Issac Thorne

Last Updated January 9, 2022

Trying to determine an appropriate phenibut dosage for your research? Then you're in the perfect place.

Phenibut has been around since the 1960s, but it has only recently caught the attention of nootropic researchers outside of Eastern Europe. There’s solid preliminary evidence that phenibut can reduce anxiety in social situations, boost mood, aid sleep, and lead to overall cognitive enhancement.

But how can it be used safely?

This article will give you an overview of prevalent phenibut dosing guidelines, including for research on anxiety, sleep, and even for microdosing.

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What Is Phenibut?

Let’s start with the basics. What actually is phenibut?

Phenibut (β‐phenyl‐γ‐aminobutyric acid HCl) is a neuropsychotropic drug, which means that it has an effect on the nervous system [1].

xPhenibut is usually taken orally as a tablet, or as a powder or salt dissolved in water. In countries where it is available as a medication, phenibut is sold under several trade names including Anvifen, Fenibut, and Noofen.

It’s sometimes referred to as a “tranquilizer” drug [1], but not because it’s actually used as a tranquilizer. The name refers to the fact that it depresses the central nervous system.

Phenibut has the effect of depressing some parts of the brain that are responsible for higher-order thinking, similar to alcohol. These are the parts of your brain that, when they’re overly excited, make one feel stressed and worried. By calming down these parts of the brain, phenibut can help reduce worry and anxiety. It may also help research subjects get better, more restful sleep [1].

While it has some similar effects to alcohol, there are some important differences: phenibut is not known to come with uncomfortable, “drunk”-like symptoms or foggy thinking. Indeed, it is often classified as a “nootropic,” meaning it has the potential to produce cognitive-enhancing effects.

How does phenibut work?

Phenibut is chemically similar to γ-aminobutyric acid, also called GABA, which is a neurotransmitter that is found in your brain and nervous system. Due to its similarity to GABA, phenibut can bind to the GABA receptors and produce the same effects as GABA itself. Specifically, phenibut is an agonist of the GABAB receptor, which sends slow-acting inhibitory messages.

GABA is a neurotransmitter that inhibits activity. If you think of your neurons like light switches, GABA is responsible for turning off the lights after other neurotransmitters turn them on. It plays an important role in reducing neuronal excitability in the nervous system.

Because phenibut binds to the GABA receptors, it also has a role in inhibiting neural functions and reducing excitability. That is why, in countries where it’s used as a medication, it’s prescribed to treat or relieve conditions like anxiety, insomnia, PTSD, and alcohol use disorder [1].

Also, at low levels, phenibut has been found to upregulate dopamine levels, which may result in a pleasurable, euphoric feeling.

In the United States, phenibut has not been approved for any use. It is classified as a “New Drug” under the U.S. Federal Food, Drug and Cosmetic Act (FD&C Act). Because phenibut is an unregulated compound, it is available for research use, but it should not be used outside of a research context.


Phenibut Side Effects and Safety

In the countries where it’s prescribed, phenibut is generally regarded as well-tolerated [1]. That said, researchers and their test subjects should be keenly aware of phenibut side effects, including the potential effects of withdrawal and overdose.

Phenibut side effects

Here are some of the more common and less severe side effects of phenibut [2]:

  • Drowsiness
  • Nausea
  • Irritability
  • Headache
  • Sedation

More severe side effects can occur in individuals that take phenibut at high doses. These include:

  • Motor incoordination
  • Hangover-like symptoms
  • Loss of balance

Like many substances, some people may experience allergic reactions to phenibut. These can include skin rash and itching. Subjects who experience allergic reactions or side effects should immediately stop use, and seek medical attention.

Interaction effects

Since phenibut is a central nervous system (CNS) depressant, it can interact with other substances that influence the central nervous system, including alcohol, anxiolytics (medication for anxiety), antipsychotic medications, sedatives, opioids, and anticonvulsants.

It can make any of these drugs stronger or last longer than normal.

Individuals who use any medication or drug that can impact the CNS should refrain from participating in phenibut research. Researchers should disclose all available information about possible interaction effects to their participants, specifically instructing them to refrain from using alcohol for the duration of the study.

Phenibut withdrawal effects

Note that test subjects may develop tolerance to and dependence on phenibut [3]. Phenibut can be addictive, which is especially likely for individuals who consume phenibut regularly over a long period of time.

With repeated use, an individual’s body can get accustomed to phenibut and stop producing its own GABA. The body does this to balance out GABA level: when there is already enough phenibut in the system, the body produces less GABA. Then, when the subject discontinues phenibut use, the body takes awhile to restart its GABA production, so there is some time when there are low levels of the neurotransmitter.

This can lead to withdrawal symptoms, which include [3, 4]:

  • Rebound anxiety
  • Anger
  • Agitation
  • Irritability
  • Insomnia
  • Auditory and visual hallucinations
  • Psychosis

To avoid withdrawal effects, research participants should not take phenibut over a long period of time or regularly [5, 6, 7, 8].

