Metoprolol has been used for lowering high blood pressure for over 40 years and is still used for various heart conditions. This drug is not effective in treating high blood pressure in all patients, and it can cause side effects like low heart rate and loss of libido. Read on to learn more about the uses and potential side effects of Metoprolol.
NOTE: Selfhacked does not support taking or not taking this or any drug. We think drugs should only be tried as a last resort if needed and/or your doctor recommends it. Do not take this post as promoting the use of this medication. It’s for informational purposes alone. It’s a popular drug and people should know what it’s used for, the scientific evidence behind it, and its drawbacks.
What is Metoprolol?
Mechanism of Action
There are multiple types of adrenaline receptors. At normal doses, metoprolol blocks only one type, beta-1 adrenaline receptors. Activated beta-1 receptors raise blood pressure and heart rate, and increase the stress response [5, 6].
Metoprolol achieves its effects by preventing the activation of these receptors. Metoprolol reduces blood pressure by:
- Decreasing angiotensin II levels by decreasing aldosterone (a hormone that increases sodium in the kidneys) 
- Increasing flexibility of the aorta (main heart artery), which causes increased blood pressure when hardened 
- Strengthening small blood vessels (capillaries) in the heart, allowing for better blood flow 
Metoprolol may reduce heart damage after heart surgery, heart attack, and heart failure. Typically, the heart responds by “remodeling” the injured heart tissue in ways that increase the risk of future heart problems. Metoprolol reduces these remodeling processes by [10, 11]:
Metoprolol also fights inflammation and oxidation in the heart by:
- Lowering levels of the pro-inflammatory cytokines (IL-1β, CXCL1, and TNF-alpha). It also increased the anti-inflammatory cytokine IL-10 (in rats) [14, 15]
- Preventing neutrophils from moving to the heart 
- Lowering activity of NF-κB and vascular endothelial growth factor (VEGF), pro-inflammatory chemicals [12, 10]
- Reducing the number of macrophages in arterial plaques (in mice) 
- Increasing the number of glucocorticoid receptors, which respond to cortisol 
Uses of Metoprolol
1) Reduces High Blood Pressure
Metoprolol is taken in an extended-release (once daily) or an instant-release (twice daily) form. A DB-RCT of 195 patients with high blood pressure found that both forms reduced blood pressure and heart rate better than placebo following 6 weeks of treatment .
In a study of 100 patients (DB-RCT) with high blood pressure, metoprolol (instant-release and the extended-release) reduced blood pressure in 93% of patients after 8 weeks .
Metoprolol also improved heart function in elderly patients with high blood pressure and heart failure after 3 months of treatment, in a study of 330 people (open-label) .
2) Helps with Heart Failure
In a study of 3991 patients with congestive heart failure (DB-RCT), patients given metoprolol had higher chances of survival than the patients given placebo, after 1 year of treatment .
In another study of 383 patients with dilated cardiomyopathy, a major cause of heart failure, people treated with metoprolol reported increased levels of life satisfaction and physical activity after 18 months, compared to those given placebo .
Metoprolol may provide similar benefits for children with genetic heart conditions. A study (DB-RCT) of 30 children with heart failure due to inherited heart defects found that metoprolol improved heart function after 3 months of treatment .
Studies done in rats confirm these results. In rats with heart failure, metoprolol reduced the amount of damaged heart tissue and also decreased the irritation of the windpipe (trachea) that is often associated with heart failure [23, 24].
3) May Help Prevent Heart Attacks
A large meta-analysis (12 RCTs) with a total of over 61,000 patients that experienced a heart attack found that metoprolol reduced the chance of experiencing a second heart attack, but did not reduce the risk of death or of being rehospitalized .
Individual studies do suggest that metoprolol may reduce the risk of death following a heart attack. A DB-RCT of 1,395 patients given metoprolol or placebo after a heart attack found that metoprolol reduced the rate of death by 36%. It also reduced rapid heartbeat (ventricular fibrillation) and prevented further heart attacks in the first 3 months of treatment .
