Phenibut_Dosage, benefits & legal status
Also known as fenibut, beta-phenyl-GABA, phenyl-GABA, 4-amino-3-phenylbutanoic acid, Anvifen, Noofen
A Russian anxiety drug sold as a nootropic. Stopping it suddenly can be dangerous.
Common vial size is what vendors typically sell, not a recommendation. Enter your own vial in the calculator.
What is Phenibut?
Plain language first. The technical label stays, but it never stands alone.Overview
It is a sedative that works on the same receptor as baclofen, and tolerance builds quickly.
Phenibut is beta-phenyl-GABA, a GABA-B receptor agonist developed in the Soviet Union and still prescribed in Russia and Latvia for anxiety, insomnia and alcohol withdrawal.
What it's used for
A prescription anxiety drug in some countries, sold in the US as a calm-and-focus supplement, with a real dependence problem.
How does Phenibut work?
What it does in the body, and where.Phenibut is GABA with a phenyl ring attached, and that ring is what lets it reach the brain.
- 01GABA itself barely crosses into the brainThat is why GABA sold as a supplement does very little. Adding the phenyl ring solves that problem.
- 02It activates GABA-B receptorsThe same receptor baclofen works on, though phenibut is far weaker at it. The effect is sedation and reduced anxiety.
- 03The receptor adaptsRegular use turns the receptor response down, so the dose stops working and people raise it. This is the mechanism of tolerance, and it is fast.
- 04Withdrawal is the adapted state without the drugOnce the brain has compensated, removing the drug leaves that compensation exposed. The result looks like benzodiazepine or alcohol withdrawal, and can include seizures.
A schematic of the compound's mechanism, not a diagnostic image.
What else is it used for?
Each use below carries its own evidence level. Approved means regulators have cleared it for that purpose. Investigational means it is in trials. Early research means it is being studied and is not established.
- Anxiety, insomnia and alcohol withdrawal, where it is a prescription medicine in Russia and LatviaClinical use
- Sleep and stress reduction, as sold in the USResearch only
- Focus and cognitive enhancement, as soldResearch only
How much, and do you cycle it?
The range, and whether you take breaks.No safe self-directed dose is established, not daily, if at all. Regular use is the problem, not the solutionNo range
There is no cycling schedule that makes this safe to take regularly. Tolerance builds fast enough that a routine of any kind tends to escalate. Where it is prescribed, courses are short and supervised.
How long does it stay in the body?
The half-life, and where the figure comes from.About 5 hoursHuman study
Commonly reported at around five hours. That figure understates how long the effect lasts, and it says nothing about the timeline of tolerance and withdrawal, which is measured in weeks rather than hours.
Not yet traced to a primary source.
You can compare this against the whole library to see where it sits.
What does it cost?
Typical dose and cost, in plain numbers.Phenibut is not injected
It is taken by mouth (oral). We do not publish a dose range for this one, and that is deliberate. The doses used where it is a prescription medicine are set and monitored by a prescriber, and the pattern that produces dependence is regular self-directed use at escalating doses. Publishing a number here would be an instruction to start.
How do you store it?
Before mixing, and after.Room temperature. Cool, dry, out of light.
Phenibut is taken as a pill or capsule. Keep it in its original container at room temperature, away from heat, humidity, and direct sun. No fridge or mixing needed. Check the expiration date on the bottle.
What are the side effects and cautions?
Known cautions and warnings for this compound.Who should avoid it
- Drinking alcohol, or taking benzodiazepines, opioids or any other sedative, since the effects stack
- A history of substance dependence of any kind
- Driving or operating machinery
- Pregnancy and breastfeeding
- Stopping suddenly after regular use, which is itself the dangerous part
Stop and get help
- Do not stop suddenly if you have been taking it regularly. Abrupt withdrawal can cause seizures, and tapering needs medical supervision
- Seek urgent care for hallucinations, severe agitation, confusion, or a seizure
- Seek urgent care for a very slow heart rate, slowed breathing, or unresponsiveness, especially if alcohol or another sedative is involved
- Talk to a doctor before changing your dose in either direction if you have been using it for more than a few weeks
Common effects
- Sedation and drowsiness
- Confusion and slurred speech at higher doses
- Dizziness and balance problems
- Nausea and vomiting
- Irritability and low mood the following day
- Rapidly rising tolerance, so the same dose stops working
Where this page says nothing is established, that means nobody has studied it, not that a compound is safe.
Is Phenibut approved?
And where the numbers on this page come from.No. Phenibut is not approved for any use, anywhere. It is sold labelled for laboratory research only, and there is no legal route to buy it for human use. It is approved in Russia and Latvia, but not in the United States.
- Approval statusResearch only
- RouteBy mouth (oral)
- CheckedAugust 2026
- Approved outside the USRussia, Latvia: Prescribed in Russia and Latvia for anxiety, insomnia and alcohol withdrawal, under names including Anvifen and Noofen.This does not change the United States position above.
