Xanax, Ativan, Valium & Klonopin: How Long They Last
Quick answer: Xanax, Ativan, Valium and Klonopin do not remain in the body for the same amount of time. Alprazolam and lorazepam have mean half-lives around 11–12 hours, clonazepam typically has a 30–40 hour half-life, and diazepam may have a terminal half-life up to 48 hours plus an active metabolite lasting up to 100 hours.
Last updated: September 26, 2026.
Medical review Brandon McNally, RN
Important distinction: Half-life, time to peak concentration, duration of noticeable effects, drug-test detection and withdrawal timing are different concepts. A medication may continue to be present in the body after a person no longer feels its effects, and withdrawal timing cannot be predicted from half-life alone.
Key Takeaways
- Xanax (alprazolam) has a mean elimination half-life of approximately 11.2 hours in healthy adults.
- Ativan (lorazepam) has a mean plasma half-life of approximately 12 hours.
- Klonopin (clonazepam) is considerably longer acting pharmacokinetically, with a typical elimination half-life of 30–40 hours.
- Valium (diazepam) has a terminal elimination half-life of up to approximately 48 hours and produces active metabolites that may persist substantially longer.
- Diazepam's active metabolite N-desmethyldiazepam can have a terminal half-life up to approximately 100 hours.
- Peak concentration is not the same as duration of effect. Xanax and diazepam can reach peak plasma concentrations relatively quickly despite very different elimination profiles.
- Longer half-life can lead to greater accumulation with repeated dosing.
- Withdrawal is a separate clinical issue. See the dedicated benzodiazepine withdrawal guide for withdrawal symptoms and timing.
Table of Contents
- Xanax vs. Ativan vs. Valium vs. Klonopin Duration
- What Does Benzodiazepine Half-Life Mean?
- How Quickly Do These Medications Reach Peak Levels?
- How Long Does Xanax Last?
- How Long Does Ativan Last?
- How Long Does Klonopin Last?
- How Long Does Valium Last?
- Which Benzodiazepine Lasts the Longest?
- Effects vs. Half-Life
- Why Repeated Dosing Changes the Timeline
- What Can Change Benzodiazepine Duration?
- Half-Life vs. Withdrawal Timing
- Does a Longer Half-Life Mean a Stronger Dose?
- Half-Life vs. Drug Testing
- Myth vs. Fact
- When to Seek Medical Help
- Frequently Asked Questions
- Related Clinical Resources
- References
Xanax vs. Ativan vs. Valium vs. Klonopin: Duration at a Glance
The biggest pharmacokinetic difference among these four benzodiazepines is how long they and their metabolites remain in the body. Alprazolam and lorazepam are eliminated more rapidly than clonazepam and diazepam.
| Brand | Generic | Approximate time to peak plasma concentration | Approximate elimination half-life | Key duration feature |
|---|---|---|---|---|
| Xanax | Alprazolam | 1–2 hours | Mean about 11.2 hours | Shorter elimination profile than clonazepam or diazepam |
| Ativan | Lorazepam | About 2 hours | About 12 hours | Major glucuronide metabolite does not have meaningful CNS activity |
| Klonopin | Clonazepam | 1–4 hours | Typically 30–40 hours | Long elimination half-life |
| Valium | Diazepam | Average 1–1.5 hours | Terminal half-life up to about 48 hours | Active metabolite may persist up to about 100 hours |
These numbers describe pharmacokinetics, not a guaranteed number of hours that a person will feel sedated, calm or otherwise affected.
For the broader four-drug comparison of indications, potency, safety and clinical differences, see Xanax vs Valium vs Ativan vs Klonopin: Key Differences.
For approximate dose-equivalency comparisons, see Xanax, Ativan, Valium & Klonopin Equivalency: What Conversion Tables Mean.
What Does Benzodiazepine Half-Life Mean?
A drug's elimination half-life is the approximate time required for its plasma concentration to fall by half. It is a pharmacokinetic measurement, not a direct measurement of how long a person feels the medication.
For example, if a benzodiazepine has a half-life of 12 hours, that does not mean:
- its noticeable effects always last 12 hours;
- the drug is fully eliminated after 12 hours;
- withdrawal automatically begins after 12 hours;
- a drug test becomes negative after 12 hours;
- it is safe to take another sedative after 12 hours.
