Overview

Phenibut is a psychoactive chemical that is not legal in the U.S. But products that contain phenibut may still be available for purchase online. People take phenibut for many reasons, but its benefits are not well defined. Common side effects include confusion, drowsiness, fast heartbeat, high blood pressure, irritability, and muscle spasms. Serious side effects are less common and include liver damage, dependence, and withdrawal. Before taking phenibut, make sure to tell your health care provider about any health conditions you have or medicines you are taking.

Uses

What is phenibut used for?

Phenibut is used for various purposes, but its benefits are not well defined and it may cause serious side effects. Some reasons that people use phenibut include the following.

• Substance use disorder or alcohol use disorder
• Anxiety
• Depression
• Posttraumatic stress disorder (PTSD)
• Trouble sleeping (insomnia)

Note: Phenibut is not approved by the FDA for any use. The FDA also does not consider phenibut to be a legal dietary ingredient in the U.S. Learn more about the legal status of phenibut here.

How does phenibut work (mechanism of action)?

Phenibut is a psychoactive substance that is available as a prescription medicine in some countries. In the U.S., phenibut is not a legal ingredient and cannot be legally sold in any products. But it may still be available for purchase online.

Phenibut is similar to a natural brain chemical called gamma-aminobutyric acid (GABA). Your brain and nervous system contain GABA receptors. Phenibut can bind to these receptors, causing the signals sent by your brain and nerves to slow down. This has led to interest in taking phenibut for issues such as anxiety and trouble sleeping. But the benefits of phenibut for any use are not well defined, and many people who use phenibut develop a tolerance to its effects. This means that they need to keep increasing their dose to notice any benefits. Some people may also develop physical dependence on phenibut. See the Side Effects section for more information.

How should I store phenibut?

You should store phenibut according to the product label. Most dietary supplements should be kept in a cool, dry location that is out of the reach of children and pets and not in direct sunlight.

Side Effects

What are the most common side effects of phenibut?

The most common side effects of phenibut are listed below. These side effects may vary depending on the dose you are taking or the specific product you are using. Tell your health care provider if you have any of these side effects that bother you.

• Confusion
• Drowsiness or sleepiness
• Fast heartbeat
• High blood pressure
• Irritability
• Muscle spasms

There may be other side effects of phenibut that are not listed here. Contact your health care provider if you think you are having a side effect of a supplement. In the U.S., you can report side effects to the FDA at www.safetyreporting.hhs.gov or by calling 888-SAFEFOOD (888-723-3366). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of phenibut?

While less common, the most serious side effects of phenibut are described below, along with what to do if they happen.

Severe Allergic Reactions. Phenibut may cause allergic reactions, which can be serious. Stop taking phenibut and get help right away if you have any of the following symptoms of a serious allergic reaction.

• Breathing problems or wheezing
• Racing heart
• Fever or general ill feeling
• Swollen lymph nodes
• Swelling of the face, lips, mouth, tongue, or throat
• Trouble swallowing or throat tightness
• Itching or skin rash
• Bumps on the skin called hives that can be red, pink, white, or brown depending on your skin tone
• Nausea or vomiting
• Dizziness, feeling lightheaded, or fainting
• Stomach cramps
• Joint pain

Dependence and Withdrawal Reactions.Phenibut may cause physical dependence, which means your body comes to rely on it. This risk may be higher in people who use phenibut regularly. If you stop phenibut suddenly, it could lead to withdrawal symptoms, which may be life-threatening. If you have been using phenibut regularly for a while, do not stop taking it without speaking with your health care provider first. Your health care provider may be able to help you stop phenibut in a way that will reduce the risk of withdrawal reactions. Call your health care provider right away or go to the nearest emergency room if you have any of the following serious symptoms of withdrawal.