What has happened recently
Never approved by the FDA for anything, and it cannot lawfully be sold as a supplement either. The FDA has stated that phenibut does not meet the statutory definition of a dietary ingredient, which makes any product declaring it as one misbranded. It issued warning letters to three companies in April 2019, and in June 2023 a federal court entered an order of permanent injunction in a phenibut case in the District of Massachusetts. It is not a federally controlled substance, so buying and possessing it is not illegal, and it is on the US Department of Defense prohibited ingredients list for service members.
You can compare this against the whole library, or read how to check a seller.
- DoseFrom research and community reports. No regulator has reviewed this dose.
- Vial sizeFrom what vendors typically list; not a recommendation.
- Sources
- Reviewed24 August 2026
What else is like Phenibut?
Others in Brain, mood and sleep, side by side.If you're weighing Phenibut, it's worth reading GB-115, Semax, and Selank in the same class.
A Russian anxiety drug sold as a nootropic. Stopping it suddenly can be dangerous.
- Dose
- No safe self-directed dose is established
- How often
- Not daily, if at all
A Russian anti-anxiety dipeptide that blocks a panic receptor instead of sedating you.
- Dose
- 1 mg per day in the published human study
- How often
- Daily in the study
A peptide used for sharper focus, memory, and mental clarity.
- Dose
- 0.2 up to 0.6 mg per day
- How often
- 1-2x daily
A peptide that eases anxiety while keeping you clear-headed.
- Dose
- 0.25 up to 0.5 mg per day
- How often
- 1-2x daily
10What these words mean
Show glossary +
What these words mean
- 503A and 503B
- The two kinds of compounding pharmacy in US law. A 503A pharmacy prepares medicine for one named patient. A 503B outsourcing facility makes larger batches under stricter manufacturing rules.
- Agonist
- Something that switches a receptor on. The opposite is an antagonist. It blocks the receptor instead.
- Amino acid
- The building blocks that link together in a chain to make a peptide or a protein. The order they sit in is what makes one peptide different from another.
- Amylin
- A hormone released alongside insulin that slows the stomach emptying and reduces appetite. Several weight loss compounds copy it.
- Analog
- A compound built to copy a natural one with small deliberate changes, usually so it lasts longer or holds onto its target more tightly.
- Animal study
- Research done in rats, mice or other animals. Most findings do not repeat in people, so an animal result is a reason to keep looking. It is not a reason to act.
- Antibody
- A large immune protein, far bigger than a peptide, engineered to lock onto one specific target. These are made by drug companies and are not sold as research powders.
- Bacteriostatic water
- Sterile water with a tiny amount of preservative, used to mix powdered peptides.
- Banned in drug-tested sport
- Prohibited by the World Anti-Doping Agency (WADA); using it can disqualify a competing athlete.
- Bioavailability
- How much of a dose actually reaches your bloodstream. Most peptides survive stomach acid badly, so most of them are injected instead of swallowed.
- Bioregulator
- Very short peptides from a Russian research tradition, usually two to four amino acids long, sold for supporting a specific organ. Human evidence is thin and most of it is published in Russian.
- Blend
- One vial holding more than one compound, mixed together by the seller. Working out a dose means working out each ingredient separately, because they are rarely present in equal amounts.
- Boxed warning
- The most serious warning the FDA puts on a drug label, printed inside a black border. It flags a risk considered severe enough to sit above everything else on the label.
- Bulks list
- The FDA's list of ingredients that compounding pharmacies are allowed to use. A substance can sit under review on it for years without anything being decided either way.
- Certificate of analysis (COA)
- A lab report on a batch of product. It only means something if it names the batch you actually received, comes from an independent lab, and can be checked with that lab.
- Clinical trial
- A study that gives a treatment to people under a written plan and measures what happens. It is the only kind of evidence that can show something works in humans.
- Compounding
- A licensed pharmacy preparing a medicine to order. Being allowed to compound something is not the same as the FDA approving it, and the two get mixed up constantly.
- Concentration
- How strong the mixed peptide is, in milligrams per milliliter (mg/mL). More water makes it weaker; less water makes it stronger.
- Cycle
- A stretch of time using a compound followed by a break. Most cycling patterns come from community practice. Very few have been tested.
- DAC
- Short for Drug Affinity Complex. An attachment added to a peptide so it grabs onto a blood protein and stays in the body for days instead of minutes.
- Dead space
- The small amount of liquid left sitting inside the needle and hub after you inject. On very small doses it can be a real share of what you meant to take.
- Dilute
- Adding more liquid to make a mix weaker. The amount of peptide in the vial does not change. It is just spread through more water, so each draw is bigger.
- Endpoint
- The result a trial said in advance that it would measure. A study can be reported as positive and still have missed the endpoint it set out to hit.
- FDA approved
- Reviewed by the FDA and cleared for a specific use, in a specific form, at a specific dose. Approval for one use is not approval for another, and approval in another country is not approval here.
- Fragment
- A short piece cut out of a larger natural protein. A fragment can behave very differently from the whole protein it came from, so evidence about one does not transfer to the other.
- Ghrelin
- The hunger hormone. Some growth hormone compounds work by copying it, so they can make you noticeably hungrier.