Elimination generally occurs over multiple half-lives, and repeated dosing can cause accumulation before the previous dose has been fully cleared.
Clinical Pearl: The half-life is most useful for understanding accumulation, dosing intervals and how quickly concentrations decline. It should not be used as a countdown for driving, alcohol use, opioid use, withdrawal onset or drug testing.
How Quickly Do Xanax, Ativan, Valium and Klonopin Reach Peak Levels?
All four oral medications can reach peak plasma concentrations within several hours, despite major differences in how long they are later eliminated.
| Medication | Approximate oral time to peak concentration | What it does not mean |
|---|---|---|
| Xanax / alprazolam | 1–2 hours | It does not mean effects end after two hours |
| Ativan / lorazepam | About 2 hours | It does not establish exact clinical duration |
| Klonopin / clonazepam | 1–4 hours | It does not mean the drug is short acting |
| Valium / diazepam | Average 1–1.5 hours | It does not reflect its very long elimination profile |
A useful example is diazepam: it can reach peak concentrations relatively quickly while still having one of the longest elimination profiles in this group.
How Long Does Xanax Last?
Alprazolam reaches peak plasma concentrations approximately 1–2 hours after an oral dose and has a mean elimination half-life of about 11.2 hours in healthy adults.
The current alprazolam prescribing information reports a half-life range of approximately 6.3–26.9 hours in healthy adults, demonstrating substantial person-to-person variability.
Factors that can prolong alprazolam elimination include age and certain drug interactions affecting CYP3A4 metabolism.
Alprazolam's pharmacokinetic profile is one reason fluctuations between doses and withdrawal symptoms can become clinically important in physically dependent patients.
For withdrawal-specific information, see the dedicated benzodiazepine withdrawal guide.
For questions about Xanax tablet strengths, bars and counterfeit risk, see Xanax Bars: Colors, Strengths, Slang & Risks.
How Long Does Ativan Last?
Oral lorazepam reaches peak plasma concentrations at approximately two hours and has a mean plasma half-life of about 12 hours.
The lorazepam prescribing information reports approximately 90% oral bioavailability and a mean half-life of about 12 hours for unconjugated lorazepam.
Lorazepam is converted primarily to lorazepam glucuronide. That metabolite has a longer plasma half-life of roughly 18 hours but is not considered to have meaningful central nervous system activity.
This metabolic pathway differs from diazepam, which produces pharmacologically active metabolites that can substantially extend its overall pharmacologic presence.
For a broader comparison with Xanax, Valium and Klonopin, see Xanax vs Valium vs Ativan vs Klonopin: Key Differences.
How Long Does Klonopin Last?
Clonazepam is substantially longer lasting pharmacokinetically than alprazolam or lorazepam, with a typical elimination half-life of approximately 30–40 hours.
The clonazepam prescribing information reports that maximum plasma concentrations are reached within approximately 1–4 hours after oral administration.
Its long half-life means clonazepam can remain in the body substantially longer than the period during which a person notices an obvious medication effect.
Repeated dosing can also produce accumulation because another dose may be taken before the previous dose has been fully eliminated.
For approximate Klonopin-to-Valium and Klonopin-to-Xanax potency comparisons, see Xanax, Ativan, Valium & Klonopin Equivalency: What Conversion Tables Mean.
How Long Does Valium Last?
Diazepam has the longest and most complex elimination profile of these four medications because both diazepam and its active metabolites can persist for extended periods.
The diazepam prescribing information reports:
- average time to peak concentration of approximately 1–1.5 hours;
- terminal diazepam elimination half-life of up to approximately 48 hours;
- active metabolite N-desmethyldiazepam half-life of up to approximately 100 hours;
- accumulation with repeated dosing.
Diazepam is also converted to active metabolites including temazepam and N-desmethyldiazepam before further metabolism.
This means the parent drug can begin producing effects relatively quickly while its metabolites continue to contribute to a prolonged pharmacokinetic profile.
Clinical Pearl: Diazepam is a good example of why “fast onset” and “short acting” are not the same thing. A drug can reach peak concentration quickly and still have a very long terminal elimination phase.
