Most patients miss occasional doses of antihypertensive treatment. The consequent loss of blood pressure (BP) control, and thus increased cardiovascular risk, may be mitigated by prescribing ‘forgiving’ drugs that have a duration of antihypertensive effect beyond the 24-hour dosing interval. However, the consequences of missed doses for cardiovascular outcomes, and additional impact of duration of drug action, have not been evaluated quantitatively. We developed a method to quantify the chain of factors linking adherence and duration of drug action with outcomes; an important consideration given that adherence and hence BP reduction in real-world clinical practice are typically much lower than in randomised controlled trials. The method involves simulating 256-day dosing histories for 1250 individuals, incorporating realistically distributed gaps in dosing based on a study of electronically monitored dosing records from 4783 hypertensive patients in clinical trials. Percentage adherence is adjusted by altering the proportion of doses missed while preserving a realistic distribution of gap length. Systolic BP (SBP) reduction for each patient is estimated, with rises and falls according to the individual’s dosing behaviour. By averaging SBP reductions over time and individuals, population mean SBP reduction is estimated. Cardiovascular disease (CVD) risk over, for example, 10 years may then be predicted using the Framingham Risk Equation, with baseline characteristics from NHANES 2005–2006 (average data: age 65.2 years; 52.9% women; SBP 155.95 mmHg; total cholesterol 5.41 mmol/L) and baseline absolute 10-year CVD risk of 27.0%. The method allows variable inputs including adherence level (%), rate of loss of antihypertensive effect when treatment is interrupted (mmHg/day), rate of BP reduction when treatment is (re)started (mmHg/day) and SBP-lowering effect of uninterrupted treatment (mmHg). In conclusion, we describe a novel method that allows quantification of the effects of treatment adherence and antihypertensive drug forgiveness on clinical outcomes (i.e. SBP and CVD risk reduction).