Prozac for anxiety: How it works and what to expect

What is Prozac?

Prozac (fluoxetine) is a selective serotonin reuptake inhibitor (SSRI) and one of the first SSRIs ever developed. It works by increasing the amount of serotonin available in the brain, which is a neurotransmitter involved in emotion regulation.

Prozac is FDA approved to treat major depressive disorder, obsessive-compulsive disorder (OCD), panic disorder, bulimia nervosa, and premenstrual dysphoric disorder. It’s also often prescribed off-label for other conditions, including other types of anxiety disorders.

How does Prozac work for anxiety?

As mentioned above, Prozac increases the amount of serotonin available in the brain. But how exactly SSRIs improve anxiety isn’t completely understood, and it’s probably more complicated than simply having more serotonin around.

SSRIs are thought to affect brain plasticity, which is the brain’s ability to adapt to new information. For anxiety specifically, some researchers think that, by raising levels of serotonin, SSRIs may calm the amygdala, which is responsible for activating the fear response.

Unlike fast-acting anxiety medications like benzodiazepines, Prozac does not provide immediate relief. Benzodiazepines can reduce anxiety within hours, while Prozac often takes several weeks or more to feel the full effects.

How effective is Prozac for anxiety?

Research on Prozac’s effectiveness for anxiety varies depending on the anxiety disorder. But efficacy can also depend on your individual response to the medication, which is something Kate Hanselman, PMHNP, VP Clinical Psychiatry at Thriveworks, sees in her practice often.

When deciding which medication to try first, Hanselman says, “I’m most likely to start with a medication they’ve tried in the past if it was effective, or a medication that was helpful for a relative, if that information is available.” Even when Prozac may not have been shown to be effective in trials for a particular anxiety disorder, Hanselman notes it can still be worth a try, because each person’s response is unique.

Another consideration she weighs is adherence. For Hanselman, “Prozac can be particularly helpful for patients who sometimes forget to take their medication, because it sticks around in your body for longer than other medications in the same class.”

Here’s what the research says about Prozac’s effectiveness for different types of anxiety:

Panic disorder

Of all the anxiety disorders, Prozac has the strongest evidence for treating panic disorder. It is FDA approved for panic disorder based on two clinical studies, according to the drug’s prescribing information.

In one study, 42 percent of people taking Prozac were completely free of panic attacks by the end of the study, compared with 28 percent taking a placebo. In the second study, 62 percent of people taking Prozac had no panic attacks at the end of 12 weeks, compared with 44 percent taking a placebo.

Generalized anxiety disorder (GAD)

Prozac isn’t FDA approved to treat generalized anxiety disorder (GAD), but it can still be prescribed off-label. While it can be effective for some people, the evidence isn’t as strong as it is with panic disorder.

A large network meta-analysis of 41 randomized trials compared a variety of medications for treating GAD in adults and found that fluoxetine wasn’t clearly better than the placebo. This was based on the Hamilton Anxiety Scale, a standard measure of anxiety symptoms.

The evidence is more encouraging in children and teens. In a 12-week randomized trial of 74 youth with GAD, social anxiety disorder, and/or separation anxiety disorder, about 67 percent of those with GAD who took fluoxetine improved, compared with 36 percent who took the placebo. Most participants had more than one anxiety disorder, so the study wasn’t limited to GAD alone. Another review of pediatric GAD treatment counts fluoxetine among the better-studied options for young people. But that evidence is specific to children and teens and doesn’t necessarily apply to adults.

This doesn’t mean Prozac won’t work for adult anxiety. But it does mean its track record is thinner than what we have for panic disorder. And since there are other medications FDA approved for GAD (like escitalopram and duloxetine), Prozac might not be your provider’s first choice.

Social anxiety disorder

Prozac can also be used off-label for social anxiety disorder, but the evidence is mixed, and the medication is not as well-studied as other FDA-approved options.

One large study involving nearly 300 adults with social anxiety found that about half of those taking fluoxetine responded after 14 weeks compared with about one-third taking placebo. This was about the same response rate as cognitive behavioral therapy (CBT) or a combination of fluoxetine and cognitive behavioral therapy. But another smaller study of 60 people with social phobia did not find that fluoxetine was better than placebo.

Common risks and side effects of Prozac

Like other SSRIs, Prozac can cause side effects such as nausea, headache, sexual problems, sleepiness, insomnia, sweating, and changes in appetite or weight. In real-world survey data of about 700 people taking SSRIs, sexual side effects, sleepiness, and weight gain were among the most commonly reported problems.