Which Lasts Longer: Xanax, Ativan, Klonopin or Valium?
By elimination half-life, clonazepam and diazepam generally persist substantially longer than alprazolam and lorazepam.
A simplified ranking by labeled pharmacokinetic persistence is:
- Valium / diazepam: terminal half-life up to approximately 48 hours, with an active metabolite lasting up to approximately 100 hours.
- Klonopin / clonazepam: typical half-life approximately 30–40 hours.
- Ativan / lorazepam: approximately 12 hours.
- Xanax / alprazolam: mean approximately 11.2 hours.
This is a pharmacokinetic comparison, not a ranking of clinical effectiveness, potency, safety or appropriateness.
Milligram potency is a separate question addressed in Xanax, Ativan, Valium & Klonopin Equivalency: What Conversion Tables Mean.
How Long the Effects Last vs. How Long the Drug Stays in the Body
The duration of noticeable benzodiazepine effects is usually shorter than the full elimination process. A person may no longer feel sedated or noticeably calmer while substantial drug concentrations remain present.
It is useful to separate four timelines:
| Timeline | What it describes | Why it differs |
|---|---|---|
| Onset | When noticeable pharmacologic effects begin | Depends on absorption and formulation |
| Peak concentration | When plasma levels reach their maximum | Measured pharmacokinetically |
| Subjective effect duration | How long the person notices the medication | Depends on dose, tolerance, indication and individual response |
| Elimination | How long the drug and metabolites take to decline | Usually takes multiple half-lives |
Drug-test detection and withdrawal are additional timelines and should not be inferred from the table above.
Why Does Repeated Benzodiazepine Dosing Change the Timeline?
Repeated dosing can cause a benzodiazepine to accumulate when another dose is taken before the previous dose has been fully eliminated.
This phenomenon is particularly relevant to longer-acting drugs such as clonazepam and diazepam.
With repeated use:
- blood concentrations can build toward steady state;
- active metabolites may accumulate;
- sedation may persist longer in susceptible patients;
- elimination after the final dose may take longer than expected from one isolated dose;
- older adults or people with impaired metabolism may experience greater accumulation.
Diazepam labeling specifically notes accumulation with multiple dosing.
This is also one reason a half-life number from a healthy-volunteer study should not be interpreted as an individualized clearance calculator.
What Can Make Xanax, Ativan, Valium or Klonopin Last Longer?
Age, organ function, genetics, repeated dosing and drug interactions can all alter benzodiazepine pharmacokinetics.
Factors that may affect duration or elimination include:
- older age;
- repeated or chronic dosing;
- higher doses;
- liver disease;
- kidney impairment for certain medications or metabolites;
- medications that inhibit or induce drug-metabolizing enzymes;
- individual CYP enzyme differences;
- body composition;
- tolerance and previous benzodiazepine exposure.
Alprazolam and diazepam are particularly affected by CYP-mediated metabolism, while lorazepam undergoes glucuronidation rather than the same oxidative metabolic pathway.
Does a Shorter Half-Life Mean Withdrawal Starts Sooner?
Shorter-acting benzodiazepines can produce more rapid concentration declines, but withdrawal timing cannot be predicted from half-life alone.
Withdrawal depends on factors including:
- dose;
- frequency of use;
- duration of treatment;
- degree of physical dependence;
- the specific benzodiazepine;
- individual metabolism;
- whether the medication was stopped abruptly or tapered.
Alprazolam's relatively short half-life is one reason it can be associated with pronounced fluctuations in physically dependent patients.
Long-acting drugs such as diazepam may have a later onset of withdrawal because concentrations decline more gradually, but withdrawal can still become clinically significant.
For the dedicated withdrawal article, see Benzodiazepine Withdrawal: Xanax vs Ativan vs Valium vs Klonopin.
That article should remain the primary page for symptoms, withdrawal timing, tapering considerations and emergency warning signs; this page should remain focused on pharmacokinetics and duration.
Does a Longer Half-Life Mean a Benzodiazepine Is Stronger?
No. Half-life and potency are separate pharmacologic characteristics.
For example, diazepam lasts much longer pharmacokinetically than alprazolam, yet alprazolam is considerably more potent on a milligram-for-milligram basis.
