What to Know About Phenibut Capsules: Phenibut Addiction & Side Effects

Last Updated: July 5, 2021

Authored by Roger Weiss, MD

Reviewed by Michael Espelin APRN

Phenibut is a central nervous system depressant created in Russia to treat anxiety, insomnia, and post-traumatic stress disorder. Its use as a medication is not approved in the USA, so it can be bought only as a supplement. As its use is not regulated, many users purchase it to self-medicate or experience the drug’s cognitive-enhancing properties. Although Phenibut addiction is rare, the drug can still be harmful and cause physical dependence and withdrawal. Learn more about Phenibut capsules, their side effects, interactions, and addiction signs.

What Is Phenibut?

In the 1960s, scientists in the Soviet Union notoriously created the “designer drug” commonly known as Phenibut or Fenibut. It gained more popularity after the rumor that Russian astronauts used it to increase their cognitive powers and keep themselves more relaxed in space.

Fenibut is a neuropsychotropic drug approved in Russia to treat a range of disorders. It is classified as a nootropic, meaning it can boost brain performance, memory, and cognitive function.

The chemical structure of this Phenibut supplement is exceptionally similar to GABA – gamma-Aminobutyric acid – the primary inhibitory neurotransmitter in the human brain. It is a synthetic form of GABA. At low doses, the drug also increases the brain’s dopamine concentration, leading to improved mood and better focus.

The drug is present in two forms: Phenibut HCL and Phenibut FAA.

Phenibut HCL

The drug is delivered as a hydrochloride salt. The manufacturing process includes taking the free amino acid form and reacting it with hydrochloric acid. It is the most common and often considered as the best Fenibut variety.

Phenibut FAA

FAA is the Free Amino Acid form of the substance. Less common than the HCL version. When comparing HCL vs. FAA pros and cons, the reason for Fenibut HCL to be the more dominant and popular form is that it is more stable, convenient, and affordable. Phenibut FAA, on the other hand, is more expensive and rarer. Due to its free amino acid form, it can be directly absorbed into the bloodstream and give fast desired effects.

There are currently no legal restrictions for using, selling, or distributing Phenibut capsules in the USA. However, even though many people in the US use supplements such as fenibut that has gained the nickname “wonder drug” due to its supposed effectiveness, it is currently not approved by the FDA. It is also not prescribed for medicinal purposes. Therefore, all Fenibut supplements and related products arrive at the US market mostly through e-commerce websites. Moreover, FDA has stated that Fenibut doesn’t even fall into the category of dietary supplements, and has even issued warnings to companies, whose dietary supplements contain it.

Gavel on court room table.

It is often considered a potentially dangerous substance by the medical community in the US due to its addictive nature. While relatively rare, a few overdose incidents of this substance have made the physicians warn potential users about their tolerance levels.

Causes Of Phenibut Abuse

Perhaps the most common use of Phenibut supplement is as an enhancer of cognitive abilities. There are not many products in the market that deliver both relaxation and stimulant properties simultaneously, especially at the same level of intensity that Fenibut does. The effect begins when the drug binds to the GABA receptors in the brain. This is vital to the medication’s function, as it is this action that helps the brain reduce anxiety and promotes both physical and mental relaxation.

There Are Four Main Reasons People Start Using and Eventually Start to Abuse the Use Of Phenibut Supplement:

  • As a brain stimulant. It is popular among college students, artists, athletes, and other high cognitive professionals as a nootropic or a “smart drug.” The use of this gabapentin analog for this purpose eventually creates a dependency in the user's brain and a consequent Phenibut addiction.
  • For mental health disorders. Anxiety treatment is another widespread use of this drug since it supposedly has properties that can penetrate the blood-brain barrier and directly affect the brain to quickly reduce anxiety, depression, insomnia, and alcohol withdrawal symptoms. Many people who suffer from these disorders are attracted to distributors' sale offers due to the quick and robust drug effects.
  • As a recreational drug. More recently, Fenibut HCL powder, in particular, is being used as a recreational drug by people. One of the most desired features of this substance is the dopamine increase that it delivers.
  • For muscle-building purposes. While not clinically proven, there is a general belief that the GABA receptors in the brain stay active even after the substance has been cleared from the bloodstream, which is connected to increasing human growth hormone levels. Abusing or excessively redosing Phenibut capsules for this purpose bring dangerously high health risks for the body, delivering the exact opposite of the intention of taking this substance.

It is important to note that the medical community in Western countries is not fully endorsing this substance due to the lack of clinical evidence.

Different supplements including phenibut in wooden spoons.

Still, some people tend to abuse the drug, considering it a healthy and natural supplement with no side effects.