- GHRH
- A natural signal telling the pituitary gland to release growth hormone. Several compounds copy it.
- GHRP
- A second, separate signal that also triggers growth hormone release, through a different door than GHRH. This is why the two types are often used together.
- GLP-1
- A natural gut hormone that lowers appetite and blood sugar. Drugs that copy it, like semaglutide, are used for weight loss.
- Growth hormone secretagogue
- A compound that nudges your body to release more of its own growth hormone, rather than injecting the hormone itself.
- Half-life
- How long a compound stays active in your body. A longer half-life means you inject less often.
- HPLC
- A lab method that separates out everything in a sample so the amounts can be measured. It shows how much of the main ingredient is there. It does not confirm that the main ingredient is the right molecule.
- In vitro
- Done in a dish or a test tube, on cells outside a living body. It is the earliest kind of evidence there is.
- Injection site
- The spot on the body where you inject. Moving it around gives the skin and fat underneath time to recover between doses.
- Intramuscular (IM)
- An injection into a muscle, using a longer needle.
- Intravenous (IV)
- An injection into a vein. It needs training and equipment and is not something to do at home.
- Investigational
- Still being tested in clinical trials and not yet approved or legally sold for general use.
- Lyophilized
- Freeze-dried into a powder so it keeps longer. That is the white cake or dust in the bottom of an unmixed vial.
- Mass spectrometry
- A lab method that weighs molecules to confirm what they are. HPLC answers how much is in the sample. This answers what it is.
- mcg and mg
- Units of dose. 1 milligram (mg) equals 1,000 micrograms (mcg).
- Myostatin
- A natural brake on muscle growth. Several compounds are built to block it, though human results have been far smaller than the animal work suggested.
- Off-label
- A doctor prescribing an approved drug for something other than its approved use. This is legal and common, and it is different from a compound having no approval at all.
- Orphan drug designation
- A status given to treatments for rare conditions to make them worth developing. It is an incentive, not an approval, and a compound can hold it while being approved for nothing.
- PCAC
- The FDA advisory committee that reviews compounding ingredients. It recommends. It does not approve, and the FDA does not have to follow what it says.
- Peer review
- Other scientists checking a paper before a journal publishes it. It filters out some bad work. It does not make a finding true.
- Peptide vs small molecule
- A peptide is a short chain of amino acids. A few items here (like MK-677 or methylene blue) are small molecules, not true peptides, but people use them the same way.
- Placebo
- A dummy treatment given for comparison. Without one it is very hard to tell a real effect apart from expectation and time passing.
- Purity
- The share of a sample that is the intended compound, usually given as a percentage. A high purity number on the wrong molecule is still the wrong molecule.
- Randomized
- Deciding by chance who gets which treatment, so the two groups are comparable. Studies that skip this are much easier to read the wrong way.
- Receptor
- A docking point on a cell that a compound attaches to. If a cell has no matching receptor, the compound does nothing to it.
- Reconstitution
- Mixing a powdered peptide with liquid (bacteriostatic water) so it can be drawn into a syringe.
- Research only
- No approved dose or use in people. Sold for research and not reviewed by the FDA for safety or quality.
- Stack
- Using more than one compound at the same time. Almost no combinations have been tested together in people, so a stack is usually built on guesswork.
- Sterile water
- Water with nothing added to stop bacteria growing. It works for a single dose, but a vial mixed with it should not be kept and used again.
- Subcutaneous
- An injection just under the skin, into the fat layer, usually with a short, thin insulin needle.
- Titrate
- Starting at a low dose and increasing it slowly over time so your body adjusts and side effects stay mild.
- Trial phases
- The stages of human testing. Phase 1 checks safety in a small group, phase 2 looks for an effect, and phase 3 tests it against a comparison in a large group.
- Units (on the syringe)
- The marks on an insulin syringe. 100 units equals 1 mL. They measure how much liquid you draw, not the dose in milligrams.
Guides for this compound
- How to Reconstitute a Peptide
Mix peptide powder with bacteriostatic water, step by step.
- mcg vs mg: The Peptide Dosing Mistake to Avoid
Your vial says mg and your protocol says mcg. Here is the conversion and how to check it.
- How to Read a Peptide COA
What the purity number does and does not tell you, and how to spot an edited report.
- How to Vet a Peptide Vendor
Independent COAs, HPLC purity, and the red flags that mean walk away.
Sources
- FDA, phenibut in dietary supplements(2023)Phenibut does not meet the statutory definition of a dietary ingredient; warning letters issued and a permanent injunction entered in June 2023.
- US Department of Defense, Operation Supplement Safety on phenibut(2025)Prohibited for service members; documented dependence, tolerance and withdrawal including hallucinations and arrhythmia.
- Ahuja et al., phenibut dependence and withdrawal management, Case Reports in Psychiatry(2018)Withdrawal can be severe and require hospitalisation, including psychotic symptoms.
Last reviewed 24 August 2026
Peptide Decoding is published by Decoded Sciences LLC. We take no payment from vendors for coverage, inclusion or ranking, and our affiliate relationships are disclosed in full.