**Question:** True statement about clonidine are all except?

A true statement about clonidine can be summarized as a synthetic α2-adrenergic agonist with sedative, anxiolytic, and hypotensive effects. It is used in the treatment of hypertension, neuropathic pain, and as an adjuvant analgesic.

**Core Concept:**
Clonidine is a synthetic α2-adrenergic agonist, which means it stimulates α2-adrenergic receptors, resulting in various pharmacological effects. α2-adrenergic receptors are a subtype of adrenergic receptors, found on both pre- and postsynaptic neurons. They play a role in regulating sympathetic activity and blood pressure.

**Why the Correct Answer is Right:**
The correct answer is "A. It has no effect on the heart rate."

Clonidine lowers blood pressure by reducing sympathetic outflow to the heart and vasculature, leading to decreased heart rate. However, its effect on heart rate is minimal compared to its impact on blood pressure.

**Why Each Wrong Option is Incorrect:**

B. "It is a selective α1-adrenergic antagonist."
Clonidine is a non-selective α2-adrenergic agonist, as it binds to both α1 and α2 adrenergic receptors.

C. "It is a strong inhibitor of the respiratory center."
Clonidine does have some effect on the respiratory center, which is part of the medulla oblongata, but its effect is not as strong as it is on other systems, such as the cardiovascular system.

D. "It has no effect on the cardiovascular system."
As mentioned earlier, clonidine does have an effect on the cardiovascular system, particularly reducing blood pressure and heart rate.

**Clinical Pearl:**
Understanding the pharmacodynamics of clonidine is essential for its appropriate use in clinical practice. Its α2-agonist properties make it an effective agent for treating hypertension and pain, but its use should be monitored closely for potential side effects like bradycardia, hypotension, and sedation.