That said, there are a few ways that Prozac differs from other SSRIs:

• It may feel more activating. Prozac can be slightly more activating than some other antidepressants. In a meta-analysis of randomized trials, activating side effects such as insomnia, agitation, tremor, and anxiety were significantly more common with fluoxetine. In practice, that means some people may initially feel more restless, energized, or “wired” before their anxiety starts to improve.
• It may be less likely to cause weight gain than some other SSRIs. Although it can cause weight gain, fluoxetine has also been associated with weight loss, particularly early in treatment, whereas most other SSRIs are more often associated with weight gain.
• Withdrawal symptoms are less common. Prozac stays in the body longer than any other antidepressant. That appears to reduce the risk of discontinuation symptoms compared with other SSRIs. That also means that missed doses are less likely to cause withdrawal symptoms. But this depends on each person’s situation and the dose, so it’s important not to stop taking the medication without first speaking with your provider, says Hanselman.
• Drug interactions are worth paying attention to. Fluoxetine affects liver enzymes that break down other medications. So it can come with more drug interactions, including tamoxifen, metoprolol, and some antipsychotics.

Rare but serious risks include serotonin syndrome, abnormal bleeding, low sodium levels, seizures, and serious allergic reactions. Like other SSRIs, Prozac also has a boxed warning about an increased risk of suicidal thoughts and behaviors in children, adolescents, and young adults.

What to expect when taking Prozac for anxiety

Prozac is usually taken once daily, in the morning, so that it doesn’t interfere with your sleep. Doses over 20 mg can be split into two doses, with one taken in the morning and one taken around noon. Taking it at roughly the same time each day can also make it easier to remember.

When you first start Prozac, side effects may come before you notice much improvement in anxiety symptoms. Fluoxetine can cause nervousness, restlessness, anxiety, or trouble sleeping, and research on fluoxetine has found that these activating effects tend to appear most often early in treatment and become less common over time.

According to Hanselman, “it’s unlikely to worsen actual anxiety, but people often experience irritability and activation as symptoms of anxiety, so the side effect burden can mimic those symptoms.” From Hanselman’s experience, how activating it is really depends on the person. For some, it could feel like having had an extra cup of coffee. For others, it can be uncomfortable enough to have a discussion about trying a different medication.

When Prozac starts working, you’ll typically notice a gradual improvement, rather than a sudden jump on a particular day. In a small study of 16 children and teens with anxiety disorders taking fluoxetine, improvement occurred after about five weeks on average. Another study in people living with depression suggests that some people who eventually respond to fluoxetine begin improving within the first few weeks. But anxiety tends to respond more slowly to SSRIs like Prozac than depression.

The important thing is to be consistent and give the medication time, even if you don’t feel better at first. As treatment continues, your provider may adjust the dose depending on how well it is working and how you tolerate it. If your anxiety becomes worse, you experience bothersome side effects, or several weeks go by and you still don’t feel any different, that’s a good time to check in with your provider.

Frequently asked questions (FAQs)

Is Prozac FDA approved for anxiety?

Yes, but only for panic disorder. Prozac is used off-label for other types of anxiety disorders, such as generalized anxiety disorder and social anxiety disorder.

Who should not take Prozac?

Before starting Prozac, tell your provider if you have bipolar disorder or a history of mania, seizures, certain heart rhythm problems, or narrow-angle glaucoma. Prozac can worsen or complicate these conditions, and your provider may need to consider another treatment or monitor you more closely.

Prozac interacts with other medications, including tamoxifen, metoprolol, and some antipsychotics. Be sure your provider has a full list of your medications.

Is Prozac a good first choice for anxiety?

Prozac is a good first-choice treatment for panic disorder. For other types of anxiety, it’s not usually the first choice, but it can be used off-label. Work with your provider to find the right medication for you.

Can Prozac make my anxiety worse at first?

Yes, for some people. Prozac can be activating, especially in the first few weeks. So anxiety, nervousness, and insomnia are all possible. This usually gets better over time, but tell your provider if it gets worse or becomes severe.

How long does Prozac take to work for anxiety?

It can take at least four weeks or longer before you feel the full benefits of the medication. You may notice some benefits before that, though. Give the medication time to start working, and don’t stop taking it without talking to your provider first.

Is Prozac addictive or habit-forming?

No. Prozac isn’t addictive or habit-forming, and it’s not a controlled substance. It’s also less likely than other antidepressants to cause discontinuation syndrome when you’re tapering off of it. That said, talk to your provider first before stopping the medication.

Can I take Prozac long term?

Yes. It’s common to take Prozac long term when it’s helping. Your provider will periodically check in with you to be sure it’s still the right fit for you.

Can you overdose on Prozac?

Yes, but it’s rare. Accidentally taking an extra dose is unlikely to lead to serious side effects. Overdosing is more common if you mix Prozac with alcohol or other interacting medications or supplements. If you or someone else may have taken too much Prozac, contact Poison Control at 1-800-222-1222.