Phentermine 37.5 mg is a strong drug that starts showing its effect after consumption. Within 2-4 days, you will have a drastic change in your appetite, and it does take around 7-10 days to see its effect fully. The effects include suppression of appetite as well as weight loss. The pill helps uplift your weight loss journey by increasing your metabolism and enabling your cells to burn more calories. The primary effects start after an average of 4 hours of pill consumption. To have the maximum impact, it is recommended that you drink lots of water, stay pretty active throughout, and cut down on carbs.