Q: I have been taking Prozac for several years (40 mg). Over the last few weeks I have had panic attacks so my doctor has also prescribed Celexa (20 mg). Is it common to take two SSRIs in combination like this?
A: No — it is not common to prescribe two SSRIs at the same time.
First, let's clarify something that could be a little confusing.
SSRIs (selective serotonin reuptake inhibitors) are "antidepressants," but they are also used to treat anxiety, including panic. The principles of SSRI treatment are the same, however, whether you take the medication for anxiety or for depression.
Now back to your question about SSRIs.
Generally, there is no reason to give two different SSRIs at the same time. Instead, most doctors will increase the dose of a single SSRI until you've reached the recommended maximum.
At that point, adding a second SSRI does not make sense. Here are two reasons:
SSRIs are similar and have the same mechanism of action. There is no known advantage to using two at once. It's best to stick with one, because it is simpler and more convenient. It also costs less to get one prescription instead of two.
Drugs interact with one another, sometimes in unpredictable ways. This is usually not a problem, but generally speaking, the fewer you take the better. Since there is little known benefit to combining two SSRIs, it is better not to take two different drugs when one is sufficient.
If you don't feel better at a maximum dose of one SSRI, doctors may recommend switching to another antidepressant or adding a second drug.
If you have no improvement at the maximum dose of an SSRI, your doctor is more likely to switch you to a different medication. Theoretically, the SSRI is giving no benefit, so there is no reason to continue it.
If, however, you get partial relief from the SSRI (but less relief than you need) adding a drug from a different class can help. The second drug, by acting through a different mechanism from SSRIs, may be able to build on the partial good effects of the SSRI.
It's not unusual for a doctor to recommend switching from one SSRI to another. But in that case, it's usually because of subtle differences in side effects. Let's say you have a significant reduction in panic attacks on one SSRI, but you develop intolerable nausea. You might try another SSRI with the hope that you get the same positive response without the stomach distress.
It is possible that there are special circumstances that I'm missing. Your doctor may have a good reason for prescribing these two drugs together. You should ask about the reasons and satisfy yourself that you understand them.