After a heart attack, an implant called a stent is sometimes placed in blood vessels of the heart to reopen them. In 1 study (RCT) of 270 patients, those who were given metoprolol within 6 hours of a heart attack and who then received a stent had less heart tissue death 1 week after the procedure .
Another study (DB-RCT) of 638 patients with heart stents failed to show a reduction in heart tissue death in patients given metoprolol .
4) Reduces Migraines
Metoprolol was recommended for the prevention of migraines in a report by the American Academy of Neurology and the American Headache Society .
5) May Reduce Arterial Plaques
In a study of 341 patients with clogged or blocked arteries (carotid arterial plaques), those given metoprolol for 3 years showed more signs of plaques breakdown than those given placebo .
A study in mice showed that metoprolol reduced the size of plaques in the heart as well .
6) Improves Heart Arrhythmia
Metoprolol is used to treat multiple types of heart arrhythmias, which are marked by an improper pattern or speed of heartbeats.
A study of 20 patients with inappropriate sinus tachycardia, a form of arrhythmia that causes excessive heart rate, found that metoprolol reduced resting heart rate from 114 to 93 beats per minute after 4 weeks. It also reduced heart rate during daily activity .
Rats given metoprolol after a severe heart attack had lower rates of several types of arrhythmias (including ventricular fibrillation, ventricular tachycardias, and premature ventricular contractions) than rats given a placebo .
Long-QT syndrome is a type of arrhythmia that is inherited genetically or caused by lifestyle factors like medications. In mice, metoprolol reduced the symptoms of long-QT syndrome caused by ziprasidone, an antipsychotic medication, and by amitriptyline, an antidepressant [34, 35].
Metoprolol may not be effective in treating the inherited form of long-QT syndrome, however. A study of 382 people with this form of the syndrome found that metoprolol is not as effective as 2 other beta-blockers (propranolol and nadolol) at preventing the recurrence of symptoms .
7) May Stabilize the Heart After Surgery
A pilot study of 215 patients found that people given metoprolol after heart surgery had a lower rate of dangerous arrhythmias (atrial fibrillation) than those given placebo .
In a study (RCT) of 8,351 people undergoing non-heart surgeries, patients given metoprolol before surgery who continued taking the drug for a month after surgery had a lower risk of having a heart attack than patients given a placebo. However, the risk of stroke and/or death was increased in the group given metoprolol .
Another study followed 599 patients undergoing blood vessel surgery and found that there was no difference in rates of heart attack, risk of dying, or of stroke between the group given metoprolol and the group given placebo .
8) May Help with Narrowed Heart Valves
Mitral valve stenosis is a narrowing of the heart’s mitral valve, which can block blood flow.
Two studies of mitral valve stenosis, one with 97 participants and another with 34, compared the effects of the drugs metoprolol and ivabradine. The study found that both drugs could reduce resting heart rate, and rate during exercise after 6 weeks of treatment [40, 41].
Metoprolol may also help in the treatment of aortic stenosis. One study (DB-RCT) of 40 people with asymptomatic aortic stenosis found that the muscles of the heart consumed less oxygen and operated more efficiently after taking metoprolol for 22 weeks .
9) Reduces Fainting
A study of 54 people showed that metoprolol prevented the recurrence of syncope (fainting) over one year of treatment .
Metoprolol may also be effective in treating loss of consciousness in children. In a study of 28 children, metoprolol worked as well as the conventional treatments (midodrine and ﬂudrocortisone) in preventing loss of consciousness over a year-long treatment period .
10) May Help with Traumatic Brain Injury
One study compared the outcomes of 356 patients with a traumatic brain injury admitted to the hospital over a 7-year period. Those patients given metoprolol after their injury had a lower risk of death than those who did not receive metoprolol .
11) May Help Heart Birth Defects
Fifteen patients with a specific type of heart birth defect, called Eisenmenger’s syndrome, showed improvement in their exercise capacity after 6 weeks of taking metoprolol. The initial results of this small study are promising, but it is worth noting that no control or placebo group was used .
