Having a daily timetable for taking medication and taking all doses exactly as prescribed is the traditional definition of adherence, also known as compliance. This may sound simple, but in the case of Highly Active Antiretroviral Treatment (HAART), it is not.

For those who want an effective response to HAART, daily, near-perfect adherence (>95%) to a dosing schedule is required. This includes adhering to instructions as to whether a drug is taken on an empty stomach or with food; taking all drugs as prescribed, including the ones that may cause uncomfortable side-effects; and taking each drug at the correct dosing time, so that there is a specified interval between each dose when necessary. This calls for a high level of precision, consistency, and commitment on the part of the patient over time.

These efforts are necessary because viral replication cannot be not be suppressed if drug levels in the bloodstream are too low. With incomplete viral suppression, HIV can continue damaging the immune system and drug resistance to a medication or even a whole class of medication can develop. Additionally, suboptimal adherence increases both the risk of transmission and the risk of transmitting drug-resistant virus to others. If drug levels are too high (doses taken too closely together) toxicities and unnecessary side-effects may occur.

The idea of ‘readiness’ for therapy is a major consideration before starting any treatment because of the high risk of developing drug resistance with incomplete adherence. The healthcare provider or team and the patient need to discuss the goals and demands of treatment and the potential side-effects that may occur. If treatment is still desired, then the optimal regimen for that patient needs to be chosen. This will depend on drug availability; the results of viral genotyping, if available; and the patient’s assessment of what regimen will be best for them (most effective? fewest pills? least number of side-effects?). Practical discussions on how to incorporate pill-taking into the patient’s normal daily schedule should take place before any treatment is started.

Information and preparation may include discussion with doctors, nurses, pharmacists, peer educators, social workers, treatment supporters, community-based workers, members of support groups, and volunteers. Every treatment setting will vary in what it is able to offer to patients in the way of support.

Predictors of successful adherence include a sense of trust between the patient and caregiver and a shared belief in the efficacy of the regimen selected. Clinician qualities found to encourage adherence were skill, knowledge, and experience as well as the willingness and ability to educate and support patients on an on-going basis.

The benefits of correct adherence to therapy include an improved quality of life through reduction in number of illnesses, hospitalisation events, rate of disease progression, and mortality. Because of these factors, adherence has been intensely studied in the past decade. Results of this research have altered, to some degree, how drugs are formulated and the scope of the patient/caregiver relationship. Pharmaceutical companies were urged to develop drugs with simpler dosing schedules (optimally, once-daily dosing with no food restrictions) and a longer half-life (referring to the amount of time the drug is active in the body).

In resource-limited areas, studies have shown that adherence and therapeutic outcomes are similar or superior to results in developed countries if there is consistent, available access to both care and medication. Regardless of the setting, predictors of adherence success include the commitment, motivation, and preparation of the person starting on therapy and/or sustaining a successful regimen combined with ongoing information, simplified dosing schedules, and support.