First of all, your doctor's advice sounds reasonable. If treatment for a first episode of depression worked, psychiatrists often recommend continuing that treatment for at least 6 months. Then many people try to taper their medications to see if they can do without them.

But having depression return is quite common. That's because the treatments for depression — medication, psychotherapy or a combination of the two — do not permanently change the underlying biology of mood enough to keep symptoms at bay.

If depression returns, it is not necessarily more dangerous, but it is risky to leave it untreated. Without treatment, depressive episodes tend to become more frequent and more severe.

You describe another common experience: You went back to a treatment that had worked for you before, but now it no longer works. Scientists don't have a good explanation for why this happens. Maybe your circumstances changed. For example, you may have new stresses or losses that you didn't have to deal with the first time.

There are a number of ways to manage this problem:

• You may need a higher dose of antidepressant.
• You may need to switch to a different antidepressant.
• You may need to try a new combination of medications (sometimes it helps to combine drugs that work in different ways or on different brain chemicals).

And don't forget about psychotherapy. If you're not already seeing a therapist, I recommend that you should. The combination of medication and psychotherapy is often more effective than either treatment alone.

We can't cure depression permanently. Treatments for depression are not like the antibiotics we take that get rid of an infection. But treatment can control depression. So, once you've found a treatment that works for you, your doctor will probably recommend that you continue to take it. That's the best way to stave off further episodes.