**Core Concept**
The question tests the knowledge of antimalarial drugs and their potential side effects, particularly neuropsychiatric adverse reactions. Mefloquine is a medication used to prevent and treat malaria, and it has been associated with various neurological and psychiatric side effects.

**Why the Correct Answer is Right**
Mefloquine's mechanism of action involves interfering with the parasite's ability to metabolize hemoglobin, which ultimately leads to the death of the parasite. However, mefloquine can also affect the human brain, leading to neuropsychiatric side effects such as anxiety, depression, psychosis, and seizures. This is thought to be due to mefloquine's ability to cross the blood-brain barrier and interact with various neurotransmitter systems.

**Why Each Wrong Option is Incorrect**
**Option A:** Artesunate is a fast-acting antimalarial drug that works by destroying the parasite's ability to synthesize heme. It is generally well-tolerated and not associated with significant neuropsychiatric side effects.
**Option B:** Aemisinin is the active ingredient in artemisinin-based combination therapies, which are effective against malaria. It is not typically associated with neuropsychiatric side effects.
**Option C:** Quinine is an older antimalarial drug that has been used for centuries to treat malaria. While it can cause various side effects, including cinchonism and hypoglycemia, it is not typically associated with neuropsychiatric side effects.

**Clinical Pearl / High-Yield Fact**
Mefloquine is contraindicated in patients with a history of seizures, psychiatric disorders, or cardiovascular disease. It is also not recommended for patients taking certain medications that can interact with mefloquine, such as beta-blockers and antidepressants.

**✓ Correct Answer: D. Mefloquine**