**Core Concept**
Alpha 2 agonists are a class of medications that activate alpha 2 adrenergic receptors, leading to various physiological effects. These receptors are G protein-coupled receptors that inhibit the release of neurotransmitters such as norepinephrine and dopamine.

**Why the Correct Answer is Right**
Alpha 2 agonists, such as clonidine and dexmedetomidine, cause sedation, decreased sympathetic tone, and anxiolysis through the activation of alpha 2 adrenergic receptors. This activation leads to a decrease in the release of norepinephrine, resulting in decreased sympathetic activity. Additionally, alpha 2 agonists can cause bradycardia, hypotension, and decreased respiratory rate.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because alpha 2 agonists do not typically cause tachycardia, as they often lead to bradycardia due to decreased sympathetic tone.
**Option B:** This option is incorrect because alpha 2 agonists do not typically cause hypertension, as they often lead to hypotension due to decreased sympathetic tone.
**Option C:** This option is incorrect because alpha 2 agonists do not typically cause increased respiratory rate, as they often lead to decreased respiratory rate due to sedation and decreased sympathetic tone.

**Clinical Pearl / High-Yield Fact**
Alpha 2 agonists, such as clonidine, can be used to manage hypertension, anxiety, and insomnia, making them a useful class of medications in various clinical settings.

**Correct Answer: D.**