**Core Concept**
Rifampicin is a potent inducer of the cytochrome P450 enzyme system, particularly CYP3A4. This enzyme induction leads to an increase in the metabolism of various drugs, including oral contraceptive pills (OCPs), thereby reducing their efficacy.

**Why the Correct Answer is Right**
The increased metabolism of OCPs by rifampicin is a result of its ability to induce the expression of CYP3A4 enzymes. This induction enhances the breakdown of the hormones estrogen and progesterone, which are essential components of OCPs. As a consequence, the plasma concentrations of these hormones decrease, making the OCPs less effective in preventing ovulation. The enhanced metabolism of OCPs by rifampicin can lead to contraceptive failure, resulting in an increased risk of unintended pregnancy.

**Why Each Wrong Option is Incorrect**
**Option A:** Decreased absorption of OCPs is not a known mechanism of rifampicin-induced OCP failure. Rifampicin's effect on OCP metabolism is primarily due to enzyme induction, not altered absorption.

**Option B:** Rifampicin does not increase the binding of OCPs; rather, it enhances their metabolism. The reduced free drug concentration is a consequence of increased metabolism, not increased binding.

**Option D:** Rifampicin does not directly increase the chances of ovulation. Its effect on OCPs is primarily through enhanced metabolism, leading to reduced hormone levels and decreased contraceptive efficacy.

**Clinical Pearl / High-Yield Fact**
When prescribing OCPs to patients taking rifampicin or other CYP3A4-inducing medications, consider using alternative contraceptive methods or adjusting the OCP dose to maintain efficacy.