Angiotensin receptor blockers (ARBs) and angiotensin-converting enzyme (ACE) inhibitors are two types of drugs routinely used to treat hypertension, but they function in distinct ways.

Mechanism of action:

ACE Inhibitors function by inhibiting the action of angiotensin-converting enzyme (ACE), which converts angiotensin I to angiotensin II. Angiotensin II is a powerful vasoconstrictor that also increases the release of aldosterone, causing salt and water retention and contributing to high blood pressure. ACE inhibitors suppress the synthesis of angiotensin II, resulting in vasodilation and decreased aldosterone secretion.
ARBs: Angiotensin receptor blockers (ARBs) inhibit the function of angiotensin II at its receptors, specifically the angiotensin II type 1 (AT1) receptors.

Effect on Kinins:

ACE inhibitors prevent not only the conversion of angiotensin I to angiotensin II, but also the breakdown of bradykinin, a vasodilator peptide. The dual action of ACE inhibitors causes elevated levels of bradykinin, which contributes to their vasodilatory effects but can also produce adverse effects such as cough and angioedema.
ARBs do not influence bradykinin levels because they inhibit angiotensin II receptors without decreasing ACE function. As a result, ARBs do not have the same side effects associated with bradykinin buildup as ACE inhibitors.

Efficacy and tolerability

Both ACE inhibitors and ARBs are effective at lowering blood pressure and decreasing the risk of cardiovascular events in hypertensive patients. Individual responses to various drugs may vary, and some individuals may benefit more from one class than the other.
Tolerability, the presence of certain comorbidities (e.g., heart failure, kidney disease), and potential drug interactions are all important considerations when choosing between ACE inhibitors and ARBs.
ACE inhibitors may be associated with a higher prevalence of adverse effects such as cough and angioedema than ARBs, especially in patients of specific ethnicities (e.g., African heritage).
In summary, both ACE inhibitors and ARBs efficiently lower blood pressure by targeting the renin-angiotensin-aldosterone pathway, although they differ in their methods of action.