What is a common side effect of beta blockers?

Bradycardia is indeed a well-known side effect of beta blockers. These medications work by blocking the effects of adrenaline on beta-adrenergic receptors, which slows down the heart rate. This mechanism is beneficial for individuals with certain cardiovascular conditions, such as hypertension or arrhythmias, as it helps to reduce the heart's workload. However, in some cases, the slowing of the heart rate can become excessive, leading to bradycardia—characterized by a resting heart rate that is too low, typically defined as fewer than 60 beats per minute.

Other options may have plausible connections to beta blockers but do not represent common side effects. Increased energy is unlikely, as beta blockers generally have a calming effect on the heart and can lead to fatigue rather than increased energy levels. Hyperglycemia is more associated with certain other drug classes rather than beta blockers. While weight gain can be a side effect of some beta blockers, it is not as commonly discussed or reported as bradycardia. Therefore, the most accurate answer regarding the side effects of beta blockers is bradycardia.