Substances | 4 min read

Understanding Clonazepam Half-Life

Medically Reviewed

Medically Reviewed By

Dr. Po-Chang Hsu

Dr. Po-Chang Hsu

On May 13, 2024

Written By

Amanda Stevens

Amanda Stevens, B.S.

On May 13, 2024

Clonazepam Half Life

What you will learn

  • Clonazepam is a benzodiazepine used to treat acute seizures and panic disorders.
  • Clonazepam's half-life is 30-40 hours, meaning it will take six to nine days for a single dose to be almost completely eliminated from your system.
  • This long half-life allows for the therapeutic effects of the drug to build, but it also means there is a long period for the drug to leave your system if you are experiencing side effects completely.
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Clonazepam is a benzodiazepine used to treat seizures and panic disorders. The half-life of clonazepam is 30-40 hours. Due to this extended half-life, fewer doses are required per day. Clonazepam’s effects are felt relatively quickly in 20-60 minutes.

Clonazepam does have side effects, and these should be monitored by your healthcare provider. Should you experience side effects and need to stop taking clonazepam, it should be done slowly and monitored closely by your healthcare provider to reduce the likelihood of experiencing withdrawal symptoms.

How Clonazepam Works

Clonazepam is a benzodiazepine that is FDA-approved for the acute, short-term treatment of panic disorder and seizures. [1] It treats numerous types of seizures, including epilepsy and seizures in children, such as petit mal absences, Lennox-Gastaut syndrome, and infantile spasms. It helps treat both panic attacks and seizures by calming down your nervous system. Clonazepam brand names include Klonopin and Ceberclon. Clonazepam is a Schedule IV drug, meaning it has the potential for misuse.[2]

Exactly how clonazepam works is unclear, but it is believed its anticonvulsant and anti-panic effects are due to its ability to bind to the gamma-aminobutyric acid (GABA) neurotransmitter in the central nervous system that blocks impulses between the nerve cells in the brain. Low levels of GABA are linked to mood disorders, anxiety disorders, pain, and seizure disorders.[3]

Clonazepam’s half-life is 30-40 hours.[4] It is metabolized by the liver and excreted by the kidneys through urine. The effects of clonazepam can be felt in 20-60 minutes and reach the peak effects in 1-4 hours.[5] Due to its long half-life, clonazepam accumulates in the body with repeat doses, allowing its therapeutic effects to continue even if a dose of clonazepam is missed. The person reaches the peak accumulation in 5-7 days of regularly taking clonazepam.

A half-life of 30-40 hours means that in that amount of time, 50% of clonazepam will have been eliminated from your body. It takes five elimination half-lives for clonazepam to be out of your system, totaling 6 to 9 days before one dose has been eliminated.

Because of its long half-life, clonazepam must only be taken once or twice daily. However, while this long-acting half-life is positive for its therapeutic effects, it can be considered negative for those who experience side effects, as it will take time for the negative effects of clonazepam to wear off.

Using Clonazepam Half-Life To Determine Dosages and Timing

Understanding the half-life of clonazepam is crucial for individuals and healthcare providers to determine appropriate dosages and treatment times.


Due to its long half-life, clonazepam can be prescribed less frequently, usually once or twice a day. This maintains steady therapeutic levels of the medication in your body and limits the highs and lows experienced with other medications with a shorter half-life.

Depending on a person’s age and health condition, they may metabolize clonazepam more slowly. As a result, dosage must be adjusted and side effects monitored.

Knowing the half-life helps determine the number of daily doses needed to maintain anti-panic effects and to minimize rebound anxiety and withdrawal effects.[6]


Taking clonazepam at a regularly scheduled time helps maintain consistent blood levels in your body, improving the medication’s efficacy and reducing the risk of symptoms and side effects. If you experience a side effect such as drowsiness, you may choose to take your medication at night.

Or if your anxiety is worse early on in the day, you may choose to take clonazepam in the morning. Awareness of symptoms and side effects can help determine the best time to take the medication. Clonazepam is not a prescription drug that should be considered for long-term use.

