**Core Concept**
The question is testing the interaction of oral contraceptives with other medications that can lead to their failure, causing unintended pregnancy. This involves understanding the pharmacokinetic and pharmacodynamic effects of various substances on the contraceptive efficacy of oral contraceptives.

**Why the Correct Answer is Right**
Oral contraceptives work by inhibiting ovulation, thickening cervical mucus, and altering the endometrium. Certain medications can induce or inhibit the enzymes responsible for metabolizing these hormones, thereby affecting their efficacy. The correct answer is a medication that does not significantly interact with oral contraceptives.

**Why Each Wrong Option is Incorrect**
**Option A:** Griseofulvin is a cytochrome P450 3A4 inducer, which can increase the metabolism of oral contraceptives, leading to their reduced efficacy. Therefore, it is incorrect.

**Option B:** Barbiturates, such as phenobarbital, are also cytochrome P450 3A4 inducers, similar to griseofulvin. They can lead to decreased oral contraceptive levels, making them an incorrect option.

**Option C:** Rifampicin is a potent inducer of cytochrome P450 enzymes, including CYP3A4, which can significantly reduce the levels of oral contraceptives. This makes it an incorrect option.

**Clinical Pearl / High-Yield Fact**
When prescribing oral contraceptives, it is essential to consider potential interactions with other medications that may affect their efficacy. Patients should be advised to use alternative or additional contraceptive methods if they are taking medications that interact with oral contraceptives.

**Correct Answer:** D.