Most clinical trials use the Morisky Method as validated measures of medication adherence due to the affordability of administering the scale. Most clinical trials do not have the budget or resources for Directly observed therapy (DOT) to ensure patients take their medication as prescribed and complete their treatment. DOT involves observing drug administration in which a health care professional watches as a person takes each dose of a medication.
The MMAS-8 has undergone numerous levels of validation and has the closest type of validation which mimics the "gold standard", criterion-related validity. The self-reported MMAS-8 agreed with physiological outcome measures such as BP control, HgA1c levels, GFR rates, HDL/LDL ratios, viral load levels, topical skin disorders, etc.
Dr Donald Morisky.