Researchers should design their studies to ensure that subjects minimize long-term exposure. Precautions can include:

  • Ensuring that test subjects not take phenibut more than two times in a single week.
  • Ensuring that test subjects cycle off phenibut for four to eight weeks if a research study persists over the medium or long term.

Phenibut Dosage Guide | The Basics

So what dosage of phenibut should you use for your research study? Here’s what you need to know.

First, phenibut generally comes in two forms: phenibut HCL and phenibut FAA.

There are slight differences between the two:

  • Phenibut HCL is a salt. This is typically how phenibut comes. It’s made from taking the phenibut free amino acid and getting it to react with hydrochloric acid, making it an ionic salt. Because it’s ionic, it will dissolve in water, making it easy for your test subjects to consume in a drink. Phenibut HCL sometimes also comes in capsule form. Your test subjects may prefer to consume phenibut HCL with citrus juice to remove any bitter taste.
  • Phenibut FAA is a free-form amino acid. This version of phenibut is not as dissolvable as the HCL version, so it’s not as easy to consume by drinking. Instead of putting phenibut FAA in water, your test subjects may wish to take it by placing it under the tongue. It takes several minutes to be absorbed in this fashion. Phenibut FAA can also be consumed in pill form. Compared to phenibut HCL, phenibut FAA tends to be more expensive.

Both phenibut HCL and phenibut FAA are the same chemical substance. Phenibut FAA typically has a bit more of the chemical by weight just because of how it’s produced. This means that subjects using FAA can take a lower dose compared to HCL.

See below for more detailed guidance on how you may wish to calculate research doses using each of these two forms.

Great, so what is an appropriate phenibut dose?

How much phenibut a test subject should take in a dose depends on a few factors:

  • The subject’s body size. All other things equal, larger people need more phenibut feel the same effects.
  • The subject’s age. Older people should generally take less than younger people.
  • The subject’s health. In general, consider excluding individuals with chronic conditions, liver issues, or kidney issues from phenibut research out of an abundance of caution.
  • The effect you are looking to observe. See below for more guidance on this.

Because there are so many factors that can influence dosing, it’s difficult to provide concrete dosing suggestions for nootropic research.

We have included some potential dosing strategies below. We’ve developed these by reviewing the existing research and seeing what other nootropic researchers have done.

Generally, it’s prudent to start participants on very low doses and only increase gradually if there do not seem to be adverse effects.

For example, you may consider starting test subjects off with a small dose of just 250 mg. If they tolerate that amount, you may choose to increase the dosing slowly, in 50 mg increments, to find the ideal dose.

First-time phenibut researchers should recall there may be a lag between when the test subject takes phenibut and when you can observe its effect. It is also encouraged to take phenibut at least one hour before eating. It will work faster if consumed on an empty stomach.

How long can phenibut last?

The half-life of phenibut was found to be 5.3 hours. That means that after about 5 hours, a test subject’s body will have metabolized half of it. By that time, the subject may stop feeling its effects.

Of course, the length of time an individual can feel the effects depends on factors including their body chemistry and the size of the dose. Some individuals have reported feeling the effects of phenibut for up to 24 hours [5].


Phenibut HCL Dosing Guidelines

Phenibut HCL is an ionic salt that dissolves easily in water or other beverages. This is a common way for test subjects to consume phenibut.

Phenibut HCL typically has less phenibut by mass than the FAA form, which means that your doses might be slightly higher compared to FAA.

Researchers commonly apply the following phenibut HCL dosage for first-time users:

  • 350mg to 500mg/day
  • split into 1 to 3 doses
  • taken at least one hour before food (i.e. on an empty stomach)

This dose is on the low end of therapeutic doses used in clinical research. Phenibut at this dosage is generally well-tolerated [9].

Phenibut FAA Dosing Guidelines

Phenibut FAA does not mix well with liquids, so your test subjects may not want to dissolve in a drink. Instead, they can put it under their tongue and wait for it to absorb.

Another method of administration is to fold phenibut FAA up in dissolvable paper and swallow it. Putting it in capsules is another popular method.

Because the phenibut FAA dosage will contain more total phenibut compared to the HCL form, your test subjects may need less of it to feel the same effect. 250 mg of phenibut FAA is roughly the same as 400 mg of phenibut HCL. Accordingly, specify a smaller dose if you’re using phenibut FAA.

Researchers commonly apply the following phenibut FAA dosage for first-time users:

  • 250mg to 350mg/day
  • split into 1 to 3 doses
  • taken at least one hour before food (i.e. on an empty stomach).

Again, this dose is on the low end of therapeutic doses used in research and is generally well-tolerated [9].

Phenibut Dosage for Anxiety

To study the effects of phenibut in social situations or as an anxiolytic, first-time users may be given:

  • 250mg to 350mg/day
  • split into 1 to 3 doses
  • taken at least one hour before food (i.e. on an empty stomach).

This phenibut dosage for anxiety may help subjects experience a general sense of calmness and improved mood, especially in situations that would otherwise cause anxiety. It’s on the low end of the dosing spectrum in existing phenibut research [9].