12) May Help with Poor Circulation
Raynaud’s syndrome causes narrowing of the small blood vessels (usually in fingers and toes), leading to poor circulation.
One study of 46 patients with both hypertension and Raynaud’s syndrome found that metoprolol combined with felodipine (a calcium-ion channel blocker) improved blood circulation to the fingers and toes .
13) May Reduce Osteoporosis
Metoprolol promoted the growth and activity of bone cells in mice with low levels of estrogen, similar to that of postmenopausal women. This research suggests that women taking metoprolol for its other health effects may also benefit from its potential effect on bone growth .
14) May Help During Heart Attacks
Acute coronary syndrome happens when blood flow to the heart is suddenly cut off, such as during a heart attack.
15) May Be Used During Coronary Angiography
Metoprolol is often given to patients before an angiogram to achieve a low enough heart rate for the procedure. A study of 1,871 patients given metoprolol before having a coronary angiogram found that only 1 patient had a negative side effect due to metoprolol (temporary loss of consciousness) .
Another study of 662 patients that underwent coronary angiography found no evidence of adverse side effects in any of the cases where patients were given metoprolol to lower heart rate .
16) May Help with Chagas Disease
Chagas disease, caused by the parasite T. cruzi, can cause heart failure, altered heart rate, sudden death (cardiac arrest), and stroke .
In a study of 9 patients, metoprolol reduced symptoms of congestive heart failure due to Chagas disease, including rapid heartbeat and reduced pumping volume, after 10 weeks of treatment .
Metoprolol also reduced abnormal heart activity due to Chagas disease in rats .
Safety & Side Effects
The most commonly reported side effects include:
- Difficulty sleeping 
- Erectile dysfunction (in men) [62, 63, 64, 65]
- Sexual dysfunction (in women) [66, 67]
- Abnormally slow heart rate (bradycardia) 
Other potential side effects of metoprolol are:
- Increased insulin resistance (in people with diabetes) [69, 70]
- Increase in symptoms of depression and burnout (in people with previously diagnosed psychological disorders) 
- Increased triglyceride levels 
- Psychosis or delirium, especially in older patients [73, 74]
- Psoriasis [75, 76]
- Sleepwalking [77, 78]
- Hallucinations and vivid dreams 
- Lichenoid dermatitis 
- Erythema multiforme 
Limitations and Caveats
The effectiveness of metoprolol can vary widely, and may be based on a person’s genetic makeup. African-American patients, in particular, are less likely to respond to treatment with metoprolol for heart conditions [82, 9].
Metoprolol may lower the heart rates of women more than it does for men, suggesting that women may require smaller doses .
Many of the uses of metoprolol have only been studied in a small number of patients, including its potential benefits for vasovagal syncope, Raynaud’s syndrome, Eisenmenger’s syndrome, and Chagas disease. Larger studies are needed to confirm the effects of metoprolol on these conditions [43, 53, 47, 46].
In the case of postmenopausal osteoporosis, only studies using mice have been done and follow-up studies using humans are needed .
Metoprolol should be taken with caution during pregnancy. It does not appear to present a large risk during pregnancy, but it can have effects on newborn infants, including low blood sugar and slowed heartbeat .
Pregnancy can change the way the body breaks down metoprolol. Late in pregnancy, women may break down metoprolol more quickly, becoming less responsive to the drug .
It is likely safe to breastfeed while taking metoprolol at low doses, however .
Some medications prevent cytochrome P450-2D6, the enzyme that breaks down metoprolol, from functioning properly. This can result in abnormally high levels of metoprolol in the body, which may be toxic. Medications with a confirmed interaction of this type include:
- Vorinostat (suberoylanilide hydroxamic acid), used to treat cutaneous T-cell lymphoma 
- Imatinib, which treats various types of cancer 
- Paroxetine, fluoxetine, and bupropion, all used as antidepressants [89, 90, 91]
- Mirabegron, which treats overactive bladder 
- Ellagic acid and gallic acid, antioxidant supplements 
- Terbinafine, which treats fungal infections 
Other medications reduce the ability of the gut to absorb metoprolol. These include :
- Diphenhydramine (antihistamine, found in Benadryl)
- Procainamide and quinidine (medications for heart arrhythmia)
- Bisoprolol (treats high blood pressure or heart failure)
Metoprolol may lower the amount of metformin (a medication given for type 2 diabetes and for polycystic ovary syndrome) in the blood. Taking metoprolol and metformin may also result in higher levels of uric acid, which is associated with kidney damage [96, 97].
