Compliance (medicine)
Compliance (or Adherence) in a medical context refers to a patient both agreeing to and then undergoing some part of their treatment program as advised by their doctor or other healthcare worker. Most commonly it is whether a patient takes their medication (Drug compliance), but may also apply to use of surgical appliances (e.g. compression stockings), chronic wound care, self-directed physiotherapy exercises, or attending for a course of therapy (e.g. counselling).
It has been estimated that in developed countries only 50% of patients who suffer from chronic diseases adhere to treatment recommendations.  Compliance rates during closely monitored research studies are usually far higher than in later real-world situations (e.g. up to 97% compliance in some studies on statins, but only about 50% of patients continue at six months).
One third of patients with hypertension resitant to triple therapy may be noncompliant.
Nonadherence may affect the patient's own immediate health or have implications for the wider society (e.g. failure to prevent complications from chronic diseases, formation of resistant infections or untreated psychiatric illness).

# Terminology
It has been estimated that half of those for whom medicines are prescribed do not take them in the recommended way. Until recently this was termed "non-compliance", which was sometimes regarded as a manifestation of irrational behavior or willful failure to observe instructions, although forgetfulness is probably a more common reason. But today, health care professionals prefer to talk about "adherence" to a regimen rather than "compliance". The word adherence may be preferred by many health care providers, because compliance suggests that the patient is passively following the doctors orders and that the treatment plan is not based on a therapeutic alliance or contract established between the patient and the physician. According to some, both terms are imperfect and uninformative descriptions of medication-taking behavior.

# Causes
Causes for poor compliance include:
- Forgetfulness
- Prescription not collected or not dispensed
- Purpose of treatment not clear
- Perceived lack of effect
- Real or perceived side-effects
- Instructions for administering not clear
- Physical difficulty in complying (e.g. with opening medicine containers, handling small tablets or swallowing difficulties, travel to place of treatment)
- Unattractive formulation (e.g. unpleasant taste)
- Complicated regimen
Dose frequency. The following are a set of estimates of proportion of days compliant:
Once daily 84%
Twice daily 75%
Three times daily 59%
- Dose frequency. The following are a set of estimates of proportion of days compliant:
Once daily 84%
Twice daily 75%
Three times daily 59%
- Once daily 84%
- Twice daily 75%
- Three times daily 59%
- Cost of drugs

# Detection
Non-adherence can be detected by validated questionnaires and by assessing refill records.
Medication levels may be needed.
In hypertension, patients with non-compliance may have a higher white coat effect.

## Assessment of refill records
When refill records are accessible, many metrics can be calculated. The two most common are:
- Medication Possession Ratio (MPR): "the sum of the days supply for all fills of a given drug in a time period divided by the number of days in the time period"
- Proportion of Days Covered (PDC) is the same as the MPR but adjusts for days with double coverage of medications due to early refills.
The PDC is recommended by Medicarethe National Quality Forum (NQF)
- The PDC is recommended by Medicarethe National Quality Forum (NQF)
Providing refill information to health care providers can reduce clinical inertia and improve the quality of prescribing.

## Questionnaire
Available surveys include:
- MMAS-4 (4 items). Copyrights have been reported contested for the MMAS-4
- Morisky Medication Adherence Scale, derived from MMAS-4 (8 items)
- Brief Adherence Rating Scale (BRS)
- The Adherence Estimator (3 items) developed by Merck Sensitivity was 88% if medium or high risk scores were combined and interpreted as abnormal.

# Interventions
Interventions to improve adherence have been reviewed.

# Concordance
Concordance is an approach at involving the patient in the treatment process to improve compliance and is a current UK NHS initiative. The patient, being informed about the condition and the various treatment options, is  jointly involved in the decision as to which course of action to take and partially responsible for the monitoring and reporting back to others involved in their care. Compliance with treatment is improved by:
- Only recommending treatments that are effective in circumstances when they are required
- Selecting treatments with lower levels of side effect or concerns for long-term use
- Prescribing the minimum number of different medications, e.g. prescribing for someone with two concurrent infections a single antibiotic that addresses the sensitivities of both likely bacteria, rather than two separate courses of antibiotics. However, this also raises the spectre of developing antibiotic resistant species in the wider scenario.
- Simplifying dosage regimen, whether by selecting a different drug or using a sustained release preparations that need less frequent dosages during the day.
- Explanation of possible side effects and whether important to continue with the course of medication none-the-less.
- Advice on minimising or otherwise coping with side effects, e.g. advice on whether to take a particular drug on an empty stomach or with food.
- Developing trust between the patient and their doctor such that patients do not feel they will be embarrassed or seen as ungrateful if they are unable to take a particular drug, thus allowing a better tolerated alternative preparation to be tried.