What Are the Warning Signs of a Stroke, and Why Does Time Matter?

The warning signs of a stroke are sudden changes: a drooping face, weakness or numbness in an arm or leg, slurred or confused speech, trouble seeing, loss of balance, or an abrupt severe headache. Time matters because a stroke can keep injuring brain tissue while it continues, and some treatments can only be given in a limited treatment window that the emergency team determines. This article explains each sign, what to do, and which symptoms need 911.

What are the warning signs of a stroke?

A stroke happens when blood flow to part of the brain is blocked or when a blood vessel in or around the brain bleeds. MedlinePlus (NIH) describes the typical warning signs as coming on suddenly. That sudden onset is the feature that matters most.

Common warning signs include:

• Face: one side of the face droops or feels numb. A smile may look uneven.
• Arm or leg: weakness or numbness, often on one side of the body. One arm may drift downward when both are raised.
• Speech: slurred words, trouble finding words, or trouble understanding what others say. Some people seem confused for no clear reason.
• Vision: blurred or lost vision in one or both eyes, or double vision.
• Balance and walking: sudden dizziness, loss of coordination, or trouble walking.
• Headache: a sudden, severe headache that feels unlike your usual headaches. This can be associated with bleeding in or around the brain.

Not everyone has every sign. A stroke can involve just one of them, and the pattern depends on which part of the brain is affected. Pain is often absent, which is one reason people wait to see if the problem passes.

A quick check: face, arm, speech, time

Many emergency programs teach the FAST check because it is easy to remember when you are frightened:

• F, Face: ask the person to smile. Does one side droop?
• A, Arm: ask them to raise both arms. Does one drift down or feel weak?
• S, Speech: ask them to repeat a simple sentence. Is it slurred, strange or hard to say?
• T, Time: if you see any of these, call 911 and note when the symptoms started, or when the person was last known to be well.

FAST does not catch every stroke. Sudden vision loss, sudden loss of balance, and a sudden severe headache can occur without a drooping face or arm weakness. If something feels abruptly wrong with the body or thinking, treat it as an emergency even if the FAST check looks normal. Only clinicians can decide whether a stroke is the cause, and they do that with an examination and brain imaging.

Why does time matter in a stroke?

Brain cells depend on a steady supply of oxygen-rich blood. When that supply is cut off, brain tissue can be injured as the stroke continues. Reviews describing stroke as an emergency condition, such as this paper on reconceptualising stroke as an emergency condition, make the same point that this article does: the faster a stroke is recognized and treated, the more brain function may be protected.

Several things make speed important:

• Treatment depends on the type of stroke. A clot-related stroke and a bleeding stroke need very different care. Emergency imaging is how clinicians tell them apart, and the wrong treatment for one type can cause harm in the other.
• Clot-related strokes have a limited treatment window. Clot-busting medicine (tissue plasminogen activator, or tPA) is used for some ischemic strokes, and expert consensus statements such as this consensus on intravenous tPA for acute ischemic stroke describe that it is suitable only for carefully selected patients. Emergency teams decide eligibility, and the start time of symptoms is a key piece of information they need. Some patients may also be treated with procedures that remove a clot.
• Calling 911 starts care early. Emergency medical crews can alert the hospital before you arrive, so the stroke team and imaging can be ready.

Knowing when symptoms began is valuable. If you woke up with symptoms, tell the team the last time you were known to be well. Do not guess or round the time, because the team uses it to decide which treatments are safe.

Two main kinds of stroke

Ischemic stroke happens when a clot or narrowing blocks blood flow to the brain. Fatty buildup in artery walls (atherosclerosis) can contribute, and so can clots that form elsewhere, such as in the heart during an irregular heart rhythm. Several factors contribute, and the cause is not always found.

Hemorrhagic stroke happens when a blood vessel in or around the brain breaks and bleeds. High blood pressure and weak spots in blood vessels are among the contributors. A sudden, severe headache, vomiting, or a rapid drop in alertness can accompany a bleed, though these signs can also occur in other conditions.

You cannot tell the type from symptoms alone, even as a clinician. That is why the advice is the same for everyone: call 911 and let the hospital sort it out.

Symptoms that come and go

A transient ischemic attack (TIA), sometimes called a mini-stroke, causes stroke-like symptoms that go away. MedlinePlus (NIH) explains that a TIA is a warning that a full stroke may follow in some people, and that it should be treated as an emergency even if the symptoms resolve.

It is tempting to think "it passed, so I am fine." Clinicians cannot tell from the symptoms alone whether a TIA is a single event or the first of a larger problem, so an urgent evaluation looks for the cause and for ways to lower the chance of a stroke. Brief episodes of vision loss in one eye, a short spell of slurred speech, or a few minutes of arm weakness all deserve an emergency visit.

What to do while you wait for help

If you think you or someone near you is having a stroke:

• Call 911. Do not wait to see if it gets better, and do not drive yourself or the person to the hospital. Paramedics can begin care and alert the hospital.
• Note the time. Write down when symptoms started or when the person was last known to be well.
• Keep the person calm and still. Have them sit or lie in a comfortable position. If they are drowsy or vomiting, the 911 dispatcher can tell you how to position them.
• Do not give food, drink or pills. Swallowing can be unsafe during a stroke. Do not give aspirin or other medicine unless the 911 dispatcher or an emergency clinician tells you to, because the right choice depends on the type of stroke.
• Gather information. Have a list of medicines, especially blood thinners, and any known conditions ready for the crew.

If the person becomes unresponsive and is not breathing normally, tell the dispatcher so they can guide you through CPR.

Conditions that can look like a stroke

Some conditions can imitate stroke symptoms, including low blood sugar, a seizure, a migraine with aura, and some infections. Migraine aura can cause vision changes, numbness or speech trouble, and it is covered in our article on telling migraine from something more serious. The point for stroke is simple: you do not have to figure out the cause. If the symptoms are sudden and new, or unlike anything you have had before, the emergency team can check for stroke and for the look-alikes. A mistaken alarm costs far less than a missed stroke.

Stroke signs should be taken as a stroke first even when another cause such as low blood sugar is possible. If you have diabetes and are checking your sugar, do so while the call is being made, not instead of it.

Who is at higher risk?

Anyone can have a stroke, including younger adults and people who feel healthy. Factors associated with higher risk include:

• High blood pressure. It often causes no symptoms. Our article on the silent signs of high blood pressure covers this, and MedlinePlus (NIH) lists ways to help prevent it.
• Atrial fibrillation. This irregular heart rhythm can allow clots to form in the heart. Our atrial fibrillation article explains it in detail.
• Atherosclerosis. Narrowing of arteries from fatty buildup can reduce blood flow to the brain.
• Diabetes, smoking, high cholesterol, and a previous stroke or TIA.
• Family history and age. Risk generally rises with age.

Having a risk factor does not mean a stroke will happen, and having none does not rule one out. Your clinician can look at your overall picture and decide which checks and treatments make sense for you. If you take a blood pressure or blood-thinning medicine, ask your prescriber or pharmacist before changing how you take it, and read the label cautions.

After the emergency: recovery

Stroke recovery varies widely. Some people recover much of their function, while others have lasting changes in movement, speech, thinking or mood. Stroke rehabilitation may include physical, occupational and speech therapy, and it often begins in the hospital. Ask the care team what to expect for your situation, because outcomes depend on the area of the brain affected, the type of stroke and how quickly care started.

Feeling low, anxious or exhausted after a stroke is common, and it is worth telling your clinician. If thoughts of harming yourself ever appear, call or text 988, the Suicide and Crisis Lifeline.

When to Seek Medical Care