Do NOT use Lopressor if:

• you are allergic to any ingredient in Lopressor or to another beta-blocker (eg, propranolol)
• you have a very slow heart rate (eg, bradycardia), certain types of irregular heartbeat (eg, atrioventricular [AV] block, sick sinus syndrome), moderate to severe heart failure, very low systolic blood pressure (less than 100 mm Hg), or severe blood circulation problems
• you are taking mibefradil.

Contact your doctor or health care provider right away if any of these apply to you.

Some medical conditions may interact with Lopressor. Tell your doctor or pharmacist if you have any medical conditions, especially if any of the following apply to you:

• if you are pregnant, planning to become pregnant, or are breast-feeding
• if you are taking any prescription or nonprescription medicine, herbal preparation, or dietary supplement
• if you have allergies to medicines, foods, or other substances
• if you have an adrenal gland tumor (pheochromocytoma), have an overactive thyroid, or are scheduled to have surgery
• if you have low blood pressure or a history of heart attack, slow or irregular heartbeat, heart failure, or other heart problems; chest pain or angina; blood circulation problems; or liver problems
• if you have diabetes mellitus, chronic obstructive pulmonary disease (COPD), bronchitis, breathing problems, or a history of asthma.

Some medicines may interact with Lopressor. Tell your health care provider if you are taking any other medicines, especially any of the following:

• Amiodarone, bupropion, certain HIV protease inhibitors (eg, ritonavir), certain selective serotonin reuptake inhibitors (SSRIs) (eg, fluoxetine, paroxetine), cimetidine, digoxin, diphenhydramine, disopyramide, flecainide, hormonal contraceptives (eg, birth control pills), hydralazine, hydroxychloroquine, ketanserin, mefloquine, mibefradil, phenothiazines (eg, thioridazine), propafenone, quinazolines (eg, alfuzosin), quinidine, terbinafine, thiamines (eg, propylthiouracil), or verapamil because serious side effects such as very slow heart rate and very low blood pressure may occur
• Barbiturates (eg, phenobarbital), indomethacin, or phenylpropanolamine because they may decrease Lopressor's effectiveness
• Bupivacaine, disopyramide, flecainide, hydralazine, ketanserin, or lidocaine because the risk of their side effects may be increased by Lopressor
• Clonidine because stopping it or Lopressor suddenly can lead to a rapid increase in blood pressure.

This may not be a complete list of all interactions that may occur. Ask your health care provider if Lopressor may interact with other medicines that you take. Check with your health care provider before you start, stop, or change the dose of any medicine.

Important safety information:

• Lopressor may cause drowsiness, dizziness, or lightheadedness. These effects may be worse if you take it with alcohol or certain medicines. Use Lopressor with caution. Do not drive or perform other possible unsafe tasks until you know how you react to it.
• Lopressor may cause dizziness, lightheadedness, or fainting; alcohol, hot weather, exercise, or fever may increase these effects. To prevent them, sit up or stand slowly, especially in the morning. Sit or lie down at the first sign of any of these effects.
• Patients who take medicine for high blood pressure often feel tired or run down for a few weeks after starting treatment. Be sure to take your medicine even if you may not feel "normal." Tell your doctor if you develop any new symptoms.
• Do not suddenly stop using Lopressor without first talking your doctor. If your doctor decides you should no longer use Lopressor, you will need to stop Lopressor gradually according to your doctor's instructions.
• If your doctor has instructed you to check your blood pressure and heart rate regularly, be sure to do so.
• Do not take any medicines used to treat colds or congestion without first consulting with your doctor or pharmacist.
• Diabetes patients - Lopressor may hide signs of low blood sugar, such as rapid heartbeat. Be sure to watch for other signs or low blood sugar. Low blood sugar may make you anxious, sweaty, weak, dizzy, drowsy, or faint. It may also make your vision change; give you a headache, chills, or tremors; or make you more hungry. Check blood sugar levels closely. Ask your doctor before you change the dose of your diabetes medicine.
• Tell your doctor or dentist that you take Lopressor before you receive any medical or dental care, emergency care, or surgery.
• If you have a history of any severe allergic reaction, talk with your doctor. You may be at risk for an even more severe allergic reaction if you come into contact with the substance that caused your allergy. Some medicines used to treat severe allergies may also not work as well while you are using Lopressor.
• Lab tests, including liver and kidney function, blood pressure, and complete blood cell counts, may be performed while you use Lopressor. These tests may be used to monitor your condition or check for side effects. Be sure to keep all doctor and lab appointments.
• Lopressor should be used with extreme caution in children; safety and effectiveness in children have not been confirmed.
• Pregnancy and breast-feeding: If you become pregnant, contact your doctor. You will need to discuss the benefits and risks of using Lopressor while you are pregnant. Lopressor is found in breast milk. If you are or will be breast-feeding while you use Lopressor, check with your doctor. Discuss any possible risks to your baby.

All medicines may cause side effects, but many people have no, or minor, side effects.

Check with your doctor if any of these most common side effects persist or become bothersome:

Constipation; diarrhea; dizziness; dry mouth/eyes; gas; headache; heartburn; lightheadedness; mild drowsiness; muscle aches; nausea; pain, redness, or swelling at the injection site; stomach pain; trouble sleeping; unusual tiredness or weakness; vomiting.

Seek medical attention right away if any of these severe side effects occur:

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); blue or unusually cold hands or feet; chest pain; fainting; hallucinations; mood or mental changes (eg, confusion, depression); pounding in the chest; severe dizziness or lightheadedness; shortness of breath; slow or irregular heartbeat; swelling of the arms, hands, and feet; vision changes; wheezing; yellowing of the skin or eyes.

This is not a complete list of all side effects that may occur. If you have questions about side effects, contact your health care provider.