What affects adherence?
The degree of adherence depends on several factors (7). A good relationship between the patient and the clinician is essential. Good, comprehensible information regarding the indications for treatment, its expected effect, possible adverse effects, how the medication should be taken and the duration of treatment are important (6). Patients often obtain information about the prescribed medication from multiple sources. In a study of 328 patients, it was found that more than 80 % had received contradictory information from different sources, including doctors, pharmacists and various mass media sources. Such contradictory information is unfortunate and can lead to reduced adherence (14).
A good relationship between the patient and the clinician is essential
The amount of time spent with the patient is crucial. Brief, hasty consultations have been shown to have a negative effect on adherence (4). Good continuity in the follow-up is also of great importance (2). Adherence tends to be best immediately prior to and after a consultation (6), and close follow-up will therefore often improve adherence.
Stress, forgetfulness, uncertainty regarding the diagnosis, concerns about possible adverse effects, low expectations for the therapeutic effect, fear of addiction and poor understanding of the health risks associated with non-adherence all have a negative effect. Low socioeconomic status, poverty, unemployment, lack of social network, cultural aspects and a number of other factors may also affect adherence negatively (4, 15).
Some patient groups are more susceptible to poor adherence than others. The proportion of the population over 60 years of age is increasing, leading to a greater number of patients with multimorbidity and often complex treatment regimens. Such patients consume approximately 50 % of all prescriptions issued and three times more prescriptions than the general population. This in itself increases the risk of poor adherence, and combined with declining levels of both physical and cognitive functioning, the risk of poor adherence increases even further (4).
Patients with psychiatric disorders have a generally lower level of adherence than those with somatic diseases. Patients who suffer from depression also have a lower rate of adherence to medications that are prescribed for somatic disorders (3, 16). Even sub-clinical depression is a risk factor for poor adherence (2). Some people occasionally forget to take their medication. The effect of this can be reduced if it is possible to prescribe drugs with a long half-life in relation to the dose interval, thus ensuring that the effect persists even when a dose has been forgotten or delayed (6, 17).
Patients with psychiatric disorders have a generally lower level of adherence than those with somatic diseases
Poor adherence is more common in conditions that are asymptomatic and where medication is used prophylactically. An example is the use of statins. Close to one in every six patients who are prescribed a statin never starts the treatment, and after two years, fewer than 60 per cent remain on the treatment. Adherence is poorer for primary prophylaxis than for secondary prophylaxis (17) and declines over time. After six months of treatment, there is often a clear reduction in adherence (6).
It has been shown that adherence increases with decreasing frequency of tablet administration per day. In a meta-analysis of 76 studies, it was found that adherence to medications taken once daily was 79 %, compared to 65 % for medications taken three times daily (18).
Interestingly, placebo-controlled trials have shown that patients who adhere well fare better, irrespective of whether they receive placebo or the study medicine. The fact that patients who adhere to their medication regimen also tend to follow other advice on health and disease ('the healthy adherer effect') shows that good adherence alone is a factor that has a bearing on morbidity and mortality (3, 13).