Also known as

Pheno, phenobarbitone, luminal




A barbituric acid derivative that acts as a nonselective central nervous system depressant. It promotes binding to inhibitory gamma-aminobutyric acid subtype receptors, and modulates chloride currents through receptor channels. It also inhibits glutamate induced depolarizations [1].

Medical usage

For the treatment of all types of seizures except absence seizures [1].

Why take it?

Sought after effects

  • euphoric feelings,
  • reduced inhibition,
  • feelings of calm/relaxation,
  • increased ability to sleep [2].




  • threshold 25 - 50 mg,
  • light 50 - 100 mg,
  • common 100 - 150 mg,
  • strong 150 - 300 mg,
  • heavy 300 mg + [3].

How long do its effects last?

Onset of effects

  • oral - 15 - 60 minutes [3], 15 - 45 minutes [4].
  • intravenous - 1 - 5 minutes [4].


  • oral - 4 - 6 hours [3].

Duration of effects

  • oral - 5 - 8 hours [4].
  • intravenous - 4 - 6 hours [4].


  • oral - 1 - 48 hours [3], 1 - 24 hours [4].
  • intravenous - 1 - 24 hours [4].


Barbiturates behave similarly to benzodiazepines. Phenobarbital binds to an allosteric site on the GABAA receptor and potentiates the effects of the endogenous ligand, gamma-aminobutyric acid. When barbiturates bind to the GABAA receptor, it causes the ion pore to open for extended periods of time, causing an increase of intracellular chlorine ion concentrations. As this site is the most prolific inhibitory receptor set within the brain, its modulation results in the sedating (or calming effects) of barbiturates on the nervous system.

Phenobarbital has a bioavailability of around 95%. 20% - 45% of phenobarbital will bind to proteins. Phenobarbital's biological half life is 53 - 118 hours. It is metabolised by the liver and excreted by the kidneys and intestines [3].


Phenobarbital, the longest-acting barbiturate, is used for its anticonvulsant and sedative-hypnotic properties in the management of all seizure disorders except absence (petit mal) [1].


Absorbed in varying degrees following oral, rectal or parenteral administration. The salts are more rapidly absorbed than are the acids. The rate of absorption is increased if the sodium salt is ingested as a dilute solution or taken on an empty stomach [1].


70% - 90% [5].


Hepatic (mostly via CYP2C19) [1].


53 to 118 hours (mean 79 hours) [1].


Excretion - urine (major) [5].

Lethal dosage

LD50 3.1244 mol/kg in rats [1].


Tolerance will develop to the sedative-hypnotic effects of phenobarbital after prolonged use. It is unknown exactly how long it takes for tolerance to reach baseline. Phenobarbital presents cross-tolerance with all barbiturates, meaning that after its consumption all barbiturates will have a reduced effect [3].

Mechanism of action

Phenobarbital acts on GABAA receptors, increasing synaptic inhibition. This has the effect of elevating seizure threshold and reducing the spread of seizure activity from a seizure focus. Phenobarbital may also inhibit calcium channels, resulting in a decrease in excitatory transmitter release. The sedative-hypnotic effects of phenobarbital are likely the result of its effect on the polysynaptic midbrain reticular formation, which controls CNS arousal [1].


Barbiturate overdose may occur when a barbiturate is taken in extremely heavy quantities or concurrently with other depressants. This is particularly dangerous with other GABAergic depressants such as benzodiazepines and alcohol since they work in a similar fashion, but bind to distinct allosteric sites on the GABAA receptor, thus their effects potentiate one another. Benzodiazepines increase the frequency in which the chlorine ion pore opens on the GABAA receptor while barbiturates increase the duration in which they are open, meaning when both are consumed, the ion pore will open more frequently and stay open longer [6]. Barbiturate overdose is a medical emergency that may lead to a coma, permanent brain injury or death if not treated promptly and properly. Barbiturate overdose has an increased frequency of serious adverse effects when compared to other depressants [3].

