Unfortunately, once you reach your thirties, it’s common for your testosterone levels to decline. You may experience a decrease in energy, endurance, strength, mental sharpness, and sex drive. One solution is testosterone replacement therapy such as injections or a daily patch. Something else you could try is creatine. A New Jersey study found that following a 10 week resistance training program, participants who took a daily creatine supplement significantly increased their resting testosterone levels. If you’re concerned about your testosterone levels, ask your doctor to set up a blood test.