Before you begin using a medication, be sure to inform your doctor of any medical conditions or Allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use Tenormin (Atenolol).

Breathing conditions: In general, people who have Asthma and certain other breathing problems or chronic lung disease should avoid taking a beta-blocker such as Tenormin (Atenolol), as it can cause breathing difficulty. Low doses of Tenormin (Atenolol) may be taken with caution by people with asthma who do not respond to or cannot tolerate alternative treatment. If you have breathing problems, discuss with your doctor how Tenormin (Atenolol) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Tenormin (Atenolol), and whether any special monitoring is needed.

Drowsiness/reduced alertness: The use of Tenormin (Atenolol) is unlikely to impair your ability to drive or operate machinery. However, it should be taken into account that dizziness, fatigue, or a slower reaction time may occur.

History of heart failure: Beta-blockers, such as Tenormin (Atenolol), can worsen existing heart failure. It is important to take Tenormin (Atenolol) exactly as prescribed by your doctor to decrease the chance of this happening. If you have a history of heart disease, discuss with your doctor how Tenormin (Atenolol) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Tenormin (Atenolol), and whether any special monitoring is needed.

Hyperthyroidism: If you have hyperthyroidism (high levels of Thyroid hormones) you should use caution while taking Tenormin (Atenolol), as it may reduce the symptoms of this condition, giving a false impression of improvement. Stopping the medication suddenly could worsen this condition.

Kidney Disease: The kidneys are partially responsible for removing Tenormin (Atenolol) from your body. Kidney disease or reduced kidney function may cause Tenormin (Atenolol) to build up in the body, causing side effects. If you have reduced kidney function or kidney disease, discuss with your doctor how Tenormin (Atenolol) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Tenormin (Atenolol), and whether any special monitoring is needed.

Low blood sugar: The signs of low blood sugar may not be as noticeable when taking Tenormin (Atenolol). If you have Diabetes and take insulin or other medications that affect insulin levels in the blood, discuss with your doctor how Tenormin (Atenolol) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Tenormin (Atenolol), and whether any special monitoring is needed. Your doctor will monitor you while you are taking Tenormin (Atenolol) and may need to adjust the doses of diabetes medications.

Prinzmetal's angina: Tenormin (Atenolol) may increase the number and duration of angina attacks in patients with Prinzmetal's angina. If you have this condition, be cautious while taking Tenormin (Atenolol). Report unusual chest pain to your doctor as soon as possible.

Severe allergies: If you have allergies severe enough to cause Anaphylaxis (severe allergic reaction) (a severe allergic reaction where swelling of the face, lips, and throat make it difficult to breathe), you should talk to your doctor about what to do if you have an allergic reaction. Tenormin (Atenolol) may make it more difficult to treat your allergic reaction with Epinephrine.

Slow heart rate: In general, people with an abnormally slow pulse should not take a beta-blocker such as Tenormin (Atenolol).

Stopping usage: Tenormin (Atenolol) should not be stopped suddenly. There have been reports of severe worsening of angina and of Heart Attack or abnormal heart rhythms occurring in people with angina pectoris who have done this. If Tenormin (Atenolol) needs to be stopped, it should be done gradually under supervision of your doctor.

Surgery: If you are scheduled for surgery, inform all doctors involved in your care that you are taking Tenormin (Atenolol).

Pregnancy: Studies have shown that Tenormin (Atenolol) does cross the placenta and there have been reports of harm to the developing baby if Tenormin (Atenolol) is taken by the mother during pregnancy. Tenormin (Atenolol) should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking Tenormin (Atenolol), contact your doctor immediately.

Breast-feeding: Tenormin (Atenolol) passes into breast milk. If you are a breast-feeding mother and are taking Tenormin (Atenolol), it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using Tenormin (Atenolol) have not been established for children.