Signs of usage

  • onset of withdrawal symptoms after not using the drug for a period of time,
  • continuing to consume the drug after the medical need for the drug has passed,
  • consuming the prescription at a faster rate than recommended,
  • frequently requesting refills from the doctor,
  • visiting multiple doctors to obtain a prescription for the same medical problem,
  • stealing medication from others,
  • stealing or forging prescriptions,
  • increased tolerance to the drug's affects,
  • uncontrolled consumption of phenobarbital,
  • irresponsible or dangerous behaviour while under the influence of the drug,
  • abandonment of previously enjoyable activities,
  • obsessive thoughts about the next dose of the drug,
  • continuing to use the drug despite its negative effects [7],
  • unexplained weight loss,
  • irritability,
  • anxiety,
  • fatigue,
  • sleep issues,
  • odd behaviour [8].


Short-term effects

  • drowsiness,
  • fatigue,
  • nausea,
  • vomiting,
  • slowed heart rate,
  • respiratory depression,
  • uncoordinated muscle movements,
  • nystagmus,
  • dizziness,
  • impaired thinking processes,
  • paradoxical neural excitation,
  • coma,
  • overdose [9].

Long-term effects

  • difficulty maintaining alertness,
  • poor functioning at home, work, or school,
  • mood disturbances,
  • irritability,
  • depression,
  • suicidality,
  • cognitive decline,
  • problems with memory consolidation and recall [9].

Physical effects

  • muscle relaxation,
  • physical euphoria,
  • motor control loss,
  • respiratory depression,
  • sedation,
  • seizure suppression,
  • decreased blood pressure,
  • dizziness [3].

Cognitive effects

  • cognitive euphoria,
  • compulsive redosing,
  • delusions,
  • amnesia,
  • analysis suppression,
  • anxiety suppression,
  • decreased libido,
  • disinhibition,
  • emotion suppression,
  • information processing suppression,
  • language suppression,
  • thought deceleration [3].

Visual effects

  • acuity suppression [3].


Less common

  • mental dullness,
  • constipation,
  • diarrhoea,
  • nausea,
  • vomiting,
  • megaloblastic (folate-deficiency) anaemia [5].




  • blisters and lesions on the skin,
  • dilated pupils,
  • double vision,
  • ataxia,
  • loss of muscular coordination,
  • altered consciousness and behaviour,
  • slurred speech,
  • liver damage [10].


  • nystagmus,
  • loss of coordination,
  • drowsiness,
  • slowed breathing,
  • drop in body temperature,
  • blisters [11],
  • confusion,
  • delirium,
  • deep sleep,
  • coma,
  • low blood pressure,
  • slurred speech,
  • unsteady gait,
  • weak pulse,
  • excitement,
  • headaches [12].

Dangerous interactions

Although many drugs are safe on their own, they can become dangerous and even life-threatening when combined with other substances. The list below contains some common potentially dangerous combinations, but may not include all of them. Certain combinations may be harmless in low doses of each but still increase the potential risk of death. Independent research should always be done to ensure that a combination of two or more substances is safe before consumption [3].

  • Depressants (1,4-Butanediol, 2-methyl-2-butanol, alcohol, barbiturates, GBL / GHB, methaqualone, opioids) - This combination can result in dangerous or even fatal levels of respiratory depression. These substances potentiate the muscle relaxation, sedation and amnesia caused by one another and can lead to unexpected loss of consciousness at high doses. There is also an increased risk of vomiting during unconsciousness and death from the resulting suffocation. If this occurs, users should try to fall asleep in the recovery position or have a friend move them into it.
  • Dissociatives - This combination can lead to an increased risk of vomiting during unconsciousness and death from the resulting suffocation. If this occurs, users should attempt to fall asleep in the recovery position or have a friend move them into it.
  • Stimulants - It is unsafe to combine barbiturates with stimulants due to the risk of excessive intoxication. Stimulants decrease the sedative effect of barbiturates, which is the main factor most people consider when determining their level of intoxication. Once the stimulant wears off, the effects of barbiturates will be considerably increased, leading to intensified disinhibition as well as other effects. If combined, one should strictly limit themselves to only dosing a certain amount of barbiturates per hour. This combination can also potentially result in severe dehydration if hydration is not monitored [3].


