Overview- Your user-friendly guide for treating low testosterone–from an expert at Harvard Medical School Low testosterone can cause a wide range of symptoms including reduced sex drive, erectile dysfunction, depression, fatigue, muscle loss, impaired cognition, and osteoporosis. This comprehensive and accessible guide from a leading researcher in testosterone therapy covers the most up-to-date information and treatments available. You will learn if hormone replacement therapy is right for you, along with other smart, safe suggestions for leading a healthier, more fulfilling life.