What is a shared side effect of both beta blockers and calcium channel blockers?

Dizziness is a shared side effect of both beta blockers and calcium channel blockers, making it the correct answer.

Beta blockers, which primarily work by blocking the effects of adrenaline on beta-adrenergic receptors, can lower heart rate and reduce blood pressure, potentially leading to feelings of lightheadedness or dizziness, particularly when standing up too quickly. Similarly, calcium channel blockers, which inhibit calcium influx into smooth muscle cells, can also cause vasodilation, leading to decreased systemic vascular resistance and a subsequent drop in blood pressure. This, too, can result in dizziness, especially during dosage adjustments or with postural changes.

The other options are not typically associated with these classes of medication. Addiction is not a side effect linked to beta blockers or calcium channel blockers, as they do not have addictive properties. Increased libido is not a common side effect; in fact, some of these medications may have the opposite effect on sexual function. Lastly, hypertension is contrary to the intended effects of both beta blockers and calcium channel blockers, which are used to manage and treat high blood pressure, not cause it.