Phenibut Dosage for Sleep

You may wish to increase the dose to study phenibut sleep benefits. An appropriate phenibut dosage for sleep might look like this:

  • 500mg to 750mg/day
  • split into 1 to 3 doses
  • taken at least one hour before food

This slightly higher dose may give a boost to mood and reduce anxiety, but it may also cause an observable improvement in sleep. Again, this is within the typical dosing range used in phenibut research [9].

Microdosing Phenibut?

Some test subjects have reported that phenibut can produce a positive effect in even very small doses. In addition, the purported nootropic effects of phenibut typically happen at small doses, less than 20 mg per kilogram of body weight [6].

We’re not aware of published research using this dosing level, so it would make for an original study. The very low dose also minimizes risks to safety.

If you’re interested in using a microdose for your study, you may try the following guidelines:

  • 50mg to 100mg/day
  • 1 total dose
  • Taken at least one hour before food

You may also choose this dosing regimen if you’re starting out a research study and want to see how your test subjects react to it.


Lethal Dosage?

Phenibut is generally considered safe. One systematic review of phenibut case studies and clinical research concludes, “The current systematic review provides evidence that, at therapeutic doses, phenibut is safe and well tolerated with minor adverse effects” [9].

That said, in the United States, there has been at least one death reported from a phenibut-only exposure [10]. While we are not aware of the circumstances of that case, it does show that phenibut can be lethal.

Apart from death, there are several uncomfortable effects associated with taking an excessive phenibut dose, including:

  • Severe drowsiness
  • Nausea
  • Vomiting
  • Lowered blood pressure

Individuals that have overdosed also may experience short-term changes in consciousness or state, including lethargy, agitation, delirium, reduced consciousness, or even unconsciousness.

Per the recommended dosing guidelines in Russia, test subjects are advised to not exceed 750 milligrams per dose or 2.5 grams per day. Unless it’s used to treat or relieve a condition under medical supervision, phenibut should also not be used more than two times per week.

And to reiterate, it is vital that test subjects NOT mix phenibut with alcohol or benzodiazepines. Using them together may increase the likelihood of overdose and associated symptoms.

Buy Phenibut Online | 2022 Guide

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Phenibut Dosing | The Verdict

Phenibut is an exciting research nootropic that may help individuals feel relaxed, less stressed, and more sociable.

When conducting studies, phenibut researchers are advised to start subjects on a low dose. The following guidelines may help mitigate or prevent side effects for research participants:

  • Not to be used with other depressants like alcohol
  • No more than 750 mg in a single dose
  • No more than 2.5 g/day
  • Used no more than twice per week
  • Implement cycling protocol to avoid the development of tolerance/dependence

These dosage guidelines are general in nature; researchers should carefully design their studies based on the outcomes sought and subjects’ individual characteristics.



  1. Lapin I. (2001). Phenibut (beta-phenyl-GABA): a tranquilizer and nootropic drug. CNS drug reviews, 7(4), 471–481. doi:10.1111/j.1527-3458.2001.tb00211.x
  2. Cheung, J. & Penn, J. (2018). Weekly dose: Phenibut. The Conversation.
  3. Ahuja, T., Mgbako, O., Katzman, C., & Grossman, A. (2018). Phenibut (β-Phenyl-γ-aminobutyric Acid) Dependence and Management of Withdrawal: Emerging Nootropics of Abuse. Case reports in psychiatry, 2018. doi:10.1155/2018/9864285
  4. Högberg, L., Szabó, I., & Ruusa, J. (2013). Psychotic symptoms during Phenibut (beta-phenyl-gamma-aminobutyric acid) withdrawal. Journal of Substance Use, 18(4), 335-338.
  5. Owen, D. R., Wood, D. M., Archer, J. R., & Dargan, P. I. (2016). Phenibut (4‐amino‐3‐phenyl‐butyric acid): Availability, prevalence of use, desired effects and acute toxicity. Drug and alcohol review, 35(5), 591-596.
  6. Zheng, K. H., Khan, A., & Espiridion, E. D. (2019). Phenibut Addiction in a Patient with Substance Use Disorder. Cureus, 11(7).
  7. Samokhvalov, A. V., Paton-Gay, C. L., Balchand, K., & Rehm, J. (2013). Phenibut dependence. Case Reports, 2013, bcr2012008381.
  8. Jouney, E. A. (2019). Phenibut (β-Phenyl-γ-Aminobutyric Acid): An easily obtainable “dietary supplement” with propensities for physical dependence and addiction. Current Psychiatry Reports, 21(4), 23.
  9. Kupats, E., Vrublevska, J., Zvejniece, B., Vavers, E., Stelfa, G., Zvejniece, L., & Dambrova, M. (2020). Safety and tolerability of the anxiolytic and nootropic drug phenibut: a systematic review of clinical trials and case reports. Pharmacopsychiatry. Pharmacopsychiatry, 53(05), 201-208
  10. CDC (2020). Notes from the Field: Phenibut Exposures Reported to Poison Centers — United States, 2009–2019.

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