Objectives:Angiotensin converting enzyme inhibitors (ACEIs) are known to possess different chemical structures, and change in structure of a drug can bring about change in its adverse drug reaction (ADR) profile. The study aims to observe the incidence and severity of ADRs between the di-carboxyl group containing ACEIs (d-ACEIs) versus phosphonate group containing ACEIs (p-ACEIs), in patients suffering from essential hypertension.Materials and Methods:One hundred and twenty patients with essential hypertension were randomized into four groups receiving enalapril, lisinopril, ramipril, and fosinopril. They were followed up for four months, to observe the clinical efficacy along with the associated ADRs.Results:Mild, dry brassy cough (% incidence; 95% CI) was observed with d-ACEIs (6.6%; 0 to 15.6) versus p-ACEI (20%; 5.7 to 34.3), in which the cough observed was moderate-to-severe in intensity and two patients required treatment discontinuation (P < 0.05). No cases of hypotension were observed with the use of d-ACEIs, whereas, two patients on p-ACEI (6.6%; 0 to15.6) had hypotension (P < 0.05). Three patients (10%; 0 to 20.7) on d-ACEIs had nausea, which was not observed with p-ACEI treatment (0%) (P < 0.05).Conclusions:The phosphonate group in p-ACEIs may have a probable relationship with increase in the incidence and severity of ADRs such as dry brassy cough and hypotension. The di-carboxyl group in d-ACEIs may have a probable relationship with increase in the incidence of ADRs like nausea.