Phenibut Side Effects

Even though users widely consider it as a “wonder drug,” there are plenty of side effects that come with using it. Due to the lack of clinical research of Fenibut as a prescription drug in the US, there are no definite conclusions about the cause of Phenibut side effects. However, reportedly the most common reason for the adverse reactions is taking over high doses of this drug.

Short-Term Side Effects

Taking low doses does not save the user from having adverse Phenibut side effects, although the severity of these reactions differs according to the dose. It is important to note that most of these are anecdotal evidence by users and have not been extensively studied or researched.

Following Are Some Common Phenibut Side Effects:

  • Nausea
  • Blurred vision
  • Stomach cramps
  • Persistent fatigue
  • Troubles in breathing
  • Muscle spasms
  • Anxiety
  • Sleepiness
  • Headache
  • Allergic reactions
  • Anxiety and depression
  • Diarrhea

As stated above, the severity of symptoms can depend on the dosage taken. Higher doses can cause more Phenibut side effects. Following are some of the expected severe side effects caused by the Fenibut abuse by taking overly high doses.

They Include:

  • Unconsciousness (blackouts)
  • Seizures
  • Severe hangover symptoms
  • Motor impairment
  • Trouble breathing

Side Effects Caused By Long-Term Use

The most extreme long-term effects of Fenibut occur when the substance starts directly affecting the liver and the bloodstream. Perhaps the most extreme consequence of long-term use of this substance is psychosis, which occurs due to dissociative intoxication and prolonged withdrawal. This is a rare but possible occurrence with inotropic agents such as Fenibut.

Following Are Some Of the Long-Term Effects:

  • Depression
  • Agitation
  • Persistent muscle spasms
  • Heart rate escalation
  • Severe fatigue
  • Fatty liver disease
  • Eosinophilia
  • Psychosis

According to the Centers for Disease Control and Prevention, between 2009 and 2019 poison centers reported 80 cases when Phenibut use led to coma, including one adolescent. Besides, there was one death reported caused solely by fenibut (no other drugs involved).

Phenibut Interactions

Like any other drugs, fenibut can have mild or severe interactions with other medications. It can potentiate or extend the duration of other central nervous system depressants, like sedatives, opioids, or alcohol.

Phenibut And Alcohol

Both Phenibut and alcohol affect the way GABA receptors function. Given the similarities in their actions, users often combine them for added benefit. This combination may produce a “buzz” feeling after having fewer alcoholic drinks for some people. However, this is considered a dangerous practice with a very high risk of unwanted side effects.

Woman taking phenibut with alcohol.

At the recommended dosage, the mild stimulation of GABA receptors gives the desired and well-tolerated feelings of relaxation and enhanced sociability. But, overstimulation of GABA receptors can result in severe consequences for one’s health and safety.

Phenibut and alcohol interaction may cause extreme drowsiness, sedation, nausea, and vomiting. Toxicity and overdose may also occur. Severe overstimulation cases often lead to CNS depression, loss of consciousness, choking, and short-term memory loss.

Phenibut And Kratom

Users mix Fhenibut and Kratom for pain relief or opiate withdrawal syndrome. Both drugs act on the GABA receptors in the brain. Fenibut produces tranquilizing effects, which reduce anxiety and fear and improves sleep patterns. It also potentiates the actions of Kratom, thus the effects last longer. There is an increased pain threshold effect, and it becomes more sedating.

At low and medium doses, one will experience soothing and calming effects. However, as the dose increases, one may suffer from extreme sedation or a coma-like sleep. Nausea and vomiting are also very common. Some users reported on forums that with continuous use of this drug combination, constipation and blurred vision are likely to occur. Some even claimed episodes of rebound insomnia.

Adderall And Phenibut

Adderall And Phenibut are popularly used under the presumption that their combined actions can help reduce anxiety. Fenibut has a sedative effect, which helps avoid the irritability that comes after taking Adderall. This combination has much greater effectiveness in reducing the chance of Adderall stimulation producing anxiety. While this is helpful for young adults struggling with a social anxiety disorder, this combination may also cause severe health issues.

Taking both types of drugs all at once is also hard on the heart. Stimulants speed up the heart rate, while depressants work to slow it. Severe interaction gives mixed messages to the heart and may lead to dysrhythmias.

Phenibut And Caffeine

No adverse interactions between Anfiven and caffeine have been reported. In most reviews posted on forums, these two substances can work together well at the right dosage. Users drink coffee a few minutes after taking Phenibut. The adverse effects of both drugs negate one another, hence being used by many as combination drugs.

Phenibut And DXM

People use Phenibut and DXM together for recreational purposes. While DXM is most often used for cough, it is also a morphinan class of drugs with sedative and dissociative properties.

