**Core Concept**
Opioids and monoamine oxidase inhibitors (MAOIs) interact through complex mechanisms, primarily involving the inhibition of monoamine oxidase enzymes. MAOIs block the breakdown of monoamines like serotonin, norepinephrine, and dopamine, leading to increased levels. Opioids can also affect these neurotransmitters, potentially exacerbating the effects of MAOIs.

**Why the Correct Answer is Right**
The correct answer is **C. Tramadol**. Tramadol is a unique opioid that inhibits the reuptake of norepinephrine and serotonin, in addition to its agonist effects on mu-opioid receptors. When combined with MAOIs, tramadol can lead to a dangerous increase in the levels of these neurotransmitters, resulting in serotonin syndrome or a hypertensive crisis. This is because MAOIs block the breakdown of these neurotransmitters, while tramadol increases their release.

**Why Each Wrong Option is Incorrect**
**Option A:** **Fentanyl** is not typically contraindicated with MAOIs. Fentanyl is a potent opioid agonist that primarily acts through mu-opioid receptors, without significant effects on monoamine reuptake or breakdown.

**Option B:** **Morphine** is not typically contraindicated with MAOIs. Morphine is a mu-opioid agonist that does not significantly affect the levels of monoamines like serotonin or norepinephrine.

**Option D:** **Meperidine** is contraindicated with MAOIs, but for a different reason. Meperidine is metabolized to normeperidine, which can accumulate in patients with renal impairment and interact with MAOIs. However, this is not the same concern as with tramadol.

**Clinical Pearl / High-Yield Fact**
When combining opioids with MAOIs, it's essential to consider the specific pharmacological profile of each opioid. Tramadol's unique mechanism of action makes it a high-risk combination, while other opioids like fentanyl and morphine are generally safer.

**Correct Answer: C. Tramadol**