How long does Prozac last? (3 important factors)

In this brief article, we are going to answer the question, “How long does Prozac last?”. Prozac (Fluoxetine), is a selective serotonin reuptake inhibitor (SSRI) that can be used for the management of various depressive disorders.

This article will cover how long Fluoxetine stays in your system and what factors can affect this time duration. We will also discuss what side effects can be experienced by Prozac and how to discontinue Prozac safely and effectively.

How long does Prozac last?

Prozac lasts in your body for about 1 to 4 days after oral intake. It has an active metabolite known as norfluoxetine which can stay in the system for 7 to 15 days. Prozac should be used with caution in individuals with hepatic dysfunction (1).

Such a long duration of action of Prozac can be one of the reasons that it is used as a first-line treatment option for many indications. However, this medication needs to be used under continuous monitoring and on the prescription of a healthcare professional.

How long does it take for Prozac to be maximally effective?

Prozac may take 1-2 weeks to start working and managing your depression symptoms like fatigue and restlessness. It can take about 6 to 8 weeks to completely manage a depressed mood. This duration can be different in different individuals. That is why you should give enough time to your antidepressant to work and not leave your treatment midway. On an average patients report that they found Prozac immensely beneficial for their depression after one month of regular use.

Short-term beneficial effects seen with Prozac therapy include managing some of your depressive symptoms like fatigue, insomnia and restlessness. A complete sense of well-being and treatment for depression can take a much longer time and can only be achieved with continuous Prozac use (2,3).

What factors can influence the duration of Prozac in your system?

Different factors can influence the duration of Prozac’s effects in your system. Some of them are as follows (4):

Pharmacokinetics of Prozac

Prozac is well absorbed after oral intake and has good protein binding capacity and volume of distribution. It also has a long elimination half-life, with an even longer half-life of an active metabolite. All this is directly related to the duration of Prozac’s effects on your system (1).

Dosage & treatment duration

Prozac is given as a once-daily dosing, at 20mg/day. This dose is effective in many individuals but sometimes has to be reduced to 10mg/day in people who cannot tolerate the side effects. This reduction in dosage can increase the time taken by Prozac to reach an efficacious plasma concentration. A delayed-release formulation of Fluoxetine (90mg/week) also shows the same duration and efficacy response as the 20mg/day dosing (4).

The treatment of duration also affects the duration of Prozac’s effects in your system. If you are at the start of your treatment, and discontinue Prozac due to any reason, it takes only a few days for the effects of Prozac to disappear from your body but if you have been taking the medication for a longer duration, complete elimination of Prozac can take up to almost one month after the last dose was taken. The active metabolite, norfluoxetine can take even longer to leave the system.

Individual variation and medical factors

Every individual has a different metabolic rate, and this difference can cause Prozac to be absorbed or eliminated differently.

• Hepatic dysfunction – People with hepatic dysfunction, eliminate Prozac slower than individuals with normal hepatic function. This delayed elimination can cause the medication to stay longer in your system. 
• Pregnancy & Breastfeeding – Pregnant and breastfeeding women are normally given lower doses of Prozac than normal to avoid high concentrations in their system which can harm the baby.
• Pediatric patients – Pediatric patients do not have fully developed hepatic function, which can influence the duration of Prozac’s effects in their system. Younger children tend to have suicidal ideas due to the increased effect of Prozac on their system.

Drug interactions

Some medications can act synergetically with Prozac, by increasing its serotonergic effect. Monoamine oxidase inhibitors (MAOIs) are of value in this regard. Fluoxetine should be discontinued 5 weeks before MAOI therapy to avoid excessive effects. Ibuprofen decreases the effectiveness of Prozac, hence decreasing its effects on your system.

Time of intake

The time of intake of medication does not affect the duration of Prozac’s effects on your system. There has been no recorded study until now that states otherwise.

How to taper off and discontinue Prozac?

Tapering off and discontinuing Prozac has to be closely monitored by your healthcare provider. Prozac is known to cause withdrawal syndrome. This can happen if the dose of Prozac is lowered too quickly, and the plasma concentrations see an abrupt decrease. Withdrawal symptoms include nausea, flu-like illness, restlessness, headache and insomnia. These symptoms can be resolved if Prozac is discontinued gradually and at a steady pace. 

If you are on Prozac therapy for any depressive condition, and you need to stop or change your medication your doctor will do it throughout a few weeks. It still may take 4 to 5 weeks after cessation of Prozac therapy to fully eliminate the medication from your system so you may still see some effects. Make sure to follow your doctor’s treatment plan to avoid withdrawal symptoms or complications.

What are the possible side effects of Prozac therapy?

Most side effects of Prozac therapy are dose and time-dependent. They normally occur at the start of therapy and disappear when you get used to the medication, or on adjusting the dosage. Some common side effects are insomnia, anorexia, anxiety, dry mouth, headache, weight gain or loss, tremors and yawning.

If you experience any of these side effects your healthcare provider will most likely wait for a couple of weeks for the effects to subside. Most side effects will only be there for a short duration but if waiting it out doesn’t work then your doctor may alter your treatment.

Some side effects are rare and can be linked to the increased duration of Prozac in your system. Serotonin syndrome is one such side effect which can occur if Prozac stays in your system longer than needed. The symptoms of serotonin syndrome are muscle rigidity or twitching muscles, high blood pressure, agitation, dilated pupils and confusion. If you experience effects like the serotonin syndrome your doctor will discontinue treatment and prescribe you medication that counteracts the effects of Prozac.

Conclusion

In this article, we answered the question “How long does Prozac last?”. We also discussed what factors influence the duration of Prozac’s effects and elimination time from the system and how to discontinue Prozac safely and effectively.

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