Dogs raise our serotonin levels, apparently. But a cat would be nice too, if you can't have a dog. I got my dog 12 years ago when I was struggling with depression. She's been a godsend to me and my family. She sleeps on my bed at night. She is always there, always loving, always loyal, always protective, always in need of love and petting. She is a nice presence in our home and life. What a gift she is. I love her to pieces.