Side Effects of Metoprolol and Atenolol
Both metoprolol and atenolol share common beta-blocker side effects including hypotension, bradycardia, and bronchospasm, but metoprolol causes significantly more central nervous system effects—particularly sleep disturbances, vivid dreams, and fatigue—due to its lipophilic properties that allow greater brain penetration. 1, 2, 3
Common Side Effects (Both Drugs)
Cardiovascular Effects
- Hypotension (systolic BP <90 mmHg): occurs in approximately 25-27% of patients 4, 5
- Bradycardia (heart rate <40 bpm): affects 3-16% of patients 1, 2, 3
- Cold extremities and peripheral arterial insufficiency (Raynaud-type): approximately 12% with atenolol 5
- Heart block (second or third degree): 4-5% of patients 1, 3
- Worsening heart failure: particularly in patients with pre-existing ventricular dysfunction 2
Respiratory Effects
- Bronchospasm and wheezing: approximately 1-3% of patients 1, 3, 4
- Dyspnea: reported in 3-6% of patients 4, 5
These respiratory effects are particularly concerning in patients with reactive airway disease or asthma, where both drugs should be used with extreme caution or avoided entirely 1, 2, 3.
Gastrointestinal Effects
- Diarrhea: approximately 3-5% of patients 4, 5
- Nausea: 3-4% of patients 4, 5
- Dry mouth, gastric pain, constipation: approximately 1% each 4
Critical Differences: CNS Side Effects
Metoprolol (Lipophilic)
Metoprolol causes substantially more CNS-related adverse effects because it crosses the blood-brain barrier readily. The most problematic effects include:
- Sleep disturbances: significantly increased awakenings (7.2 ± 4.7 vs 3.9 ± 2.7 with placebo) and time awake (19.5 ± 24.3 minutes vs 9.2 ± 7.5 minutes) 6
- Vivid and disturbing dreams: common complaint across multiple studies 7, 8, 9
- Fatigue and tiredness: reported in approximately 26% of patients 5, 7
- Depression: approximately 12% of patients 5
- Dizziness and lethargy: 13% and 3% respectively 5
- Mental confusion and short-term memory loss: documented but less common 4
- Sexual dysfunction: failure to achieve satisfactory intercourse reported significantly more than with atenolol 8
Atenolol (Hydrophilic)
Atenolol produces minimal CNS effects because it does not readily cross the blood-brain barrier. Studies consistently show:
- Significantly fewer sleep disturbances compared to metoprolol: fewer awakenings (3.6 ± 2.9) and less time awake (10.2 ± 11.6 minutes) 6
- No significant CNS side effects when patients switched from lipophilic beta-blockers to atenolol 8, 9
- Tiredness: 26% vs 13% placebo, though this may not be drug-specific 5
- Depression: 12% vs 9% placebo 5
The landmark crossover studies demonstrate that discontinuing lipophilic beta-blockers and switching to atenolol produced significant improvement in sleep quality, dreams, concentration, memory, energy, and anxiety 8, 9. When metoprolol was introduced, patients experienced significant increases in sleep disturbance (p<0.01) and restless nights (p<0.05) compared to atenolol 8.
Additional Considerations
Depression Risk
Long-term beta-blocker therapy may confer clinical risks including depression, fatigue, and reduced libido 10. This effect appears more pronounced with lipophilic agents like metoprolol. Calcium channel blockers (verapamil, diltiazem) cause less depression and may be preferred alternatives when CNS effects are problematic 10.
Renal Function Impact
Atenolol elimination depends on kidney function and requires dose reduction in severe renal dysfunction (GFR <30 mL/min), while metoprolol does not 1, 3, 11. However, contrary to expectations, atenolol was associated with lower 90-day mortality compared to metoprolol regardless of kidney function (0.97% vs 1.44%; relative risk 0.68) 12.
Other Notable Side Effects
- Peyronie's disease: rare (<1 in 100,000) 4
- Reversible alopecia: very rare 4
- Psoriasis exacerbation: reported with both drugs 4, 5
- Hepatic dysfunction: very rare reports of hepatitis and transaminase elevations with metoprolol 4
Clinical Pitfalls to Avoid
Do not abruptly discontinue either drug: Sudden cessation increases risk of cardiovascular morbidity and mortality, particularly post-operatively (mortality 50% vs 1.5% with continuation) 13
Avoid in decompensated heart failure: Both drugs are contraindicated in acute decompensated systolic heart failure, though they are beneficial once compensated 1, 2, 3
Exercise caution with AV block: Contraindicated with second or third-degree AV block without a pacemaker 1, 2, 3
Monitor elderly patients closely: CNS side effects are particularly problematic in older adults, who may experience confusion, delirium, and gait disturbances with metoprolol 14
Consider lipophilicity when CNS symptoms emerge: If patients develop sleep disturbances, vivid dreams, or depression on metoprolol, switching to atenolol typically resolves these symptoms 8, 9