Side effects from Prozac (fluoxetine) are relatively common, especially when first starting to take the medication or when increasing your dose. The likelihood of side effects occurring varies by individual and by the dose you are taking. The side effects are generally mild and self-limiting however. In most cases, side effects tend to subside in a few weeks.

Below, we list the common side effects of Prozac (fluoxetine), especially when starting or increasing you dose and discuss them in detail.

Prozac (Fluoxetine) Side Effects


The most common side effects of Prozac relate to the GI tract. They include:

  • Nausea
  • Vomiting
  • Diarrhea

The incidence of these side effects tends to increase with higher doses. Therefore, it is generally recommended to start at a low dose of 10 mg to 20 mg and slowly taper to the effective dose over a period of a few weeks. If they do occur, they generally decrease over a period of a few weeks.


Prozac can cause insomnia or exacerbate present conditions that make it difficult to fall asleep. Sometimes, additional medications to help combat insomnia may be used such as melatonin if sleep problems persist after using Prozac for at least a few weeks.

Sexual Side Effects

Sexual side effects are relatively common in those taking Prozac and can include:

  • Erectile dysfunction
  • Loss  of ejaculatory function in men
  • Decrease of libido
  • Anorgasmia (absence of orgasm)

If sexual side effects occur, the first step is to rule out any conflicting medical (or non-medical) condition. If the sexual effects are related to Prozac and do not subside after a few weeks of therapy, use of additional medication to help with specific symptoms may be justified (e.g. Viagra, Cialis). For females, switching to an anti-depressant in a different class (such as Wellbutrin) may be considered.

Neurologic Effects

Initiating Prozac is associated with an increase in migraine headaches while simply increasing your dose is typically not. These side effects tend to subside in a few weeks if they do occur. Prozac can actually be used to prevent migraine headaches with the caveat of knowing they may initially exacerbate the condition.

Weight Changes

While SSRI medications are associated with both weight gain and weight loss, Prozac specifically is associated with weight loss when treatment is initiated or the dose is increased although the effects generally normalize once you have been taking the same dose for a long period of time.


The above side effects are the most common experienced when starting or increasing your dose of Prozac but is by no means comprehensive. If side effects do occur, they tend to be mild and self-limiting. If they don't subside after a few weeks of starting or increasing your dose of Prozac, be sure to speak with your doctor.