Could exercise change how much of your antidepressant you need?

Q. Is it possible that, after four months of jogging three times a week for 45 minutes, that the dosage of my antidepressant, sertraline, would need to be adjusted downward because my body is now creating the same antidepressant effect on its own?

A. It's great that you're devoting yourself to regular exercise. There is no question that it is good for your whole body, including your brain. And perhaps you've already read that exercise is helpful for depression. It can lift mood, quell anxiety, improve sleep, increase energy, and enhance self-esteem. There is biological evidence, in fact, that exercise provides some of the same positive effects on the brain that antidepressants do.

But it is not so clear that you can use exercise as a substitute for medication as a depression treatment. It may work out for a few people to make such a switch, but it's not a sure bet at all. It is not like substituting brown sugar for white sugar in a recipe.

In most cases, I would not recommend altering a medication dose, especially if you have suffered moderate or severe depression in the past. Even if you maintain your exercise regimen, there is a risk of relapse when you stop an antidepressant.

As much as we're learning about the biology of depression, our knowledge is not precise enough for us to be able to predict how different treatments will affect a given individual. We do know — from both the biological and environmental point of view — that there are many, many types of depression, and that one treatment does not fit all people. A person who gets better on antidepressant X may experience absolutely no improvement on antidepressant Y.

But let's celebrate the value of exercise for a moment.

Jog long enough and you may get an "endorphin high" that lasts for a short period. Exercise regularly and your brain begins to change for the better. The blood flow and energy supply to nerve cells improve. Those cells get healthier, grow bigger, branch out, and make new connections. New nerve cells are even created, a process called neurogenesis. On brain scans, scientists have found that some parts of the brain involved with managing mood actually get bigger.

Similar brain changes can also be seen after several weeks of taking an antidepressant. Anyone who exercises regularly may therefore be tempted to cut back on an antidepressant dose.

Proceed with caution, however. A lot of biological processes are still invisible to us. Different antidepressants have different mechanisms of action. They create the end result through different biological processes. Thus, a given medication may help in ways that exercise doesn't touch. (The converse is also true: exercise touches things that antidepressants don't.)

It may be that in your case, the antidepressant treatment and the exercise are complementing each other. For example, the antidepressant may be tweaking your motivation centers, providing you the impetus to go out the door and start running.

It sounds like you are feeling helped by both the medication and by the exercise.

Here are some possible scenarios and the way I'd think about them:

• Depression symptoms could return on a lower medication dose.
• If your symptoms were severe before you started antidepressant treatment, your risk is higher than if your symptoms were mild.
• If you are not experiencing any adverse effects from your medication, you may not want to alter the current dose.
• If you are currently experiencing uncomfortable medication side effects, that creates more motivation to reduce the medication dose. But it may also be a good idea to try a different drug.
• Some people simply don't like taking any medication. Take care to consider the merits of that philosophy along with other benefits and risks of changing your treatment.

Take stock of how you feel, and what works and doesn't work about your current treatment. If you're feeling fine, think carefully about what's at stake for you. Make sure that what you seek by reducing the medication dosage has the potential to improve rather than diminish your sense of well being. And most importantly, do not alter the dose of your medication without talking to your doctor first.

Image: © The Good Brigade/Getty Images