The time it takes to experience the desired changes after starting TRT depends on your low T symptoms. For example, men with low libido often have a renewed sex drive about 3 weeks after starting TRT, with sexual performance improving gradually after that for several months. A noticeable increase in lean muscle mass takes about 3 months, with improved bone density occurring after about 12 months and continuing for years. You can read more about how TRT helps you build muscle in a previous blog post.