Over the past 25 years, for people without a fixed abode, shocking mortality outcomes have persisted: in 1992, one study showed mortality was 3 times higher with an average age of death at 47 years; and in 2009, the all cause mortality hazard ratio was 4.4. In 2011, the average age of death had decreased to 40.5 years. Homelessness confers an increased risk of dying from drug misuse, circulatory and respiratory disorders, infections and external factors. Part of the excess mortality may be explained by exposure to co-existing risk factors e.g. alcohol and co-morbid Long Term Conditions (LTCs) including mental illness. Multimorbidity develops earlier. Levels of multimorbidity are higher, and the impact is more severe with a negative impact on functional status, increased and poorly co-ordinated use of health services, and increased healthcare costs. Recent work in Glasgow suggested levels of multimorbidity in a homeless population registered with a general practice, comparable to patients aged 84 years in mainstream practices, despite an average age of 43 years. Emergency department attendances are five times greater, with admissions and duration of hospitalisation three times greater. Low prescribing and use of medicines for prevention of health crises may contribute to high emergency service usage for LTCs instead of primary care services. Maximising opportunities for engagement in health care and optimal prescribing and use of medicines for LTCs is therefore important. For multiple reasons, still poorly understood but likely to be related to complex medical, psychological and social factors, patients present less to their GP for accrual of formal diagnoses of LTCs.

In addition, people who are homeless are 40 times more likely than a housed person, not to be registered with a GP. There are significant unmet health needs and high rates of missed scheduled appointments which are likely to worsen health and further increase costs. Possible reasons for this include barriers to accessing healthcare services, caused by patient level (emotional e.g. priority setting in the context of a chaotic lifestyle), system level (e.g. health service organisation) and provider level (e.g. environmental barriers). People who are homeless tend not to obtain preventative care, appearing when sick or injured, or when in need of medicines for pain or mental distress.Initiation, dose up-titration, storage and adherence with medicines are more challenging for people who are homeless.

In addition to the excess burden of complex multimorbidity that homeless people experience, intersections with addictions and criminal justice have recently been explored. ‘Severe and Multiple Disadvantage’ (SMD) has emerged as a descriptor of the problems faced by individuals in contact with housing, addiction services, and the criminal justice system with underlying poverty being pervasive and mental illness often contributory. Adverse childhood experiences are considered often at the root of SMD.