Why people miss doses: what the research says

A common problem, not a personal failing

Missing doses of a long-term medicine is very common. In developed countries, adherence to long-term therapy for chronic illness averages around 50% (WHO, 2003). The World Health Organization report found that rates in developing countries are even lower¹.

Missed doses carry real costs. Non-adherence is associated with up to 10% of US hospital admissions, and accounts for 33 to 69% of medication-related hospitalisations. Both figures are US estimates^{1, 2}.

It is tempting to see this as a question of willpower. The research does not support that view. The WHO report puts it plainly: patients "need to be supported, not blamed"¹.

Five kinds of reasons

The WHO groups the reasons people miss doses into five dimensions¹:

• Social and economic factors, such as the cost of medicines, poverty and a lack of social support.
• Healthcare team and system factors, such as short consultations and limited follow-up.
• Condition-related factors, such as how severe the symptoms are.
• Therapy-related factors, such as a complex regimen, frequent changes in treatment and side effects.
• Patient-related factors, such as forgetfulness, worries about side effects and doubts about whether a treatment works.

A later study brought together 51 systematic reviews on the same question. It identified 771 individual factors linked to adherence, and none of them predicted adherence on its own³. The authors also stressed that non-adherence should not be seen as the patient's fault alone³.

Forgetting, side effects and cost

When people are asked directly, forgetting comes up most often. In one survey of 10,000 patients, 24% gave forgetfulness as a reason for missing medicines⁴. Another 20% cited perceived side effects, 17% high drug costs, and 14% a sense that the medicine would make little difference⁴.

Researchers often divide missed doses into two kinds. Unintentional ones include forgetting a dose, forgetting a refill or misunderstanding the schedule. They tend to become more common as regimens become more complex⁵. Intentional ones involve a decision to stop or change a medicine. That decision may be shaped by cost, side effects, beliefs about the illness or expectations of improvement⁵.

The line between the two is not always clear. The WHO notes that what looks like forgetting can sometimes reflect deeper beliefs and priorities about medicines¹.

Cost deserves its own mention. The WHO lists the high cost of medication among the social and economic factors, alongside the cost of transport to a treatment centre¹.

Beliefs, complexity and feeling well

Beliefs about medicines play a large part. A meta-analysis of 94 studies, covering 25,072 people with long-term conditions, looked at two kinds of belief⁶. People who felt a stronger personal need for their treatment tended to have higher adherence. People with more concerns about it tended to have lower adherence⁶.

The WHO describes what those concerns often are. They include worries about side effects, disruption to daily life, long-term effects and becoming dependent on a medicine¹.

Complexity matters too. The WHO names the complexity of the regimen, the length of treatment and frequent changes among therapy-related factors¹. The review of reviews repeatedly found complex or frequent dosing schedules, and the number of tablets, linked to lower adherence³.

Finally, some conditions do not feel like illnesses. Most people with high blood pressure do not feel any symptoms⁷. In that situation, side effects can seem worse than the condition itself. The WHO calls the treatment of high blood pressure "a classic example" of this¹. People who start to feel better may also decide that they no longer need their medicine¹.

Why the reason matters

Because the reasons differ, no single fix suits everyone. The WHO recommends looking at all five dimensions, rather than focusing on the patient alone¹.

It can help to notice which reason applies to you. Is it forgetting, a side effect, the cost or a doubt about the medicine? Each one is worth raising with your care team. The WHO notes that a patient often has good reasons for not following a plan. A doctor can then adjust the plan after a frank discussion¹.

If something is getting in the way, talk to your doctor or pharmacist before changing how you take a medicine.

This article is general information, not medical advice. Talk to your doctor or pharmacist about your own medicines.