There were reported cases of high blood pressure from this combination, as posted on forums.

Phenibut Addiction

The reason for the rigorousness of Fenibut long-term effects is the formation of physical dependence that occurs in the human brain for this substance. As a result of broad structural similarities of this substance to the brain’s natural neurotransmitters, the body is unable to distinguish one from another, forming a dependence on the stimulation of the GABA receptors by this extra addition.

Addicted girl looking at phenibut capsules.

This dependence eventually evolves into a Phenibut addiction since the drug also stimulates the dopamine receptors of the brain that causes a feeling of intense exhilaration. Depending on users’ tolerance level, it can take only one session of using it to develop an absolute dependence.

Another reason for the fast-developing physical Phenibut addiction is the high tolerance on the substance, especially for young people between the ages of 19 and 24. It leads them to increase the amount of substance intake to get the desired effect that can ultimately lead to high and dangerous health risks.

Signs And Symptoms Of Phenibut Addiction

Following are some signs and symptoms that can occur when a user approaches an addictive state with continued use of Phenibut supplement. They often increase mental health disorders that users try to reduce, leading them to experience social anxiety and depression.

Physical signs:

  • Paranoia
  • Muscle tension
  • Fatigue
  • Headache
  • Nausea
  • Hallucinations
  • Hyper-activeness
  • Tremors

Psychological And Behavioral signs

  • Anxiety
  • Depression
  • Dysphoria
  • Cravings
  • Stress
  • Aggressiveness
  • Being agitated
  • Difficulty in maintaining friendship and relationships
  • Criminal behavior

Phenibut Half-Life

On average, Phenibut half-life is 5.3 hours. This means that it takes this long for a dose to be broken down by half. In cases of an overdose, it may take longer. Despite this relatively short Phenibut half-life, its effects last between 15 to 24 hours (about 3 to 5 half-lives) since its actions on the GABA receptors linger long after the kidneys have excreted it.

Does Phenibut Show Up On Drug Tests?

The answer to this depends on which medium is used for the analysis. There are four standard media used for drug screening – blood, urine, saliva, and hair. The detection times will correspond with Phenibut half-life.

Blood Tests

The substance can be detected in blood drug tests within 79.5 hours after the last dose. This is the time it takes for the drug to be eliminated from the blood. However, frequent use of the drug could widen the detection window using blood analysis.

Lab worker checking the blood sample.

Fenibut cannot be detected using the standard immunoassay toxic screening techniques but with advanced tests such as gas chromatography- or liquid chromatography-mass spectrometry (GC/MS and LC/MS, respectively).

Urine Tests

Screening for this substance using urine is likely to yield a positive result within 4 days to up to 4 weeks after its use. Since much of the substance is excreted unchanged by the kidneys, it can easily be detected. However, its metabolites are inactive and not recognized by standard urine assays.

Saliva Tests

Screening with saliva may yield a positive result for Phenibut supplement. However, this test can only detect it within 12-24 hours of its last use. It is particularly useful for detecting very recent use of the substance.

Hair Tests

Hair tests may yield positive results up to 3 months after the last dose, depending on the length of the hair obtained. Since the concentration of Fenibut in hair is typically shallow, only highly-sensitive hair detection techniques can detect it. Besides, hair tests may not detect the substance within seven days of its use.

Help Is Available

Fenibut abuse can be dangerous for a patient and lead to many potential side effects, including a risk of intoxication when exceptionally high doses of this supplement are taken. Taking it with alcohol or other CNS depressants can cause a dangerous interaction, requiring additional treatment. Drug abuse is a serious problem, even if it is bought as a supplement. For many patients, stopping the drug’s use can be difficult due to the development of Phenibut addiction and withdrawal symptoms upon cessation.

Fortunately, treatment help is available for patients who are having a hard time quitting Fenibut. Various rehabilitation facilities are equipped with the appropriate medication, facilities, and healthcare professionals experienced in dealing with patients who have developed a dependency or addiction to Fenibut.

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Published on: April 10th, 2019

Updated on: July 5th, 2021

About Author

Roger Weiss, MD

Dr. Roger Weiss is a practicing mental health specialist at the hospital. Dr. Weiss combines his clinical practice and medical writing career since 2009. Apart from these activities, Dr. Weiss also delivers lectures for youth, former addicts, and everyone interested in topics such as substance abuse and treatment.

Medically Reviewed by

Michael Espelin APRN

8 years of nursing experience in wide variety of behavioral and addition settings that include adult inpatient and outpatient mental health services with substance use disorders, and geriatric long-term care and hospice care.  He has a particular interest in psychopharmacology, nutritional psychiatry, and alternative treatment options involving particular vitamins, dietary supplements, and administering auricular acupuncture.