The words adherence and compliance both refer to how well a patient follows the doctor's prescriptions and recommendations, although there are nuances to follow.

The word compliance means simply following the instructions (the patient takes the correct number of doses at the right time for the specified period of time). The word adherence is used when more effort is required from the patient, for example, changing their lifestyle. Adherence is a conscious choice of the patient, taking responsibility for their health.

So, when a patient accidentally misses one or two doses, it is non-compliance. When a patient refuses to take the prescribed drug for some reason, it is non-adherence. When a patient comes to the doctor for a regular check-up, finds out that missing one or two doses from time to time affects the treatment outcomes, and modifies their schedule to avoid missing more doses, they improve adherence, not compliance.

Let's look at three examples.

✒️  Low patient compliance with the allocated treatments can seriously distort the generalizability and validity of controlled clinical trials.

✒️  The study aimed to assess agreement between self-reported and refill compliance to drug treatment among patients with hypertension.

✒️  Treatment adherence includes starting HIV treatment, keeping all medical appointments, and taking HIV medicines exactly as prescribed. For people with HIV, treatment adherence is key to staying healthy. (source)

As you can see, the term adherence is more suitable for real clinical practice, not clinical trials.

The word cooperation is also used as a synonym for adherence in English. Some authors go further and suggest replacing adherence and cooperation with concordance because it more clearly implies informing the patients, agreeing on therapy together, and involving the patient in the decision-making process to improve compliance. Have you encountered this approach in real-life documents?

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