What brain fog actually is
Brain fog is the everyday name for a cluster of small cognitive slips, losing a word mid-sentence, walking into a room and forgetting why, finding it harder to hold your concentration or juggle several things. During perimenopause these are common, and they are tied to the same hormonal fluctuations driving the rest of the transition.
The important thing is that this is a genuine, documented change, not a character flaw or a sign you are failing to cope.
The reassuring part, and it is well evidenced
An updated systematic review and meta-analysis of cognition across perimenopause found that women in the transition do test slightly lower than before it, but, notably, no worse than, and on some measures better than, women who are already postmenopausal (Psychology and Aging, 2025). In other words, the dip appears to be a feature of the transition itself, and cognition tends to settle again on the other side.
That is a very different story from a steady decline. Perimenopausal brain fog looks like a temporary state, not a trajectory.
When it is worth a closer look
Being reassured is not the same as being dismissed. Brain fog at this stage does not signal dementia, but persistent or worsening cognitive problems, especially ones that interfere with work or daily life, deserve attention rather than a shrug (Climacteric, 2022). Poor sleep, low mood, thyroid problems, and other treatable things can all cloud thinking too, and they are worth ruling out.
When to talk to a GP
See your GP if the fog is severe, getting steadily worse, affecting your ability to do your job or manage daily life, or coming with other symptoms that worry you. A conversation can rule out other causes and, where appropriate, cover whether treatment options are right for you. anna does not diagnose, and this article is not medical advice.