Rule out medically, first

Difficulty concentrating is one of the least specific symptoms in medicine, so the exclusion list is long and worth working through: **sleep apnoea** (the most frequently missed — snoring, daytime sleepiness), **anaemia**, **iron, B12 and vitamin D deficiency**, **hypothyroidism**, uncontrolled diabetes, and recent infections including post-viral syndromes. Dehydration and skipped meals produce the same effect within hours. Many medications — antihistamines, some antihypertensives, anxiolytics — list it as a side effect. A basic blood panel is the reasonable first step.

What is actually happening

Sustained attention depends on working memory — the mental space where you hold information active while working with it. Its capacity is small and shared: anything else occupying space takes it from the same pool.

Hence the effect that surprises people: worry consumes working memory directly. An unresolved concern doesn't wait quietly to one side — it runs in the background and cuts into available capacity. That is why an anxious person can't concentrate however hard they want to, and why trying to concentrate harder consumes more still.

The second factor is fragmentation. Every switch between tasks carries a re-engagement cost of several minutes. A day with thirty interruptions isn't a day with thirty minutes lost — it's a day in which attention never reached depth.

What it could be

Several possibilities, because this list is not a diagnosis. What separates them is in the detail below each.

Sleep deprivation
How to tell
By far the most common cause, and the most underestimated. The cognitive effect of a week at six hours a night is measurable and accumulates without the person feeling tired.
Anxiety
How to tell
You can concentrate on what's urgent but not on what's important. The mind runs to the same subjects, and evenings are worse. Worry occupies precisely the space you need.
Depression
How to tell
Concentration is poor for everything, including what you used to enjoy. Comes with anhedonia, slowing, and the sense that thinking itself is heavy. The onset is identifiable in time, unlike ADHD.
ADHD
How to tell
The pattern is lifelong rather than a change, and appears in at least two contexts — not only at work. The signature is the paradox: you can't concentrate on what's boring but drop into six-hour hyperfocus on what's interesting.
Burnout
How to tell
Context-bound: you think clearly at home and stall at the office. Accompanied by cynicism and the sense that effort no longer counts.

What helps now

Sleep, before any technique. No productivity method compensates for a chronic deficit. If you're consistently under seven hours, the rest of this list is secondary.

Short blocks, one thing at a time. Twenty-five minutes on one task, phone in another room — not merely face down. Its presence on the desk alone lowers cognitive performance measurably.

Get the worry out of working memory. Write down what's churning, with a time you'll return to it. A logged worry no longer needs to run in the background.

One written thing, not a list. A list of twenty tasks consumes attention just by being read.

Movement. Aerobic exercise has a direct, fast effect on attention — one of the few interventions that works the same day.

When to get help

Book an assessment if it has lasted more than a month with no obvious explanation, if it affects your work or studies, or if it comes with low mood. If the pattern is lifelong and shows up in every context, ask for an ADHD assessment — from a psychiatrist or clinical psychologist, not through an online questionnaire. **If thoughts of harming yourself appear, call 112.**