When used together, metoprolol and angiotensin-converting enzyme inhibitors, commonly used to treat hypertension or heart failure, may increase allergic reactions .
Metoprolol Compared to Other Drugs
A study of 183 patients found that bisoprolol was more effective than metoprolol in reducing heart rate, but the 2 drugs were similar in their ability to reduce blood pressure .
A study of 60 people with mild high blood pressure compared the effects of metoprolol and nebivolol and determined that metoprolol and nebivolol had similar effects. Both reduced blood pressure during exercise and while resting, after 8 weeks of treatment .
Metoprolol and carvedilol were compared in a DB-RCT of 3,029 patients, which showed that carvedilol was better than metoprolol at preventing death in people with chronic heart failure over 5 years. These findings have been questioned, however, because of the doses and form of metoprolol used. Thus, more research is needed to confirm these results .
Metoprolol With Other Drugs
Metoprolol may also be used in combination with other medication to lower blood pressure. One RCT of 1,092 patients showed that a combination of metoprolol and felodipine lowered blood pressure more effectively than either drug alone after 9 weeks, but at lower doses and with fewer side effects [103, 104].
When taken as a pill to treat high blood pressure, 100 to 200 mg of metoprolol is standard once a day in an extended-release form, or patients may take 50 to 100 mg twice a day in an instant-release form. Both forms are equally effective, but the extended-release version may give a more stable effect, and may better control heart rate during exercise [19, 106, 107, 108, 109].
Metoprolol is only effective in treating high blood pressure in about 50 to 60% of people. Genetic differences in patients are the main reasons that some people respond to metoprolol while others do not. Although several genes accounting for this have been found, much of this variation in responsiveness has not yet been explained [112, 113].
Cytochrome P450 2D6 (CYP2D6) is the enzyme that breaks down metoprolol in the body. This gene has many different forms in humans that result in metoprolol being either quickly broken down and removed from the blood or being broken down more slowly. The fast-acting forms metabolize up to 36x more metoprolol than the slower forms [114, 115, 116].
People who break metoprolol down slowly, due to their slow-acting version of the CYP2D6 enzyme, are more likely to respond to metoprolol treatment. They show larger reductions in blood pressure and heart rate than people who break down metoprolol quickly [117, 118].
Metoprolol functions by activating type 1 beta adrenaline receptors. People with a certain form of the type 1 beta adrenaline receptor gene may need lower doses of metoprolol to lower blood pressure. A study of 29 men taking metoprolol showed that men with this form of the gene had lower levels of active renin, an enzyme produced by the kidneys that reduces blood pressure .
Angiotensin-converting enzyme produces angiotensin II, a molecule that activates the “fight or flight” response activity. Metoprolol works in part by reducing levels of angiotensin II .
Multiple forms of gene coding for this enzyme exist in humans, and this may impact how a person reacts to metoprolol. One form of the gene results in lower angiotensin II levels. People with this version had a larger decrease in heart rate after taking metoprolol for 8 weeks, in a study of 96 Han Chinese patients with high blood pressure .
One user said that metoprolol controls their blood pressure with mild side effects, such as dry mouth and dizziness that went away after a few days.
One user was prescribed instant release metoprolol to lower heart rate. It decreased their heart rate from 110 to around 75. They started taking the extended-release formulation recently, and comment that it works well during the whole day. Metoprolol had little to no effect on their blood pressure though.
Another user had been taking metoprolol for around 2 years. It helped them a lot, but they experienced tiredness almost daily. It did help them get rid of rapid heart beating and migraines.
One user reported skin breakouts from Metoprolol, but success with reducing migraines and fast heartbeat.
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