Depression has many features which are intensely physical in nature. Many of these symptoms and signs are very similar to symptoms seen in diseases which are known to have an identifiable physical cause. These physical symptoms of depression include aches and pains, weight loss, constipation, tiredness always tired, More about tiredness ), loss of appetite, loss of interest in sex (more) and others. It can therefore be difficult for both patients and doctors to be certain whether a physical symptom is representative of depression, or suggests an entirely different disorder requiring a different treatment.

In addition because it is sometimes considered unacceptable to be psychologically ill, physical symptoms are often used as substitutes for psychological ones, particularly the more minor variations in mood. Many cultures express mood changes in concrete body terms, including descriptions of pains, for example. Many patients feel that doctors are trained to respond to bodily complaints and hence present these unconsciously to their doctors.

It is well known that common physical complaints can have a psychological contribution. Headaches, for instance, can be made worse by the increase in muscular tension of the neck and scalp muscles which are a physical accompaniment of a state of anxiety. In the more severe forms of depression not only are very physical symptoms such as slowness and constipation present, but worries about their physical state can increase in patients until they imagine they are ill when they are not, sometimes to the point of delusion.