DEAR DOCTOR K: I’m a man in my early 50s. Lately, my sex drive isn’t what it used to be. Plus, I’m irritable and depressed. Could I have low testosterone?

DEAR READER: Yes, you could, but that’s not the only possible explanation of your symptoms. There are some rare diseases that can cause very low blood levels of testosterone and a host of symptoms. I won’t be talking about those in this column. Instead, I’m talking about a more common condition.

Testosterone is the major sex hormone in men. As men get older, testosterone production falls. If it falls low enough, it can cause some of the symptoms you described.