The objective of this study is to investigate if functional magnetic response imaging (fMRI) can detect the effects of a known pain medicine at over-the-counter doses in people with osteoarthritis (OA) of the knee. The fMRI is a harmless and painless technique that is used in the current study to collect images of brain activity to see if is changed when feeling pain. In this study, BOLD response to mechanical stimulation via pressure stimuli applied to the tibio-femoral joint and patello-femoral in participants with knee OA following four treatment doses of any of three treatment will be compared.