Can I smoke or drink water before a blood test?


Can I smoke before a blood test?

Smoking before a blood test can affect the results, as it influences various biomarkers and bodily functions. Dr. Christos Zavos, a board-certified gastroenterologist and hepatologist, advises against smoking prior to a blood test for several reasons:

  1. Impact on Blood Pressure: Smoking can temporarily raise blood pressure due to the nicotine content, which may not provide an accurate assessment of your baseline blood pressure levels.
  2. Effect on Heart Rate: Nicotine also stimulates the heart, leading to an increased heart rate, which can affect tests that require a normal resting heart rate.
  3. Influence on Blood Sugar Levels: Smoking can cause a short-term rise in blood sugar levels, which is particularly significant if you are being tested for diabetes or blood glucose levels.
  4. Alteration of Blood Lipid Levels: Smoking can affect cholesterol and triglyceride levels, potentially leading to misleading lipid panel results.
  5. Interference with Oxygen and Carbon Monoxide Levels: Smoking increases carbon monoxide in the blood, which decreases oxygen levels. This can impact tests related to pulmonary function and cardiovascular health.

For the most accurate results, it is recommended to avoid smoking for at least 12 hours before undergoing a blood test. If you have specific questions regarding how smoking may impact your blood test or if you need personalized advice related to smoking cessation and its benefits for gastrointestinal and liver health, you are encouraged to contact Dr. Zavos directly. He is available through the contact form on, by phone at (+30)-6976596988 and (+30)-2311283833, or by email at

Can I drink water before a blood test?

Yes, you can generally drink water before a blood test. In fact, staying hydrated by drinking water can make it easier to draw blood by helping to keep your veins full and pliable. Dr. Christos Zavos, a board-certified gastroenterologist and hepatologist, recommends drinking water prior to a blood test unless otherwise directed by your healthcare provider.

Considerations for Different Types of Blood Tests

  • Fasting Blood Tests: For tests that require fasting, such as a fasting blood glucose test or a lipid profile, you should avoid eating or drinking anything other than water for 8 to 12 hours before the test. Water does not affect the results of these tests and is encouraged to prevent dehydration.
  • Non-fasting Blood Tests: For blood tests that do not require fasting, water can be consumed normally.
  • Other Tests: If you are undergoing a specific test that has unique requirements, it’s always best to follow the instructions provided by your healthcare provider.

Drinking water before a blood test is generally beneficial and can help make the blood collection process smoother and more comfortable.

Last update: 14 April 2024, 02:50


Gastroenterologist - Hepatologist, Thessaloniki

PhD at Medical School, Aristotle University of Thessaloniki, Greece

PGDip at Universitair Medisch Centrum Utrecht, The Netherlands

Ex President, Hellenic H. pylori & Microbiota Study Group