Getting the weight down will probably help decrease the pain due to less weight to support. In general for dogs the fastest way to get weight loss is to feed less. If fed the same consistent diet dogs tend to become finely tuned to the amount they eat: Give less, they lose weight. Give more they gain weight. Start by reducing the amount of food by 25%.

Unclear why garlic tablets are being given. There is some evidence in the scientific literature that garlic can lower hypertension through its diuretic effect. Most of the experiments carried out in dogs were in the early 1990s. As with all such experiments involving plant material, what they used is probably not what you can buy at a store. There are also reports that garlic can induce hemolytic anemia in dogs over time.