How Quickly Does Prozac (Fluoxetine) Work?

Medically reviewed by David Snyder, PharmD, BCPP

Prozac is the brand name of the active drug fluoxetine, approved by the Food and Drug Administration (FDA) as a treatment for clinical depression, otherwise known as major depressive disorder (MDD). It belongs to the class of drugs called selective serotonin reuptake inhibitors (SSRIs).

Prozac is also used to treat other mental health conditions in adults and children, such as obsessive-compulsive disorder (OCD), panic disorders, and some eating disorders.

Healthcare providers view Prozac as an effective drug that improves symptoms within one to two weeks of consistent use. However, Prozac does carry a black box warning due to its potential for increased suicidal thinking.

For those facing the conditions mentioned above, having access to reliable medication that can effectively assist in managing their day-to-day symptoms is crucial to productively going about their day and having healthy, stable relationships with others.

Read on for more information regarding the safe and effective use of Prozac, including information regarding its guidelines, storage requirements, and potential for side effects.

Understanding Prozac

The FDA approves Prozac for the treatment and management of the following:

• MDD

• OCD (a mental health condition causing obsessive thoughts and compulsive behaviors)

• Bulimia nervosa (an eating disorder)

• Panic disorder with or without agoraphobia (sudden, unexpected attacks of extreme fear and worry)

Most adults (people 18 and older) can take Prozac for depression, OCD, and bulimia. However, children and adolescents 8 and older can safely take it for MDD.

Furthermore, Prozac is also used as a combinational treatment (treatment that combines two or more therapeutic agents) with Zyprexa (olanzapine) for the following:

• Episodes of depression in people with bipolar I disorder (extreme mood swings that include emotional highs and lows)

• Treatment for depression disorder

• Premenstrual dysphoric disorder (PMDD)

Off-Label Uses

Prozac is also used off-label (the practice of prescribing a drug for a different purpose than what the FDA approved) to treat the following:

• Attention-deficit disorder (ADD), a condition marked by hyperactivity and impulsivity that affects a person's day-to-day life.

• Borderline personality disorder (BPD), a mental health condition involving challenges with mood, relationships, and self-image

• Sleep disorders

• Headaches

• Mental illness

• Post-traumatic stress disorder (PTSD)

• Tourette's syndrome (a nervous system disorder causing sudden twitches, sounds, and movements), obesity, sexual problems, and phobias(fear of things, objects, or places).

How Does Prozac Work?

Prozac belongs to the class of medications called SSRIs. It works by inhibiting the reabsorption of serotonin (a neutral chemical in the brain) and increasing its levels.

The high serotonin levels carry signals between neurons, providing the sensation of happiness and reducing depression disorder.

As mentioned above, Prozac comes with an FDA black box warning about an increased risk of suicide in people with MDD. Young adults, teenagers, and children may experience worsening depression and may be more likely to become suicidal.

Close monitoring and emotional help can ease the symptoms in these people to avoid any harm.

How Quickly Does Prozac Work?

Prozac shows some improvement in sleep, energy, or appetite within one to two weeks. However, a person's depressed mood and lack of interest in daily activities may need up to six to eight weeks to improve fully.

Prozac may take four to five weeks or longer to improve a person's symptoms or achieve therapeutic effects.

However, know that the timing of Prozac's ability to work is not entirely definitive, meaning that various factors may affect how quickly it affects each person.

Such factors include the following:

• Dosing Volume: Symptom relief can be delayed if a dose is too low. In comparison, taking too high an amount might lead to side effects, such as nausea or dizziness.

• Weight: People who are overweight or obese may take longer to experience the effects of Prozac versus those with average body weight.

• Metabolism: Those with slower metabolisms may take longer to feel the effects since their bodies process drugs differently.

Continue to take Prozac even if you feel well. Do not stop taking it without talking to your healthcare provider. Sudden discontinuation of Prozac may cause withdrawal symptoms. 

How Effective Is Prozac?

SSRIs are effective in treating the symptoms of depression. The results from the studies on people with severe depression state that SSRIs are more likely to relieve the symptoms than other antidepressants or those who take a placebo.

In one study, over half of the participants (people 16 to 65 years old) who received 20 milligrams (mg) of Prozac daily for eight weeks showed improved symptoms improved within two weeks.

Furthermore, the cumulative response to Prozac in people of different ages at four and six weeks was 80.2% and 89.5%, respectively.

Available data indicates that improvement from Prozac treatment predominantly occurs within the first two weeks.

More research needs to be done on the exact time-to-effect and risks of Prozac, but current evidence suggests it is an appropriate first-line treatment option.

Dosing Guidelines

Take Prozac exactly as prescribed by your healthcare provider. Do not take it for the conditions other than prescribed.

Prozac is available in the following forms of administration:

• Capsules: 10 mg, 20 mg, or 40 mg IR (immediate release)

• Weekly capsules: 90 mg DR (delayed-release)

For context, know that the delayed-release formulation (90 mg once weekly) is similar to receiving the 20 mg daily variation of Prozac.

Given below is a general overview of the dosing range of Prozac for various indications in adults and children:

The frequency and the dose amount should be reduced when used in people with hepatic impairment (liver problems), older adults, and people with concurrent disease or on multiple concomitant medications.

Your healthcare provider will determine the most suitable dose for you. 

Side Effects & Safety

Prozac is an effective drug when used as prescribed. However, like other SSRI medications, it carries both common and mild and rare and severe side effects.

Therefore, closely monitor yourself or a loved one for the potential emergence of any adverse effects.

If you notice that these or other side effects begin to worsen or do not dissipate, contact your healthcare provider immediately.

Finally, per its black box warning, be acutely aware of the emergence of suicidal thoughts or tendencies.

