Medically unexplained physical symptoms (MUPS or MUS) are symptoms for which a treating physician or other healthcare providers have found no medical cause, or whose cause remains contested. In its strictest sense, the term simply means that the cause for the symptoms is unknown or disputed—there is no scientific consensus. Typically, the possibility that MUPS are caused by prescription drugs or other drugs is ignored. However, in practice, most physicians and authors who use the term consider that the symptoms most likely arise from psychological causes. It is estimated that between 15% and 30% of all primary care consultations are for medically unexplained symptoms. A large Canadian community survey revealed that the most common medically unexplained symptoms are musculoskeletal pain, ear, nose, and throat symptoms, abdominal pain and gastrointestinal symptoms, fatigue, and dizziness. The term MUPS can also be used to refer to syndromes whose etiology remains contested, including chronic fatigue syndrome, fibromyalgia, multiple chemical sensitivity and Gulf War illness.
Many patients presenting with medically unexplained symptoms also meet the diagnostic criteria for anxiety and/or depression. The likelihood of meeting such criteria increases with the number of unexplained symptoms reported. However, anxiety and depression are also very common in individuals with medically explained illnesses, and again, the likelihood of a person receiving one of these diagnoses increases with the number of symptoms reported. Consequently, on the current evidence, we cannot infer that anxiety or depression are causes of medically unexplained physical symptoms.
Physical symptoms have been associated with adverse psychosocial and functional outcome across different cultures, irrespective of etiology (either explained or unexplained).
The lack of known etiology in MUPS cases can lead to conflict between patient and health-care provider over the diagnosis and treatment of MUPS. Most physicians will consider that MUPS most probably have a psychological cause (even if the patient displays no evidence of psychological problems). Many patients, on the other hand, reject the implication that their problems are "all in their head", and feel their symptoms have a physical cause. Diagnosis of MUPS is seldom a satisfactory situation for the patient, and can lead to an adversarial doctor-patient relationship. The situation may lead a patient to question the doctor's competence.