1) Drug: Clonidine

Use:
Hypertension, especially with renal disease

Mechanism:
Clonidine is a centrally-acting α-adrenergic receptor agonist with more affinity for α2 than α1. Stimulates α2 receptors in the brain, which decreases cardiac output and peripheral vascular resistance, lowering blood pressure. It has specificity towards the presynaptic α2 receptors in the vasomotor center in the brainstem. This binding decreases presynaptic calcium levels, and inhibits the release of norepinephrine (NE). The net effect is a decrease in sympathetic tone.

Side Effects:
Short half-life. Sudden discontinuation can cause rebound hypertension. Sedation. Dizziness. Dry-mouth. As mentioned before, Clonidine is a centrally-acting α-adrenergic receptor agonist with more affinity for α2 than α1. Therefore if overdose, it actually can causes hypertension. These effects are seen during an overdose in children, where after taking clonidine their blood pressure increases. As the clonidine is eliminated by the body the peripheral effects wear off and the central hypotensive effects become visible. Both the hypertensive and hypotensive effects can be harmful.

Mnemonic:
"Cl" looks like α. And there are two "i"s in Clonidine. Clonidine is clonning α2. Therefore, it is α2 agonist.


2) Drug: α-Methyldopa
Almost same as Clonidine.

Use:
Hypertension, especially with renal disease

Mechanism:
Stimulates central pre-synaptic α2-adrenergic receptors, and inhibits the release of norepinephrine. -> Decreased peripheral vascular resistance and reduction in cardiac output.
***α-Methyldopa is considered to be safe to use pregnancy for hypertensive blood pressure medication.

Side Effects:
Hemolytic anemia. Hepatitis. Edema. Sedation. Impotence. Dizziness. Dry-mouth.

Mnemonic:
α-Methyldopa starts with α and ends with a. Therefore two α or α2. As you know epi/norepinephrine are derived from DOPA (Tyrosine -> DOPA -> Dopamine -> Norepinephrine -> Epinephrine). If you compare at the molecular structures of α-Methyldopa and DOPA, methyldopa has an extra methyl (CH3) group added to DOPA at carbon #2. Since α-Methyldopa is so similar to DOPA, it will replace DOPA, which now canNOT be made to further derivates of dopamine, norepi and epi due to the presence of extra methyl group.

So it wants to be agonist but blocking out norepi sympathetic effect.
α-Methyldopa = α2 agonist.