Starting Prozac Versus Restarting Prozac: Efficacy And Side Effects

Hello and thanks for writing to us!

When it comes to the potential adverse reactions (i.e. side effects) of SSRIs (selective serotonin reuptake inhibitors) like Prozac (fluoxetine), they are well-documented. Potential side effects include:

• Sexual dysfunction (~15-20%)
• Drowsiness (~17%)
• Weight gain (~12%)
• Insomnia (~11%)
• Anxiety (~11%)
• Headache (~10%)
• Gastrointestinal (~10%)

There isn't, unfortunately, much data available regarding the situation you're asking about (i.e. having been on Prozac before and restarting after a period of time, will the side effects you experience be the same?).

Restarting Prozac After Stopping - Efficacy

There have been several studies examining the question of how an individual responds (in terms of efficacy) to reinitiating (i.e. starting again) an antidepressant they have been on before, and the results are mixed.

One study concluded the following:

This study suggests that patients who, after an initial response to fluoxetine [Prozac], relapse upon switching to placebo have a relatively high probability of responding to the reinitiation of fluoxetine treatment

Other studies, however, have noted that it isn't uncommon for prior responders to have a decrease in efficacy. One such study states the following:

Our review suggests that a stable response to antidepressants after reinstatement cannot be assumed in all patients.

The overall point here is that it can be hard to predict if restarting Prozac after stopping it will bring about a positive response. Some may, while others won't (or not as strong as before).

Now, you asked about side effects.

Side Effects Restarting Prozac

All the studies I've seen that involve SSRIs (like Prozac) haven't noted any significant difference in the rate at which side effects occur when comparing initiating of therapy, to restarting therapy after a long period of time.

So, in your situation, having been off Prozac for two years, and restarting now, I wouldn't think you'd be any more or less at risk for experiencing the side effects commonly associated with the drug. Two years is a long time too, and you won't have any of the previous drugs in your system.

My recommendation to you would be to be prepared for the fact that you are most likely at the same risk for side effects as most individuals starting Prozac for the first time. Fortunately, if any do occur, they tend to decrease in severity after a few weeks/months.

Final Words

Lastly, you asked about Klonopin. There is a moderate interaction between it and Prozac.

Prozac can inhibit the metabolism of clonazepam. resulting in increased concentrations. In other words, it may make its effects more pronounced. You may want to start at a low dose of Klonopin when taking with Prozac to see how you respond.

Thanks again for reaching out to us!