Testosterone therapy is given over a course of weeks, months and years. Typically, for a first time prescription, you will be prescribed a 10 week or a 20 week program of testosterone therapy. You should start feeling a difference in the first two to four weeks. You will feel the most significant improvements to your energy levels, your strength, moods and sex drive. After the first two to three months of testosterone therapy you should be on the correct dose specifically for you.