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Why do I feel dizzy after donating blood?

It’s quite common to feel lightheaded or dizzy after giving blood. This happens because donating blood causes a temporary drop in blood pressure and reduction in the number of red blood cells that carry oxygen throughout your body.

The symptoms are usually mild and last only for a few minutes or hours. Knowing what causes dizziness after blood donation and how to minimize it can help you have a better donation experience.

What causes dizziness after donating blood?

When you donate blood, about 1 pint (500 ml) is removed. This causes an immediate drop in blood volume, blood pressure and red blood cells that’s large enough to make some people feel temporarily dizzy or lightheaded.

Specifically, donating blood leads to:

  • Drop in blood volume – Removing a significant amount of blood decreases the overall volume of blood in your body. This directly lowers blood pressure.
  • Reduced red blood cells – Blood donation reduces the number of red blood cells that transport oxygen throughout your body. The temporary lack of oxygen can lead to dizziness.
  • Fluid shifts – As your body works to replenish the lost blood volume, fluids shift between your blood vessels and tissues. These shifts can alter blood pressure and circulation.

The dramatic yet temporary reduction in blood volume and red blood cells reduces the amount of oxygen delivered to your brain, causing you to feel lightheaded or dizzy.

Who is more likely to experience dizziness?

Most blood donors feel fine after giving blood. But some are more prone to dizziness, lightheadedness and fainting, including:

  • Young adults – Dizziness is most common in younger adults under the age of 30. The bodies of younger blood donors replenish blood volume differently than older adults.
  • First-time donors – Donating blood for the first time can increase nerves and anxiety, which may increase the risk of feeling lightheaded or faint.
  • Smaller body size – People who weigh less have less circulating blood volume. Removing 1 pint has a greater relative impact on blood pressure.
  • Women – Fainting after blood donation occurs more often in younger women than men.
  • People prone to low blood pressure – Those with chronically low blood pressure are more likely to experience dizziness when blood volume drops further.

However, anyone can feel dizzy or faint after giving blood, regardless of age, gender, size or experience donating.

How long does dizziness last after donating blood?

Feeling lightheaded or dizzy after blood donation is temporary. Symptoms usually begin shortly after giving blood but improve quickly:

  • Immediately after donation – Dizziness is most common within the first 15 minutes after blood collection while your blood pressure is lowest.
  • 2 hours post-donation – Most people’s blood pressure and oxygen levels normalize within a few hours. Any dizziness or lightheadedness usually resolves within this time frame.
  • Rare after 24 hours – Lingering symptoms that last longer than 24 hours are very rare. This could indicate complications like anemia and should be evaluated by a doctor.

If you have low blood pressure, are prone to dizziness or faint easily, you may take a bit longer to recover after blood donation. But dizziness shouldn’t persist for more than a day.

How to minimize dizziness when donating blood

You can take steps before, during and after donation to minimize temporary dizziness:

Before donation

  • Eat iron-rich foods – Boost iron intake from meat, beans, spinach and fortified cereals to build new red blood cells.
  • Hydrate well – Drink extra fluids so your blood volume is optimized.
  • Get adequate sleep.
  • Avoid alcohol for 24-48 hours.

During donation

  • Stay calm and relaxed.
  • Don’t look directly at the needle or blood.
  • Talk to staff if you feel faint – They can help you stop the donation.
  • Take slow deep breaths.

After donation

  • Have a snack and drink – Replenish fluids, calories, salt and minerals right after donating.
  • Rest for 15 minutes – Don’t rush off immediately.
  • Change posture slowly – Make transitions between lying/sitting/standing gradually.
  • Avoid strenuous physical activity – Take it easy for the rest of the day.

When to see a doctor

In most cases, dizziness resolves within a few minutes to hours after blood donation. Seek medical care if you experience:

  • Fainting or loss of consciousness
  • Symptoms lasting more than 24 hours
  • Confusion, blurry vision or loss of balance
  • Headaches, fatigue or rapid heart rate that persists

These could be signs of complications like anemia, dehydration, abnormal heart rhythms or orthostatic hypotension. Let the blood donation staff know if you have any concerns after leaving the blood drive.


Feeling lightheaded, weak or dizzy after giving blood is very common and expected due to the temporary loss of blood volume, red blood cells and drop in blood pressure. Stay well hydrated, minimize activity and move slowly when getting up to help avoid significant dizziness. If symptoms don’t resolve within 24 hours, be sure to follow up with a doctor to rule out potential complications of blood donation.