This is why a comparison cannot simply rank benzodiazepines as “strongest” or “weakest” using one measurement.
Relevant characteristics include:
- relative potency;
- half-life;
- time to peak concentration;
- active metabolites;
- clinical indication;
- individual response.
See Xanax, Ativan, Valium & Klonopin Equivalency: What Conversion Tables Mean for the separate potency and conversion discussion.
Does Half-Life Tell You How Long a Benzodiazepine Will Show on a Drug Test?
No. A medication's half-life can influence detection, but drug-test windows depend on far more than the half-life.
Detection varies with:
- the specimen being tested;
- the specific assay;
- which parent drug or metabolite the assay detects;
- dose;
- frequency of use;
- duration of use;
- individual metabolism;
- laboratory cutoff values.
Diazepam's long-lived metabolites, for example, make its detection profile fundamentally different from a medication without similarly persistent active metabolites.
A separate benzodiazepine drug-testing article should cover urine, blood and other detection windows rather than turning this pharmacokinetic page into a drug-test calculator.
Benzodiazepine Duration: Myth vs. Fact
| Myth | Fact |
|---|---|
| A drug's half-life tells you exactly how long its effects last. | No. Half-life describes plasma elimination, not subjective duration. |
| Xanax is completely gone after about 11 hours. | No. Approximately 11.2 hours is the mean time for plasma concentration to fall by half, not complete elimination. |
| Valium is slow to start because it stays in the body a long time. | No. Oral diazepam can reach peak plasma concentrations in approximately 1–1.5 hours despite its long terminal elimination. |
| Klonopin lasts 30–40 hours because that is its half-life. | The 30–40 hour figure describes elimination half-life, not necessarily the duration of noticeable effects. |
| Ativan and Xanax are basically identical because their half-lives are similar. | No. They differ in metabolism, potency, approved uses and individual clinical response. |
| The longest-lasting benzodiazepine is automatically the strongest. | No. Duration and milligram potency are different characteristics. |
| A half-life can tell you exactly when withdrawal will start. | No. Withdrawal timing depends on dependence, dosing pattern, duration of use and other individual factors. |
When to Seek Medical Help
Emergency evaluation is appropriate for severe CNS depression, overdose symptoms or severe benzodiazepine withdrawal.
Seek urgent or emergency medical care for:
- difficulty breathing;
- very slow or abnormal breathing;
- inability to wake;
- loss of consciousness;
- seizures;
- severe confusion;
- severe agitation or hallucinations after reducing or stopping a benzodiazepine;
- suspected overdose;
- benzodiazepine use combined with opioids followed by marked sedation or breathing problems.
People taking benzodiazepines regularly should not abruptly stop treatment solely because they believe the medication has left their body.
For withdrawal symptoms and timing, see Benzodiazepine Withdrawal: Xanax vs Ativan vs Valium vs Klonopin.
Frequently Asked Questions About Xanax, Ativan, Valium & Klonopin Duration
How long does Xanax last in the body?
Alprazolam has a mean elimination half-life of approximately 11.2 hours in healthy adults, although the reported range is broad. That means the plasma concentration typically falls by half over roughly that period; it does not mean the medication is completely eliminated or that its noticeable effects last exactly 11 hours.
How long does Ativan last in the body?
Lorazepam has a mean plasma half-life of about 12 hours. It reaches peak plasma concentration at approximately two hours after oral administration. Its major glucuronide metabolite persists longer but does not have meaningful central nervous system activity.
How long does Klonopin last in the body?
Clonazepam has a substantially longer elimination half-life than Xanax or Ativan, typically around 30–40 hours. Peak plasma concentrations generally occur within approximately one to four hours after oral administration. Its clinical effects do not necessarily last for the entire half-life.
How long does Valium last in the body?
Diazepam has a terminal elimination half-life of up to approximately 48 hours. Its active metabolite N-desmethyldiazepam can have a terminal half-life up to approximately 100 hours, which is one reason diazepam can accumulate and persist for a prolonged period after repeated dosing.
Which lasts longer, Xanax or Ativan?
Their average parent-drug half-lives are fairly similar: approximately 11.2 hours for alprazolam and about 12 hours for lorazepam. However, they differ in metabolism, potency, indication and individual clinical response, so the half-life alone should not be used to treat them as interchangeable.
