Because most of the care needed for chronic conditions is based on patient self-management (usually requiring complex multi-therapies (54), the use of medical technology for monitoring and changes in the patient's lifestyle (55), patients face several potentially life-threatening risks if health recommendations are not followed as they were prescribed. Some of the risks faced by patients who adhere poorly to their therapies are listed below.
More intense relapses. Relapses related to poor adherence to prescribed medication can be more severe than relapses that occur while the patient is taking the medication as recommended, so persistent poor adherence can worsen the overall course of the illness and may eventually make the patients less likely to respond to treatment (56).
Increased risk of dependence. Many medications can produce severe dependence if taken inappropriately by patients. Good examples are diazepam (57) and opioid-related medications.
Increased risk of abstinence and rebound effect. Adverse effects and potential harm may occur when a medication is abruptly discontinued or interrupted. Good adherence plays an important role in avoiding problems of withdrawal (e.g. as seen in thyroid hormone replacement therapy) and rebound effect (e.g. in patients being treated for hypertension and depression), and consequently decreases the likelihood that a patient will experience adverse effects of discontinuation (58, 59).
Increased risk of developing resistance to therapies. In patients with HIV/AIDS, the resistance to antiretroviral agents has been linked to lower levels of adherence (48,60). Partial or poor adherence at levels less than 95% can lead to the resumption of rapid viral replication, reduced survival rates, and the mutation to treatment-resistant strains of HIV (61). The same happens in the treatment of tuberculosis where poor adherence is recognized as a major cause of treatment failure, relapse and drug resistance (62,63).
Increased risk of toxicity. In the case of over-use of medicines (a type of nonadherence), patients are at an increased risk of toxicity, especially from drugs with accumulative pharmacodynamics and/or a low toxicity threshold (e.g. lithium). This is particularly true for elderly patients (altered pharmacodynamics) and patients with mental disorders (e.g. schizophrenia).
Increased likelihood of accidents. Many medications need to be taken in conjunction with lifestyle changes that are a precautionary measure against the increased risk of accidents known to be a side-effect of certain medications. Good examples are medications requiring abstinence from alcohol (metronidazole) or special precautions while driving (sedatives and hypnotics).