Metoprolol

Is metoprolol safe?

Yes, when it is taken as prescribed and not stopped abruptly. Metoprolol has been sold in the US since 1978, and in people with weak hearts it does more than lower blood pressure: in the MERIT-HF trial of 3,991 people with heart failure, 145 died on Toprol-XL against 217 on placebo, a 34% lower risk. We score it 74, below amlodipine and lisinopril, because a slow heart, overdose and abrupt stopping carry real risks.

Metoprolol comes in two forms. Metoprolol tartrate (Lopressor) is immediate release; the US label starts at 100 mg a day for high blood pressure, in one or two doses, with an effective range of 100 mg to 450 mg. Metoprolol succinate (Toprol-XL, Kapspargo Sprinkle) is extended release and taken once a day; for blood pressure it starts at 25 mg to 100 mg, and for heart failure at 12.5 mg or 25 mg, doubled every two weeks up to 200 mg as tolerated.

What happens if you stop metoprolol suddenly?

This is the warning most people have heard of. Beta-blockers dampen the effect of adrenaline on the heart, and the body adapts. When they are stopped suddenly, angina can get worse, and some people have had heart attacks. The label advises reducing the dose over 1 to 2 weeks with monitoring, and warns patients not to interrupt treatment without their doctor's advice. Because coronary disease is common and often silent, it gives the same advice to people who take metoprolol only for blood pressure. The NHS puts it simply: stopping suddenly can make your condition worse.

For years this sat in a boxed warningBoxed warningThe strongest safety warning the US FDA puts on a medicine's label, printed inside a black border at the top.More in the glossary. In January 2022 the FDA approved a revised Toprol-XL label that removed the box, added a separate warning on slow heart rate, and kept the abrupt-stopping text as the first item in Warnings and Precautions. The advice did not change; only its format did. Some generic and repackaged labels still show the old box.

Running out of tablets is the common real-world cause, so it pays to reorder early, take enough on holiday and tell any hospital team that you take a beta-blocker.

Side effects and who should be careful

The common side effects follow from what the drug does: tiredness, dizziness, a slow pulse, cold hands and feet, and sometimes low mood, diarrhoea or shortness of breath. Most are mild. In MERIT-HF, 10.3% of people on Toprol-XL stopped it for side effects, slightly fewer than the 12.2% on placebo.

The label's serious warnings cover specific groups:

• Heart rhythm problems. Slow heart rate, sinus pauses, heart block and cardiac arrest have occurred. Metoprolol is contraindicatedContraindicationA situation in which a medicine should not be used, because the risk clearly outweighs any benefit, such as a known allergy to it.More in the glossary in severe bradycardia, second- or third-degree heart block without a pacemaker, and cardiogenic shock.
• Heart failure. It can briefly worsen symptoms while the dose is being raised, which is why doctors increase it slowly.
• Asthma and COPD. The label says people with bronchospastic disease should in general avoid beta-blockers.
• Diabetes. It can mask the racing heart that warns of low blood sugar.
• Severe allergies. People on beta-blockers may not respond to usual doses of adrenaline (epinephrine) during anaphylaxis.
• Surgery. In a trial of 8,351 people having non-cardiac surgery, starting high-dose metoprolol hours before the operation raised the rate of stroke (1.0% vs 0.5%) and death (3.1% vs 2.3%). The label warns against starting it this way, but also against routinely stopping long-term beta-blockers before surgery.

Interactions to know

Metoprolol is broken down by the liver enzyme CYP2D6CYP450 enzymesA family of liver enzymes that break down many medicines. When another drug or supplement speeds them up or slows them down, drug levels change.More in the glossary. Strong blockers of that enzyme, including the antidepressants fluoxetine and paroxetine, quinidine and propafenone, can double metoprolol levels and make it less selective for the heart. Verapamil, diltiazem, digoxin and clonidine all slow the heart further. Clonidine also needs a set order when stopping: the label says metoprolol should be withdrawn several days before clonidine is tapered, to avoid a dangerous rebound in blood pressure.

Overdose

A metoprolol overdose can cause a very slow pulse, collapse in blood pressure, heart block, wheezing and coma. The label notes that beta-blocker poisoning can resist the usual drugs used for resuscitation, and dialysis is unlikely to help. Anyone who has taken more than prescribed should call 111 in the UK, Poison Control on 1-800-222-1222 in the US, or emergency services if they feel faint or breathless.

How we scored it

Track record (95) and dependence (85) are strong; the dependence score is not perfect because of the rebound risk on stopping. Regulatory warnings (75) reflect a removed boxed warningBoxed warningThe strongest safety warning the US FDA puts on a medicine's label, printed inside a black border at the top.More in the glossary and recent lot recalls. Serious side effects (74), interactions (65) and overdose marginOverdose marginHow far a normal dose is from a harmful one. A wide margin means an accidental extra dose is unlikely to cause serious harm.More in the glossary (60) are the weaker factors. A lower score is not a reason to stop metoprolol: talk to your doctor or pharmacist if you have concerns.