A medical source statement is an opinion from a Social Security Disability claimant's treating physician concerning the limitations and the severity of the claimant's mental or physical health conditions. In most cases, the medical source statement is simply a form which is signed and filled out by the treating physician or a Consultative Examiner. Under Social Security regulations, the Social Security Administration is supposed to give "controlling" weight to a claimant's own treating doctor and the evidence contained in the Social Security Disability claimant's case rather than information provided from a Consultative Examiner who does not have an ongoing doctor/patient relationship with the claimant. A medical source statement can be one of the best arguments a claimant has to prove they are disabled and unable to work. Although the best type of medical source statements are RFC or residual functional capacity forms which clearly outline, not only the claimant's mental or physical health conditions, but also the types of limitations posed by the conditions and how the claimant's health conditions and symptoms affect the claimant's ability to work (i.e. claimant is unable to sit for more than 2 hours vs. claimant has pain in the lower back).