  • anxiety,
  • muscle twitching,
  • tremors,
  • weakness,
  • dizziness,
  • changes in vision,
  • nausea,
  • vomiting,
  • seizures,
  • confusion,
  • insomnia,
  • dizziness or fainting when getting up from a lying position [11],
  • fever,
  • delusions,
  • diarrhoea,
  • loss of appetite,
  • hallucinations,
  • tachycardia,
  • hypertension [2].

Addiction treatment options

There is currently no pharmaceutical drug that can be used to inhibit the affects of phenobarbital. Additionally, abruptly stopping your use of the drug can lead to severe and possibly fatal withdrawal symptoms. The best approach to phenobarbital addiction treatment is to step down the dosage amount until you are no longer consuming the drug. It may take longer to get through the detoxification process, but the withdrawal symptoms may not be as severe.

Phenobarbital addiction is best treated in a phenobarbital rehab center where trained professionals can monitor your progress and help you remain safe while your body is detoxifying itself from the drugs. Additionally, the addiction specialist can provide treatment for co-occurring medical problems that may develop. For example, it is common for a person to feel depressed after stopping his or her use of an addictive substance. Medication and other beneficial therapies can be prescribed to alleviate depression [7].


Detoxification is the first step in phenobarbital addiction treatment. A person cannot obtain sobriety without going through this critical process. Drug residue in the body can spark cravings for the drug, which can lead to drug-seeking behaviors and relapse. To avoid this, it is important to complete the detoxification process even though it may be uncomfortable.

During phenobarbital detox, the body divests itself of all traces of the drug. The process can take a few days to a few weeks depending on the length of time and the dosage amount of phenobarbital the person consumed. Once detoxification has completed, the person usually will not experience physical cravings for the drugs any longer.

Many treatment centers, and especially luxury facilities, prescribe additional therapies that complement the detoxification process. Nutritional therapy is a popular one prescribed to patients. People who abuse drugs often suffer from nutritional deficiencies that can make it harder for the body to heal itself. A person is usually put on a special diet that alleviates this problem and provides the body with the vitamins and minerals it needs to become healthier.

Other popular therapies include the use of herbal remedies, acupuncture, and cognitive-behavioural techniques. It is important to communicate with the person who is helping you through detoxification to make sure your phenobarbital addiction treatment addresses your specific needs [7].

Addiction treatment

After phenobarbital detox is over, the person continues to the next phase of his or her phenobarbital addiction treatment. Typically, this is the phase where the person's psychological addiction to the drug is addressed. Although a person may no longer have physical cravings for the drug, unaddressed mental and emotional cravings can lead to a relapse into the addiction.

Psychological cravings for a drug can sometimes be stronger than physical cravings. A person is typically prescribed counseling or psychotherapy to tackle the underlying reasons for his or her addiction. Additionally, the person is provided with the skills he or she needs for successful reintegration into society and to handle challenges of living a drug-free life [7].

Some of the skills a person may be taught include -

  • recognising situations that may trigger drug cravings or a relapse,
  • learning to handle pressure from peers to take drugs,
  • asking for help when the temptation to take drugs arises,
  • coping skills for handling the stresses of daily life,
  • maintaining mental and physical health [7].

Phenobarbital addiction treatment may include the development of an aftercare plan. Part of this aftercare plan may be to create a support network that will help you maintain your sobriety. You may be encouraged to join a 12-step program that can provide continuing education and socialisation opportunities.

After going through the process of overcoming a phenobarbital addiction, no one wants to relapse into the addiction. However, it is important to be realistic about the possibility of a relapse occurring. It is better to have a plan and never need it than to not have a plan and not know what to do if you relapse. Before leaving the phenobarbital addiction treatment centre, work closely with the addiction specialist on a relapse strategy that will quickly get you back on track if one occurs [7].


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