**Core Concept**
Calcium channel blockers (CCBs) are a class of medications used to treat hypertension, angina, and certain arrhythmias. They work by inhibiting the influx of calcium ions into cardiac and smooth muscle cells, leading to vasodilation and reduced cardiac workload.

**Why the Correct Answer is Right**
The most common side effect of dihydropyridine (DH) CCBs, such as nifedipine, is peripheral edema. This occurs due to the vasodilatory effects of these medications, which lead to increased sodium and water retention in the body. The resulting fluid overload causes swelling in the extremities, particularly in the legs. The mechanism involves the blockade of calcium channels in the smooth muscle cells of blood vessels, leading to vasodilation and increased vascular permeability.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because while dizziness is a potential side effect of CCBs, it is not the most common side effect of DH CCBs.
* **Option B:** This option is incorrect because constipation is a potential side effect of non-dihydropyridine CCBs, such as verapamil, but not the most common side effect of DH CCBs.
* **Option C:** This option is incorrect because headache is a potential side effect of many medications, including CCBs, but it is not the most common side effect of DH CCBs.

**Clinical Pearl / High-Yield Fact**
DH CCBs are more likely to cause peripheral edema due to their potent vasodilatory effects. This is in contrast to non-dihydropyridine CCBs, which are more likely to cause constipation and dizziness.

**Correct Answer:** A. Peripheral edema