Stroke is the single largest cause of neurological disability in the world. It is also, according to the largest study of its kind, about 90% attributable to risk factors you can do something about.
Two parts to this, and they operate on completely different timescales: what to do in the next four minutes, and what to do over the next four decades.
The four signs — FAST
If you see any one of these, call an ambulance immediately. Not a GP appointment. Not waiting to see if it passes.
F — Face. Has their face fallen on one side? Can they smile?
A — Arms. Can they raise both arms and keep them there?
S — Speech. Is speech slurred or garbled? Can they understand you?
T — Time. If any of these are present, call emergency services now.
Two more worth knowing, sometimes added as BE-FAST: sudden loss of balance or coordination, and sudden change to vision in one or both eyes. Posterior-circulation strokes can present with dizziness, unsteadiness and visual disturbance and no facial droop at all, which is one reason they are more often missed.
Why the urgency is not an exaggeration
The treatments that restore blood flow work within a window measured from when symptoms began. Clot-busting drugs are generally given up to around four and a half hours from onset, and mechanical removal of a clot can be done considerably later in carefully selected patients — but in every case, earlier is better, and the commonly quoted estimate is that a large untreated stroke destroys something on the order of two million neurons a minute.
That is why the phrase is "time is brain" and why an ambulance rather than a car matters: the ambulance can alert the stroke unit before arrival, and it takes the patient to a hospital equipped to treat rather than the nearest one.
Four things to do, and three not to
Do: note the exact time symptoms started, or the last time the person was definitely normal — this single piece of information determines which treatments are available. Stay with them. Keep them comfortable and lying on their side if drowsy or vomiting. Have their medication list ready if you can.
Don't give aspirin. Don't give food or drink. Don't drive them yourself.
The aspirin point deserves explaining, because it is well-meant and it is wrong. Roughly 85% of strokes are ischaemic — a blocked vessel — and about 15% are haemorrhagic, a bleed. Aspirin is appropriate for the first and dangerous in the second, and you cannot tell which is which without a scan. That's what the first minutes in hospital are for.
If the symptoms go away, it is still an emergency
Symptoms that resolve on their own are a transient ischaemic attack, and it is the most under-treated warning in medicine. People feel fine afterwards and understandably conclude it was nothing.
The risk of a full stroke is highest in the days immediately following a TIA, and that risk is substantially reduced by rapid assessment and treatment. Current guidance is urgent specialist assessment — same day or within 24 hours, not next week. A TIA is a chance to prevent a stroke, and it expires quickly.
The ten risk factors
The INTERSTROKE study, across 32 countries, found that ten factors together account for roughly 90% of population-attributable stroke risk:
Hypertension · smoking · poor diet · abdominal obesity · physical inactivity · diabetes · heart disease · alcohol · high cholesterol · stress or depressive symptoms.
The first five alone account for about 80%.
It is worth pausing on how unusual that is. For most major diseases the modifiable share is a minority of the risk. Here it is the overwhelming majority — which makes stroke one of the most preventable catastrophic illnesses there is, and makes the fact that it remains the leading cause of neurological disability a failure of implementation rather than of knowledge.
Hypertension is the one that matters most
High blood pressure is associated with roughly a third of all stroke risk — by a distance the largest single modifiable factor.
It also has no symptoms. People do not feel high blood pressure, which is why it goes untreated for years, and why "get your blood pressure checked" is the most boring high-value health advice available.
It is the same factor sitting at the top of the dementia risk list. One measurement, taken seriously, sits underneath the two largest causes of neurological disability there are — and the vascular cluster that drives dementia risk is largely the same cluster listed above. Work on it once and you are working on both. The same vascular damage can also accumulate quietly as cognitive change rather than arriving as a single event, which is one reason memory worries are worth taking to a doctor rather than filing under ageing.
The one people miss: atrial fibrillation
An irregular heart rhythm substantially raises stroke risk, is often symptomless, and is treatable once found — anticoagulation reduces the risk considerably, which makes finding it genuinely high-value.
It can sometimes be picked up by feeling your own pulse for irregularity, and increasingly by consumer wearables. Those are not diagnostic, and they produce false alarms — but a device repeatedly flagging an irregular rhythm is worth taking to a doctor rather than dismissing, and an ECG settles it.
Two connected points. Untreated obstructive sleep apnea is associated both with atrial fibrillation and with stroke risk in its own right, and it is common and commonly undiagnosed. If you snore heavily and wake unrefreshed, that is a thread worth pulling.
Stroke in younger adults, and the migraine connection
Stroke is not only a disease of old age, and the causes in younger people are somewhat different: tearing of an artery in the neck (cervical artery dissection), which can follow relatively minor neck trauma; structural heart abnormalities such as a patent foramen ovale; and clotting disorders.
One combination is worth stating plainly because it affects a lot of people and is often not explained to them. Migraine with aura carries a modestly increased risk of ischaemic stroke, and that risk is amplified by combined hormonal contraception and by smoking. This is why prescribing guidance restricts the combined pill in women who have migraine with aura. If you have visual aura before your migraines and you are on a combined contraceptive, that is a specific conversation to have — not a reason to stop anything abruptly. Aura is described here, since a lot of people aren't sure whether what they get counts.
Where we sit
No supplement prevents stroke, including ours. The list of ten contains no supplements, and we're not going to imply that omega-3 belongs on it. The interventions that work are blood pressure control, smoking cessation, diet, movement, diabetes management, lipid management and treating atrial fibrillation — all of which happen at a GP surgery rather than a checkout.
This article is on our site because we're a brain company and stroke is the largest cause of brain injury there is. Writing only about the parts of the brain we sell things for would be a strange definition of covering the brain.
The two things worth doing this month
Know your blood pressure number. Know whether your pulse is regular.
Neither costs anything, most people know neither, and between them they cover the largest slice of a condition that is overwhelmingly preventable. Then learn FAST properly, and make sure the people you live with know it too — because in most strokes the person who calls the ambulance is not the patient.
Risk factor data from the INTERSTROKE case-control study. Treatment windows vary by health system and by individual circumstances, and the figures here are general rather than specific to any patient. This article is not medical advice. If you suspect a stroke, call emergency services immediately.