Bethanidine is a post-ganglionic adrenergic neurone-blocking agent which exerts a marked postural hypotensive effect. The precise mechanism whereby bethanidine causes blockade of adrenergic neurones is unknown. An initial sympathomimetic effect has been demonstrated in man and animals, possibly due to release of catecholamines.

Debrisoquin is an antihypertensive drug having guanethidine-like properties, which inhibits monoamine oxidase (MAO) and does not enter the brain. Debrisoquine was used for the treatment of hypertension. Debrisoquine hydroxylation phenotype has been the most used test in humans to evaluate CYP2D6 activity. Two debrisoquine hydroxylation phenotypes have been described: poor and extensive metabolizers. A group with a very low debrisoquine metabolic ratio within the extensive metabolizers, named ultrarapid metabolizers, has also been distinguished. This CYP2D6 variability can be for a large part alternatively determined by genotyping, which appears to be of clinical importance given CYP2D6 involvement in the metabolism of a large number of commonly prescribed drugs.

Guanoxan is 2-guanidinomethylbenzo-1,4-dioxan. It acts as a blocker of alpha-2 adrenoceptors. The clinical use of this drug has been in the treatment of hypertension. Both systolic and diastolic pressures are lowered in the lying and standing positions.

Guanazodine is a new antihypertensive drug. Guanazodine caused a sustained decrease in the systemic blood pressure of spontaneously hypertensive rats, renal hypertensive dogs and normal cats. No tachyphylaxis developed when the drug was administered orally. The heart rate decreased. Guanazodine relaxed the cat nictitating membrane, attenuated the positive chronotropic response to sympathetic nerve stimulation in anesthetized dogs and in isolated rabbit aorta to transmural electrical stimulation. Guanazodine potentiated the pressor response to noradrenaline but attenuated the response to tyramine in anesthetized cats. It may be concluded that the hypotensive effect of guanazodine is related to adrenergic neuron blocking action, the noradrenaline-depleting action in peripheral tissues is similar to the effect of guanethidine and bethanidine. However, this drug is less potent than guanethidine. Toxicity and side effects appear to be less with guanazodine than with guanethidine and bethanidine.

Guanoclor is an anti-hypertensive agent developed by Pfizer Ltd. (U.K.). It seems to be effective in various types of hypertension (unknown aetiology, renal, and malignant). It affects both systolic blood-pressure and diastolic blood-pressure. It is an adrenergic neurone-blocking agent, which also interferes with noradrenaline synthesis by inhibition of the enzyme dopamine beta-hydroxylase. Clinical use of the compound was first reported by Lawrie et al. (1964), who achieved satisfactory blood-pressure control in 60% of their cases with guanoclor alone, and in a further 18% with the addition of a thiazide diuretic. They also noted a significant reduction in urinary noradrenaline levels during guanoclor administration. Guanochlor has an affinity for the Na+/H+ exchanger ranging between 0.5 uM and 6 uM in different systems and is more potent than amiloride in all systems studied. It is suggested that guanochlor recognizes a binding site on the Na+/H+ exchanger that is distinct from the amiloride binding site.

Guanoxabenz is an antihypertensive drug that was in clinical use in the 1980s. It acts as a selective agonist of alpha2A1 and alpha2B1 adrenergic receptors. Guanoxabenz is the main metabolite of the FDA-approved drug guanabenz.

Guanethidine belongs to the general class of medicines called antihypertensives. It was used to treat high blood pressure (hypertension). It is believed to act mainly by preventing the release of norepinephrine at nerve endings and causes depletion of norepinephrine in peripheral sympathetic nerve terminals as well as in tissues. It is taken up by norepinephrine transporters. It becomes concentrated in NE transmitter vesicles, replacing NE in these vesicles.