Which lasts longer, Xanax or Klonopin?
Klonopin lasts substantially longer pharmacokinetically. Clonazepam has a typical half-life of approximately 30–40 hours, compared with a mean of about 11.2 hours for alprazolam. That does not mean clonazepam is universally more effective or stronger.
Which lasts longer, Klonopin or Valium?
Both are long-acting benzodiazepines. Clonazepam's typical half-life is approximately 30–40 hours. Diazepam has a terminal half-life up to approximately 48 hours and also produces an active metabolite with a half-life up to approximately 100 hours, giving diazepam a particularly prolonged elimination profile.
Does a 12-hour half-life mean the drug is gone in 24 hours?
No. After one half-life, approximately half the drug remains; after another half-life, approximately half of that remaining amount is eliminated. Complete or near-complete elimination therefore takes multiple half-lives and can take longer with repeated dosing or individual metabolic differences.
Does half-life tell you when it is safe to drive?
No. A half-life is not a driving-safety clock. Sedation, coordination, reaction time and cognitive impairment vary between people and doses. A person should follow prescribing instructions and avoid driving or hazardous activities when impaired.
Does half-life tell you when withdrawal begins?
No. Half-life affects the rate at which concentrations fall, but withdrawal timing also depends on dose, frequency, duration of use, physical dependence and whether treatment was stopped abruptly. See the benzodiazepine withdrawal guide for the dedicated discussion.
Does half-life determine benzodiazepine equivalency?
No. Equivalency involves relative potency and clinical response in addition to pharmacokinetics. A longer-acting drug may be less potent per milligram than a shorter-acting one. See Xanax, Ativan, Valium & Klonopin Equivalency: What Conversion Tables Mean.
Can the same benzodiazepine last longer in an older adult?
Yes. Age can substantially alter benzodiazepine pharmacokinetics, particularly for medications with long elimination pathways such as diazepam. Liver function, other medications and repeated dosing can also affect how long a benzodiazepine and its metabolites remain in the body.
Related Clinical Resources
- Xanax vs Valium vs Ativan vs Klonopin: Key Differences
- Xanax, Ativan, Valium & Klonopin Equivalency: What Conversion Tables Mean
- Benzodiazepine Withdrawal: Xanax vs Ativan vs Valium vs Klonopin
- Xanax Bars: Colors, Strengths, Slang & Risks
- Fake Xanax Bars
- Bars Drug Slang
Source Verification
This article was checked against current U.S. prescribing information for alprazolam, lorazepam, clonazepam and diazepam. Pharmacokinetic values describe drug concentration and elimination and are intentionally separated from subjective duration, drug-test detection and withdrawal timing.
The article also separates dose equivalency from pharmacokinetic duration. Approximate benzodiazepine conversion information is addressed in node 71140, while withdrawal symptoms and clinical withdrawal timing are addressed in node 71142.
References
- U.S. National Library of Medicine, DailyMed. Alprazolam Tablets: Prescribing Information .
- U.S. National Library of Medicine, DailyMed. Lorazepam Tablets: Prescribing Information .
- U.S. National Library of Medicine, DailyMed. Clonazepam Tablets: Prescribing Information .
- U.S. National Library of Medicine, DailyMed. Diazepam Tablets: Prescribing Information .
- American Society of Addiction Medicine and partner organizations. Joint Clinical Practice Guideline on Benzodiazepine Tapering . 2025.
Last updated: September 26, 2026.
About the Author
Benjamin Zohar, NCACIP is a Nationally Certified Advanced Clinical Intervention Professional and ISSUP network moderator specializing in addiction intervention, treatment navigation and emerging substance-use risks. His educational work published through ISSUP on counterfeit medications, fentanyl exposure and concentrated 7-hydroxymitragynine has been cited or referenced by GoodRx, The Washington Post, WIRED and Newsweek.
Medical reviewed by Brandon McNally, RN
Medical disclaimer: This article is intended for educational and public-health purposes. It does not provide individualized medical advice, diagnosis or a tapering schedule. Do not start, stop or alter a prescription medication without consulting a qualified healthcare professional. Call emergency services for seizures, difficulty breathing, loss of consciousness, severe confusion or other life-threatening symptoms.