Common Side Effects

Common side effects associated with the use of Prozac (these side effects will often improve over one week or two) include:

• Headache

• Nausea

• Diarrhea

• Dry mouth

• Increased sweating

• Fatigue

• Insomnia (trouble sleeping)

• Weight loss

However, as a byproduct of using Prozac, sexual side effects, such as problems with orgasm, decreased sex drive or ejaculatory delay, and inability to get or keep an erection, often do not diminish over time.

Severe Side Effects

More rare but severe side effects associated with the use of Prozac include:

• Allergic reactions include symptoms such as rash, urticaria (hives), blisters, itching, swelling of the face, throat, tongue, lips, eyes, hands, feet, ankles, or lower legs, and difficulty breathing or swallowing

• Fever

• Joint pain

• Severe muscle stiffness or twitching

• Hallucinations

• Cardiac arrhythmia (abnormal heart rhythm)

• Fainting

• Seizures

• Abnormal bleeding or bruising

Also, know that Prozac may decrease appetite and cause weight loss in children. Monitor a child's growth carefully. Talk to your child's healthcare provider about the risks of giving Prozac to your child.

Call your healthcare provider right away if anyone taking Prozac experiences any of the following symptoms:

• New or worsening depression

• Thinking, planning, or trying to harm oneself

• Extreme worry

• Panic attacks

• Difficulty falling asleep or staying asleep

• Irritability

• Abnormal excitement or doing things haphazardly without thinking

Call for medical help, and don't wait for these symptoms to disappear or manage yourself.

Who Should Avoid Prozac?

Do not take Prozac:

• If you are allergic to fluoxetine or any other capsule ingredient

• If you also take pimozide or thioridazine

• If you have used a monoamine oxidase inhibitor (MAOI) for 14 consecutive days.

• If you are pregnant or breastfeeding

Generally, you should wait at least 14 days after stopping an MAO inhibitor before you take Prozac. Also, wait at least five weeks after stopping Prozac before you can take thioridazine or an MAOI.

To make sure Prozac is safe for you, tell your healthcare provider if you have ever had:

• Liver problems

• Heart problems, or a history of heart problems in your family

• Kidney disease, including chronic kidney disease (CKD)

• Diabetes (both type 1 and type 2)

• Narrow-angle glaucoma

• Seizures

• Bipolar disorder (manic depression)

• Drug abuse or suicidal thoughts

• Electroconvulsive therapy (ECT)

• Low levels of potassium, magnesium, or sodium in your blood.
  

Potential for Interaction

Prozac may cause drug-drug interaction with other drugs.

Be careful while using the following drugs when taking Prozac:

• MAOIs, such as Marplan (isocarboxazid) or Zyvox (linezolid)

• Medications for anxiety disorders, such as Xanax (alprazolam)

• Antibiotics, such as Zymaxid (gatifloxacin) or Avelox (moxifloxacin)

• Amphetamines, such as Adderall (amphetamine/dextroamphetamine) or Dexedrine (dextroamphetamine)

• Anticoagulants (blood thinners), such as Jantoven (warfarin)

• Antidepressants (mood elevators), such as Norpramin (desipramine), or Pamelor (nortriptyline)

• Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs), such as Advil (ibuprofen) and Aleve (naproxen).

• Insulin or oral medications for diabetes, such as Amaryl (glimepiride) or Glucotrol XL (glipizide)

• Medications for Parkinson's disease, such as Zelapar (selegiline) or Azilect (rasagiline)

• Medications for mental illness, such as Clozaril (clozapine)

• Medications for migraine headaches, such as Relpax (eletriptan) or Rizafilm (rizatriptan)

• Medications for seizures such as Tegretol (carbamazepine) or Dilantin (phenytoin)

• Other SSRIs, such as Celexa (citalopram) or Paxil (paroxetine)

• Serotonin-norepinephrine reuptake inhibitors (SNRI) medications, such as Pristiq (desvenlafaxine) or Cymbalta (duloxetine)

Tell your healthcare provider about all your over-the-counter (OTC) or prescription medicines.

Your healthcare provider may need to change the doses of your medications or monitor you carefully for side effects.

Summary

Depression and anxiety disorders can negatively affect the quality of life. These conditions of despair are becoming more prevalent in Western society across all age demographics, particularly in younger people.

Fortunately, for those clinically diagnosed with mental health conditions, such as MDD, anxiety, or an eating disorder, pharmaceutical treatment options, like Prozac, do exist.

However, Prozac, or other SSRIs, must be used only under professional healthcare supervision due to its potential for increased suicidal thoughts or desires.

Because Prozac takes several weeks to work, dosing guidelines must be followed closely.

Additionally, while on Prozac, closely monitor yourself or a loved one for the emergence of adverse effects, and never be hesitant to ask for guidance from your healthcare provider.

Frequently Asked Questions

How can I safely store Prozac?

Store Prozac tablets in a tightly closed container away from heat and moisture—store at room temperature (between 68 and 77 F).

Keep all medications away from the sight and reach of children and pets. Store Prozac tablets in a tightly closed container away from heat and moisture.

How can I safely dispose of Prozac, if necessary?

Discard unneeded or expired medications, including Prozac, to ensure that pets, children, and others cannot consume them. Do not flush this medication down the toilet or throw it away in the trash.

The best way to dispose of your medication is through a medicine take-back program. Ask your pharmacist or contact your local waste management department in your community.

How common are anxiety disorders in the United States? What about depression?

Depression is more than just feeling down or having a bad day. It may interfere with everyday functioning and affect you very badly if it lasts long.

In general‚ one out of every six adults will have depression at some time.

According to statistics, depression affects nearly 16 million American adults every year. Anxiety disorders often go hand in hand with depression.

Read the original article on Verywell Health.