Great sex -- if it is within a mutually monogamous relationship -- may be one of the ultimate mood boosters.

In fact, semen contains powerful -- and potentially addictive -- mood-altering chemicals, including testosterone, estrogen, prolactin, luteinizing hormone, and prostaglandins. So although sex won't cure depression, it may boost mood if some of these chemicals are absorbed through the walls of the vagina.

Sex is only a mood booster if it's safe, mutually monogamous sex. Although women who do not use condoms during sex are less depressed, according to research, that doesn't mean they should practice unsafe sex. Studies have found no correlation between high-risk sexual behavior and lower rates of depression.

And good sex isn't the only recipe for happy days and contented nights. Feel free to explore other options, like volunteering, exercising regularly, spending time with good friends, laughing with loved ones, writing in a journal, and otherwise engaging in activities that you find fulfilling. Taking good care of your health can also make you happy. After all, nothing can put a smile on your face like a good report from your doctor.

What does the doctor recommend for your lifestyle? Take this disease prevention assessment and find out.