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
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
The published record
Papers and trials about Phenibut
114 papers tagged human · 98 not reviews or lab · 14 clinical trial publications
Furthest stage reached: Approved outside the US, Russia
Counted from Europe PMC indexing, not read by a person; a human tag can land on reviews, commentary or lab papers; clinical trial publications is the narrower count.
At a glance
Four things to know about Phenibut
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 solution No 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.
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.Not in the United States. Phenibut has no FDA approval and is sold there labeled for laboratory research only, so there is no legal route to buy it for human use. It is approved in Russia.
- Approval statusResearch only
- RouteBy mouth (oral)
- Checked22 September 2026
- Approved outside the USRussia: Registered in Russia as a prescription medicine, with several 250 mg tablet products from different manufacturers. Not approved in the US.This does not change the United States position above.
- DoseFrom community reports. No regulator or trial established this dose.
- Vial sizeFrom what vendors typically list; not a recommendation.
- Sources
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.
What else is like Phenibut?
Others in Brain, mood and sleep, side by side.If you're weighing Phenibut, it's worth reading Trofinetide (Daybue), Ziconotide, 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
An approved oral treatment for Rett syndrome, built from the first three amino acids of IGF-1 with one methyl group added.
- Dose
- 5,000 to 12,000 mg twice daily by weight (label)
- How often
- Twice daily
The FDA-approved cone-snail peptide for severe chronic pain, delivered only into the spinal fluid.
- Dose
- 2.4 up to 19.2 mcg per day by continuous pump (label)
- How often
- Continuous infusion
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
Guides for this compound
- 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 hospitalization, including psychotic symptoms.
Beyond these, 304 records are indexed. Browse the records