Two different effects
A sharp, brief stress response can actually sharpen memory for the event itself. That is familiar: people recall emotionally charged moments vividly, sometimes more vividly than they recall them accurately.
Sustained stress does something close to the opposite. Prolonged elevation of cortisol is associated with impaired performance on exactly the kinds of memory task people complain about — forming new memories and retrieving existing ones under pressure.
The mechanism, roughly
The hippocampus, central to forming new episodic memories, is unusually dense in receptors for cortisol, which makes it responsive to the stress system in a way most tissue is not. Animal work shows structural changes under chronic elevation, and human imaging work points in a similar direction, with the important caveat that causality in human studies is hard to establish.
There is also a far simpler contribution that gets overlooked. Stress occupies attention. A person running a continuous background process about a sick relative or a precarious job has less attention available for the name of somebody they met at a party, and the name was therefore never properly encoded in the first place.
Why this one is good news
Of all the causes of memory complaints, this is among the most reversible. When the stressor resolves, or when it is managed, the symptoms generally improve. People describe it as a fog lifting over weeks rather than a switch flipping.
It is also worth naming the loop: worrying about your memory is itself a stressor, and sustained worry about memory can make memory worse. Several people arriving at this topic are further along that loop than they realise.
What actually helps
- Sleep first. Stress and sleep degrade each other, and sleep is the more tractable end of that loop for most people.
- Movement, again. One of the better-evidenced interventions for the stress response itself, as well as for everything else on this site.
- Write things down and stop holding them. Externalising the running list reduces the load the background process is carrying.
- Treat the worry as a symptom too. If anxiety about memory has become its own problem, that is worth raising at an appointment rather than managing alone.
Where a supplement does not fit
Nothing on this shelf addresses a stress response, and anybody selling a brain supplement as a solution to a hard year is selling the wrong thing. If the memory complaints began alongside a period of genuine strain, the strain is the thing to deal with.