**Core Concept**
Ketamine is a medication primarily used for starting and maintaining anesthesia. It induces a trance-like state while providing pain relief, sedation, and memory loss. The disadvantage of ketamine is related to its effects on the central nervous system and potential for side effects.

**Why the Correct Answer is Right**
Ketamine can cause hallucinations, delirium, and dissociation from reality, which are particularly concerning in patients with a history of psychiatric disorders or those who are prone to psychosis. This is due to its action on the N-methyl-D-aspartate (NMDA) receptors in the brain, which can lead to an imbalance in neurotransmitter activity. Additionally, ketamine can cause increased heart rate, blood pressure, and respiratory rate, making it less ideal for patients with cardiovascular or respiratory issues.

**Why Each Wrong Option is Incorrect**
**Option A:**
This option is incorrect because ketamine does not typically cause hypotension (low blood pressure) as a primary disadvantage. While it can cause vasoconstriction, its primary concern is related to central nervous system effects.

**Option B:**
This option is incorrect because ketamine is actually used for its analgesic properties, particularly in the management of acute pain. Its analgesic effects are mediated through NMDA receptor antagonism.

**Option C:**
This option is incorrect because ketamine does not typically cause significant respiratory depression as a disadvantage. While it can cause respiratory rate increase, its primary concern is related to central nervous system effects.

**Clinical Pearl / High-Yield Fact**
Ketamine should be used with caution in patients with a history of psychiatric disorders, such as schizophrenia or bipolar disorder, as it can exacerbate psychotic symptoms.

**Correct Answer:** D.