According to the Centers for Disease Control and Prevention (CDC), almost half the population of the United States has hypertension, otherwise known as high blood pressure. Yet as commonplace as it is, only about a quarter of those affected by high blood pressure are actively managing it with prescription drugs. Some of this may be due to the perception that blood pressure medication comes with certain unwanted side effects. Metoprolol is an example of a class of blood pressure medications called beta blockers that is known to have side effects, and one of those side effects some people report is weight gain.
What Is Metoprolol?
Metoprolol is a beta blocker medication sold under brand names like Lopressor, Toprol XL, and others. Like other beta blockers, as well as angiotensin-converting-enzyme inhibitors (ACE inhibitors) and calcium channel blockers, Metoprolol can be prescribed to treat high blood pressure and other conditions related to the cardiovascular system: certain types of chest pain (angina), heart failure, an abnormally fast heart rate, or to prevent problems after a heart attack. It can also be prescribed as a treatment for migraines. Rather than a cure for any of these conditions, Metoprolol is a means of managing the problems in order to avoid damaging the circulatory system.
How Does Metoprolol Work?
As a type of beta blocker, Metoprolol works by manipulating the activity of chemicals in the brain and elsewhere in the central nervous system. Many cells in the body have adrenergic receptors on them that are responsive to messages from the nervous system carried by neurotransmitters. These neurotransmitters binding to cells is how the brain can stimulate responses in various parts of the body. In the case of hypertension, adrenaline and noradrenaline being released can exacerbate the problems related to high blood pressure.
By taking a beta blocker like Metoprolol, the receptor sites for adrenaline on the cells of blood vessels and arteries are blocked. This means that adrenaline can’t bind to them and therefore the effect of that neurotransmitter is negated. So instead of adrenaline causing the heart to beat faster and increasing the overall blood pressure in the circulatory system, the medication causes a slowing effect. This then eases pressure throughout the system and prevents the kind of damage that might be caused otherwise.
Side Effects of Metoprolol
Metoprolol has been in use for decades, having been first approved by the Food and Drug Administration (FDA) in 1982. As with other beta blockers, the widespread usage and breadth of experience have made any side effects well documented and understood. In general, the nature of how beta blockers work make them inherently more likely to slow the heart down and cause related symptoms. However, there are also a number of other common side effects:
- blood pressure that is too low (hypotension)
- very slow heart rate (bradycardia)
- feeling lighted or dizzy
- feeling cold in hands or feet
- drowsiness or fatigue
- diarrhea or constipation
- nausea or abdominal pain
- dry mouth
- reduced sex drive
- fluid retention
Whether or not a person has side effects and how intense they are is going to be in part a function of the dosage; the higher the dosage, the more likely the chance of noticeable or disruptive side effects. It is common for people on Metoprolol or other blood pressure medication to, under the direction of a doctor, try different dosages and types of medication until a prescription is found that addresses the condition while causing the fewest number of problems.
Metoprolol and Weight Gain
Weight gain is another potential side effect of taking Metoprolol, though it is unclear whether it can really lead to a substantial increase in body weight. The research done to date has been primarily on beta blockers in general, and it has shown that the magnitude is relatively low; for instance, in one review of numerous studies, the group of subjects on beta blockers had an average weight gain of 2.64 pounds over the duration of the research. In addition to the amount of weight gained being minimal, there is also evidence that the gain is temporary and will stabilize after several weeks.
Any weight gain that is observed is also dependent on the type of beta blocker that is being taken. More specifically, it matters whether the medication is older or newer. Newer beta blockers carvedilol (Coreg) appear to not have any notable effect on body weight. Metoprolol, atenolol (Tenormin), and propranolol are examples of second and first-generation beta blockers that have been associated with weight gain. The difference between the generations of medications is primarily due to the fact that newer types are more selective in the receptors they block.
How Does Metoprolol Lead to Weight Gain?
The reasons why Metoprolol and other beta blockers lead to weight gain are not fully understood, but it’s possible that it could be an indirect effect of some of the other side effects. As noted above, patients sometimes feel fatigue and tiredness when on Metoprolol; when a person feels tired or sluggish, they are less likely to seek physical activity or exercise. As a result, their caloric balance may be off and lead to consuming more calories than are expended. There is also some evidence of beta blocker use and insulin resistance that could affect blood sugar levels and more stored fat.
Research into the effect of Metoprolol on metabolism and blood glucose is still ongoing, so it’s too early to definitely point to that as a reason. The fact that weight levels stabilize for many patients after several weeks of taking the medication may suggest another possible cause, however. When someone is prescribed a beta blocker, they are usually required to cease taking diuretics, which are medications that remove fluid from the body. When they stop taking them, the change can lead to fluid retention along with bloating and swelling; this could also cause a temporary increase in body weight.
What to do if You’ve Gained Weight on Metoprolol
Anyone on Metoprolol who has experienced weight changes should talk to their health care provider; besides being an unwelcome side effect, it may also be an indicator of a deeper problem. There are now numerous options for treating high blood pressure or any of the other conditions that Metoprolol is prescribed for. Depending on the cause of the weight gain, it may be an issue that resolves itself over time as the body adjusts to the medication. There are also minor adjustments to diet and physical activity levels that can bump the caloric balance back into line.
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