Which of the following is a hormone replacement therapy?

Vivelle-Dot is a hormone replacement therapy that is specifically designed to deliver estradiol, a form of estrogen, through the skin. This is especially beneficial for individuals experiencing menopause or other conditions that necessitate estrogen supplementation. Hormone replacement therapy is commonly used to alleviate symptoms associated with decreased hormone levels, such as hot flashes, night sweats, and vaginal dryness.

The reason why this answer stands out in the context of the other choices is that Calan, Tegretol, and Lunesta serve different purposes. Calan is primarily used as a calcium channel blocker for blood pressure control and heart rhythm issues. Tegretol is an anticonvulsant utilized to manage seizures and certain types of nerve pain. Lunesta is a sedative primarily prescribed for the treatment of insomnia. These medications do not function as hormone replacement therapies and are not designed to replace or supplement hormones in the body. This distinction makes Vivelle-Dot the appropriate answer to the question.