Clonidine is an imidazoline derivative and is a Alpha 2 adrenergic agonist, particularly alpha 2a. The hemodynamic effects are due to activation of Alpha 2 (especially alpha 2a) receptors located postjunctionally in the vasomotor centre. This causes decreased central sympathetic outflow which results in bradycardia and fall in BP (also due to increased vagal tone). The plasma NA level decreases. Clonidine is a moderately effective antihypertensive.
It was used as an antihypertensive in the 60’s and 70’s. But due to frequent side effects, it is now rarely used. The other indications include opoid withdrawal, analgesia etc.