• Severe anxiety
• Unusual movements or responses, including tremors and twitching
• Sudden and severe mental or nervous system changes
• Seeing or hearing things that others do not see or hear, also called hallucinations
• An extreme increase in activity or talking
• Losing touch with reality

Tolerance and Reduced Effect.Some people who take phenibut regularly for a week or longer develop tolerance to its effects. In many cases, people who develop tolerance will need to increase their dose to continue to feel the desired effects. But increasing the dose also increases the risk of serious side effects. If you have been taking phenibut regularly and no longer get the same effects, speak with a health care provider. Your health care provider may be able to help you find a medicine that treats your symptoms without causing tolerance.

Liver Damage.Liver damage, also called hepatotoxicity, might happen when taking phenibut. This risk may be higher in people who use high doses of phenibut for a long time or who also use street drugs or drink alcohol. Stop taking phenibut and call your health care provider right away if you have any of the following symptoms of liver damage.

• Nausea or vomiting
• Stomach or belly pain
• Fever
• Weakness or unusual tiredness
• Itching
• Loss of appetite
• Light-colored poop
• Dark-colored urine (pee)
• Your skin or the whites of your eyes turning yellowish in color (called jaundice)

Precautions

Who should not use phenibut?

Allergies to Ingredients. People who are allergic to any of the following should not take phenibut.

• 4-amino-3-phenylbutanoic acid
• Phenibut
• Any of the ingredients in the specific product

Ask your health care provider if you are not sure what ingredients are in a phenibut product.

What should I know about phenibut before using it?

The FDA does not consider phenibut to be a legal dietary ingredient. However, phenibut products may still be available for purchase online. These products are not regulated and have not been tested to confirm that they contain the ingredients stated on their labels.

Keep phenibut out of the reach of children.

Phenibut can affect your alertness or coordination. Do not drive or do other activities that require alertness or coordination until you know how phenibut affects you.

If you have been taking phenibut on a regular basis, do not stop taking it abruptly without talking to your health care provider. Stopping too quickly may cause serious side effects. See the Side Effects section for more details.

What should I tell my health care provider before using phenibut?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if phenibut is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions.Tell your health care provider if you have any of the following.

• Alcohol use disorder
• Substance use disorder, including cocaine, methamphetamine, or opioid use disorder
• Mental health problems, such as depression or anxiety
• Heart problems
• High blood pressure
• Liver problems
• Seizures
• Upcoming surgery or medical procedure

Other Medicines and Supplements.Phenibut may interact with other medicines and supplements. Before taking phenibut, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. It is not known if or how phenibut could affect pregnancy or harm a fetus. Tell your health care provider if you are pregnant or plan to become pregnant.

Breastfeeding. It is not known if phenibut passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed.

Interactions

Does phenibut interact with foods or drinks?

There are no known interactions between phenibut and foods or drinks.

It is unknown if drinking alcohol will affect phenibut. But the risk of serious side effects may be increased if you drink alcohol while taking phenibut.

Does phenibut interact with medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before taking phenibut.

• Any medicine that causes dizziness and sleepiness, such as prescription pain medicines, sleep medicines, or medicines for anxiety
• A barbiturate, such as butalbital, phenobarbital, or primidone, which is a medicine that may be used to treat insomnia, migraines, or seizures
• A benzodiazepine, such as clonazepam (Klonopin), diazepam (Valium and others), or lorazepam (Ativan and others), which is a medicine used for anxiety, muscle spasms, or seizures
• A muscle relaxant, such as carisoprodol (Soma), cyclobenzaprine, metaxalone, or tizanidine (Zanaflex)
• An opioid, such as codeine, fentanyl, morphine, oxycodone, or tramadol, which is a medicine used to treat certain types of pain
• Street drugs, such as cocaine, heroin, or methamphetamine

The interactions between phenibut and medicines are not fully understood. As with most dietary supplements, the research on drug interactions with phenibut is incomplete. Always check with your health care provider before taking phenibut with any medicines.

Dosing

What should I do if I accidentally use too much phenibut?

If you or someone else has used too much phenibut, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

Phenibut is not considered a legal dietary ingredient in the U.S. and has been associated with serious health problems. It is best to avoid the use of these products entirely.