Other Considerations For Clonazepam

Clonazepam Side Effects

Clonazepam side effects

Knowing the half-life of clonazepam can help indicate when side effects may happen and how long they might last. The most common side effects of clonazepam include [7]

  • drowsiness or sedation
  • dizziness
  • unsteadiness
  • problems with coordination
  • difficulty thinking or remembering
  • increased saliva
  • muscle or joint pain
  • frequent urination
  • blurred vision
  • changes in sex drive or ability

Serious side effects of clonazepam that require immediate emergency medical attention include:[8]

  • respiratory depression
  • rash
  • hives
  • swelling of the eyes, face, lips, tongue, or throat
  • difficulty swallowing
  • hoarseness
  • difficulty breathing

Other medications may interact with clonazepam, resulting in additional adverse effects. Clonazepam has the common side effect of drowsiness. It should be used with caution with other medications that may cause drowsiness, such as antihistamines, narcotic pain medications, opioid cough medications, sleeping aids, and alcohol.[9]

Clonazepam Withdrawal

You can develop physical dependence on clonazepam, especially if taken over an extended period. Clonazepam should not be stopped abruptly as it can worsen the condition you are taking it for and cause withdrawal symptoms. Withdrawal symptoms can last for several weeks to months.

To reduce or prevent withdrawal symptoms, your healthcare provider will lower your clonazepam dose gradually. Tapering can be very gradual over weeks or months to reduce withdrawal symptoms as much as possible.  If you experience any of the following withdrawal symptoms, contact your healthcare provider or seek out emergency medical treatment. Potentially serious withdrawal symptoms include: [10]

  • unusual movements
  • ringing in your ears
  • anxiety
  • memory problems
  • difficulty concentrating
  • sleep problems
  • seizures
  • shaking
  • muscle twitching
  • changes in mental health, depression
  • burning or prickling feeling in your hands, arms, legs or feet
  • seeing or hearing things that others do not see or hear
  • thoughts of harming or killing yourself or others
  • overexcitement or losing touch with reality.

The extended half-life of clonazepam results in a more gradual decline in drug levels, potentially easing withdrawal symptoms compared to shorter-acting benzodiazepines. However, it also means that withdrawal symptoms may take longer to appear.

Considerations When Taking Clonazepam

Clonazepam can have serious side effects and cause withdrawal symptoms. These can be experienced over an extended period because of clonazepam’s long half-life. Use of clonazepam does have a risk of physical dependence even when used as prescribed.

Due to its risk for addiction and serious withdrawal symptoms, clonazepam should be monitored closely by your healthcare provider. If you believe you or someone you know has developed a drug addiction to clonazepam, there are compassionate and effective addiction treatment programs available.

Frequently Asked Questions About Clonazepam Half-Life

What should I do if I miss a dose?

If you miss a dose of this medicine, take it as soon as possible.[11] However, if it is almost time for your next dose, skip the missed dose and return to your regular dosing schedule. Do not double the dose or take extra doses.

How long before Clonazepam helps me feel better?

Clonazepam can help manage your health condition but will not cure it. It may take several days to weeks to feel the full benefit of clonazepam.

I’m experiencing side effects from Clonazepam. Can I just stop taking it?

Do not stop taking clonazepam without first talking to your healthcare provider. If you stop using clonazepam abruptly, you may experience withdrawal symptoms, including new or worsening seizures, hallucinations, behavior changes, sweating, uncontrollable shaking, stomach pain, muscle cramps, anxiety, or sleep difficulties.

Your healthcare provider will work with you to slowly decrease your dose to avoid side effects and withdrawal symptoms, which can range from unpleasant to life-threatening.

Can you overdose on clonazepam?

Yes, you can overdose on clonazepam. Symptoms of an overdose include:[12]

  • Drowsiness or sedation
  • Confusion
  • Impaired coordination or slowed reflexes
  • Respiratory depression
  • Coma and death

A clonazepam overdose can be life-threatening and requires immediate emergency medical attention by calling 911. There is a clonazepam overdose reversal medication called flumazenil, but it must be administered by IV in a hospital setting. Getting medical attention as quickly as possible is imperative during an overdose.

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Amanda Stevens


Amanda Stevens, B.S.

Amanda is a prolific medical content writer specializing in eating disorders and addiction treatment. She graduated Magna Cum Laude from Purdue University with a B.S. in Social Work. Read more

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[1,11] Cleveland Clinic (2024). Clonazepam Tablets. Retrieved from on May 22, 2024.

[2,4] Basit H, Kahwaji CI. Clonazepam. [Updated 2023 May 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan.Retrieved from: on May 22, 2024.

[3,5] (2023). Clonazepam: 7 things you should know. Retrieved from on May 22, 2024.

[7,8,10] (2021). Clonazepam. Retrieved from on May 22, 2024.

[6] DeVane, C.L., Ware, M.R., Lydiard, R.B. (1991). Pharmacokinetics, pharmacodynamics, and treatment issues of benzodiazepines: alprazolam, adinazolam, and clonazepam. Psychopharmacol Bull. 1991;27(4):463-73. PMID: 1687613.

[9,12] (2023). Clonazepam (Klonopin). Retrieved from on May 22, 2024.