Again, this should not be applied too soon after the injury but light rubbing seems to initiate pain relief by the gate theory mechanism. Product selection Drug therapy for sprains and strains can be systemic or topical. Neither require comment in this section as they are well documented elsewhere. Their mode of action is not clearly established, but one theory has already been discussed. P from the sensory nerve endings.
Some counterirritants also have a rubefacient effect, that is they produce local vasodilation.
The increased blood flow may produce local temperature elevation which is also counterirritant. Caution must be exercised in interpreting the physiological effect of these drugs since there is a strong psychological component in pain relief. It could well be that the warming effects and the odour associated with many of the preparations used in this manner have an important placebo activity. They are believed to exert their action by the same mechanism proposed for their systemic administration. As they are absorbed, the same cautions apply for asthmatics and stomach damage.