Every person responds differently to antidepressant medicine. It’s impossible to know which is the right one to take before you try it.

But if all antidepressants are considered roughly equal in their effect, how can this be? Here’s the answer: Drug A may help 65 out of 100 people who are depressed. Drug B may also help 65. But not the same 65.

In other words, some people are helped by both drugs. Some are helped by only A or B. And some get no relief at all.

It gets even more complicated when you consider that there are dozens of drugs available for treating depression — not just two.

I’ll give you another issue to consider. A common reason people don’t get better with treatment is that they stop taking the drug because of side effects.

Side effects are often mild, but they vary from drug to drug. Common ones are nausea, diarrhea, weight gain and sexual side effects. But many people stop taking their medicine even when the side effects are mild. They get discouraged and don’t try a different drug.

Choosing an antidepressant is a trial-and-error process. This means your first drug prescribed may or may not effectively treat depression. Or it may cause mild side effects. Therefore, I suggest picking a drug based on which side effects you most want to avoid.

If you start a drug and feel uncomfortable, tell your doctor. You can try a different medicine. The real challenge, of course, is that depression has so many causes. We cannot predict who will respond to a particular drug. We don’t know in advance what unwanted effects will happen.

If you and your doctor work together patiently, there is a good chance that one of the many drug options will be the right one for you.

And don’t forget about psychotherapy. In many instances, it is as effective as medicine. And the combination of medicine and psychotherapy has proven to be the most effective strategy of all.