Chemo Brain, Explained: What’s Actually Going On?

Cancer and Cognition: What’s Going On—and What Can Help?

Cancer affects us in ways that go far beyond the physical. For many people, the experience of going through cancer treatment is one of the most challenging periods of their lives. It's not just the fatigue, the medications, or the disruption to everyday routines—it can also affect how we think, remember, and concentrate.

These kinds of cognitive changes in cancer survivors are often described informally as “chemo brain.” It’s a term that originated with patients themselves—many of whom felt their experiences were initially dismissed or misunderstood. While “chemo brain” isn’t a scientific term, it reflects something very real for a subset of people: noticeable changes in thinking ability during or after cancer treatment.

In recent years, research has helped us understand more about cancer and brain function, how common chemo brain symptoms are, and what can be done about it.

What kinds of cognitive problems can happen after cancer?


Most people who report cognitive symptoms after cancer treatment describe issues with:

These issues are often subtle rather than dramatic. But even mild changes can feel frustrating, especially for people who previously felt sharp, high functioning, and mentally quick.

What causes these changes?

The picture is complex. We used to think cognitive problems were mostly a side effect of chemotherapy—but we now know that’s only part of the story. A more technically accurate term than chemo brain fog is cancer-related cognitive impairment (bit of a mouthful though!), because these changes can arise from a number of sources:

  • Chemotherapy: Traditional chemotherapy agents target rapidly dividing cells, which unfortunately includes not just cancer cells but also cells that support brain health. Some chemotherapy drugs are known to be neurotoxic and may impact the brain indirectly by triggering inflammation or reducing neuroplasticity.
  • Immune and inflammatory responses: Chemotherapy can increase inflammatory markers (like cytokines) that affect the brain. This can lead to subtle but real changes in how the brain functions—even if the chemotherapy drugs themselves don’t cross the blood-brain barrier.
  • Radiation therapy: Radiation to the body can have systemic effects, and radiation to the brain (e.g. for metastases) carries a particularly high risk of cognitive side effects. Even with modern techniques, such as hippocampal-sparing radiation, there can be lasting impact.
  • Hormonal therapies: For example, androgen deprivation therapy used in prostate cancer has been linked to changes in visuospatial functioning, although this area is still being researched.
  • The cancer itself: While cancer that hasn’t spread to the brain is unlikely to directly impair cognition, the illness and its systemic effects may still play a role—especially in advanced or aggressive cancers.
  • Psychological factors: Understandably, people undergoing cancer treatment often experience high levels of stress, anxiety, fatigue, and poor sleep. These factors alone can affect memory and concentration. For some, the trauma of the cancer experience itself may also contribute to how they feel and function cognitively.

How common is it?

Estimates vary widely, depending on how the data is collected. Studies that rely on self-report tend to find higher rates—sometimes up to 70% of people say they notice cognitive changes during or after treatment. When more structured testing is used, around 15% to 25% of patients show measurable cognitive difficulties during or after treatment.

Importantly, not everyone is affected the same way. Some people feel significantly impaired, while others may not notice any changes at all. We’re still learning why these individual differences occur, but factors like age, cognitive reserve, type of cancer, and treatment intensity may all play a role.

Do cognitive problems improve over time?

For many people, yes. Cognitive symptoms often improve once treatment finishes. But for a meaningful minority, these difficulties can persist—sometimes even years later. A small number of people may find their cognitive function worsens over time, although this is less common.

It’s also worth noting that the perception of cognitive decline doesn’t always match what shows up on testing. People’s own experience of their cognition—filtered through fatigue, anxiety, or loss of confidence—can sometimes differ from what formal assessments detect.

That doesn’t mean their concerns aren’t very valid and real. On the contrary, it means we need to approach these concerns with care, clarity, and curiosity to ensure they have the support they need to navigate the challenges they are noticing day-to-day.

What can be done?

There’s no one-size-fits-all solution, but there are steps that can make a meaningful difference in post-cancer cognitive support.

  • Understanding what’s happening is often the first step. Many people feel reassured to know that what they’re experiencing is recognised and has a name. Just being told “this is real, and you’re not imagining it” can be powerful.
  • A structured cognitive assessment can help to identify strengths and vulnerabilities. It can clarify whether there is evidence of change, and if so, what type—and what might be driving it.
  • Practical strategies can often help. These might include ways to support memory, improve mental energy, reduce overwhelm, and work with your current strengths rather than against them.
  • Physical activity has consistently been shown to support recovery—not just physically, but cognitively. It may feel counterintuitive when you’re fatigued, but gentle movement (especially if started gradually) can have wide-ranging benefits.
  • Addressing sleep, stress, and mood is essential. These aren’t secondary concerns—they’re core parts of your cognitive health. Supporting emotional wellbeing and reducing fatigue can often lead to improvements in concentration and memory.

When to seek help

If you’ve been through cancer treatment and are noticing changes in your memory, focus, or mental clarity—and those changes are persisting or affecting your confidence—it may be time to check in.

In my clinical practice, I offer a Cognitive Health Review that is specifically designed for situations like this. It’s not about pathologising normal experiences or overtesting—it’s about helping people understand what’s happening, what’s not, and what might help.

You don’t need to be at crisis point to benefit and you don’t need a specialist referral to access this. Some people come in for reassurance, others are looking for support to manage at work or make adjustments in their daily lives. Whatever the reason, the process is collaborative and tailored to your needs.

Closing thoughts

Cancer survivorship isn’t just about being disease-free. It’s about recovering, rebuilding, and finding ways to move forward. For some people, that includes navigating changes in how they think and function cognitively.

These changes may be subtle. They may be hard to explain to others. But they matter—and they’re worth understanding. I’ve put together a free thinking skills self-check if you would like to take a first step towards better understanding. 

📥 Download the Thinking Skills Self-Check

If this post resonates with your experience, you’re very welcome to get in touch.

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