. The improvements in executive function and processing speed on formal testing are harder to explain that way, but repeated neuropsychological testing produces practice effects, since people get better at tests they have taken before.

None of this means the supplement does nothing. It means a single-arm trial of 16 completers cannot distinguish a drug effect from the several other explanations available, which is precisely why the next study is designed differently.

What comes next

A randomised, placebo-controlled phase II trial is expected to open in late 2026, and preclinical mouse studies are under way to work out how oxaloacetate might act.

That is the right sequence. A randomised trial with a placebo arm would show whether the improvement exceeds what a dummy capsule produces, and animal work could establish whether the proposed mechanism is real.

“These early findings give us a strong reason to continue studying oxaloacetate,” Ganz said, describing it as a potential approach to managing cognitive problems after breast cancer treatment.

The framing is accurate: a reason to continue studying, not a treatment. Oxaloacetate is sold as a dietary supplement, which means it is available without prescription and without the evidence of efficacy a drug approval would require. Survivors reading about these results may be tempted to buy some, and the honest summary is that nobody yet knows whether it works.

Ganz’s co-authors were Kathleen Van Dyk, Catherine M. Crespi, Laura Petersen, Mina Sedrak and Julienne Bower. The work was funded by the National Cancer Institute and the Breast Cancer Research Foundation.

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Notes

1. Ganz, P., et al. JCO Oncology Advances, 2026. DOI: 10.1200/OA-26-00063.
2. University of California – Los Angeles Health Sciences. “Nutritional supplement may help ease ‘brain fog’ after breast cancer treatment.” EurekAlert!, 20 October 2026. https://www.eurekalert.org/news-releases/1148117.