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The Best Time to Take Prozac

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A short introduction to Prozac

Prozac is one of the most frequently prescribed medications in the United States, coming in at #4 on the list of antidepressant medications, which are themselves the most frequently prescribed of all meds. Nearly twelve million scripts for Prozac were written in 2021, and it looks like its numbers and its overall ranking will be even higher for the current year. Whether it is best to take Prozac first thing in the morning, or early in the evening has raised a lot of debate amongst both the medical fraternity and patients – there are even quora forums that discuss the issue! To better understand why there is even some discussion of what should be a standard protocol, let’s look a bit deeper into the subject. We will look at what Prozac is meant to be doing, how it works, and why the time of day it’s taken may be an issue among people who have been prescribed the medication.

What is the purpose of Prozac?

Prozac (generic name: fluoxetine) is prescribed as a treatment for people exhibiting symptoms of clinical depression, panic attacks, OCD (obsessive-compulsive disorder), bulimia, and extreme mood swings. It belongs to the class of selective serotonin reuptake inhibitors (SSRIs) antidepressants.

How does Prozac function?

Serotonin is a neurotransmitter – a chemical essential in transmitting signals inside the brain and along nerve paths to muscles and organs. The level of serotonin regulates mood, sleep, appetite, and digestion. Low levels will aggravate any feelings of anxiety, anger and depression. For people suffering from mood swings and depression, boosting serotonin levels can significantly reduce these feelings. Selective serotonin reuptake inhibitors slow down the reabsorption of serotonin during neurotransmission, allowing it to remain in the nerve cells for reuse. One of the most interesting facts about SSRIs, which was only discovered by recent research long after doctors had started prescribing them for patients with clinical depression, is that they don’t just increase serotonin levels.  Researchers found that for serotonin to effectively lower anxiety levels, SSRIs should be taken in daily doses for at least a couple of weeks. Its effect is to eventually cause changes in the structure of neurons (known as neuroplasticity). Neurons adapt to increased serotonin levels, grow new dendrites (branches connecting to other nerves) and change the number of serotonin receptors throughout the brain. The higher serotonin levels boosted by SSRIs increase the brain’s capacity to restructure itself, making it more amenable to adaptation and remodeling. This is why you are usually advised to stick to the prescribed dosage routines for at least a few months. You may not start to feel the benefits immediately. The best effects of Prozac will start to kick in once the process of neuroplasticity has had an opportunity to work.

How does Prozac affect waking and sleeping?

The circadian rhythm (sleep-wake cycle) is regulated by the tiny pineal gland in the brain that reacts to ambient light levels. It will translate these signals and control the production of melatonin, a hormone that makes you feel sleepy. It functions as well to control levels of serotonin and dopamine. When light is brighter, it will produce more dopamine and reduce melatonin levels. Dopamine keeps you awake. Drugs that increase dopamine levels, such as cocaine, nicotine, caffeine and amphetamines increase alertness. Serotonin has a more complex role in the circadian cycle. While it induces drowsiness, it can also stop you from falling asleep or cause restless and unsatisfactory sleep. The main difference comes from where in the brain it comes from and the type of receptor it binds to. While serotonin seems to be able to both induce sleepiness and keep you up, it’s a chemical precursor to melatonin, the primary hormone involved in sleep. 

What difference does it make whether Prozac is taken in the morning or night?

There are no hard-and-fast rules. The main decider will be your specific reaction to the drug, especially the side effects it has on you. Prozac is sometimes best when taken in the morning due to its potential side effects. Here are a few to consider.
  • Insomnia or restless sleep
  • Urinary problems (mostly in young adults)
  • Sexual problems (low libido, erectile dysfunction)
In the case of the following common side effects, it may be preferable to take the dosage at night. In this case, it will have less impact on you, or you will be in a more amenable environment:
  • Nausea
  • Loss of appetite
  • Headaches
  • Diarrhea
  • Feeling tired or weak
  • Drowsiness, loss of concentration


As we said, every person will respond differently to Prozac. In the end, the decision to take it in the morning or evening will be one you should take, after consultation with your doctor, based mainly on your own experience with it. What is essential for everyone is to be consistent with whichever routine you decide on. Try to keep the time of day at which you take Prozac the same every day. If you miss taking it, try to make up for the missed dose within a few hours, but don’t double-dose the following day. You should begin to see the best improvements in your levels of anxiety and depression after a few weeks. Stick to the plan even if you do not see the benefits immediately.
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