Benzodiazepine Half-Life Chart
Compare how long each benzodiazepine and z-drug stays in the body, using the half-lives in Table 1 of the Ashton Manual.
How long each drug lasts, from Table 1 of the Ashton Manual
Approximate time to clear the body (about five half-lives)
Shortest to longest. shortest figure in the range up to the longest figure. Where Table 1 gives an active metabolite, the bar uses the metabolite.
- Triazolam (Halcion)0.4 days
- Zaleplon (Sonata)0.4 days
- Zolpidem (Ambien)0.4 days
- Zopiclone (Zimovane)1 to 1.3 days
- Eszopiclone (Lunesta)1.3 days
- Alprazolam (Xanax)1.3 to 2.5 days
- Loprazolam (Dormonoct)1.3 to 2.5 days
- Lormetazepam (Noctamid)2.1 to 2.5 days
- Oxazepam (Serax)0.8 to 3.1 days
- Bromazepam (Lexotan)2.1 to 4.2 days
- Lorazepam (Ativan)2.1 to 4.2 days
- Temazepam (Restoril)1.7 to 4.6 days
- Estazolam (ProSom)2.1 to 5 days
- Nitrazepam (Mogadon)3.1 to 7.9 days
- Clonazepam (Klonopin)3.8 to 10 days
- Clobazam (Frisium)2.5 to 13 days
- Quazepam (Doral)5.2 to 21 days
- Halazepam (Paxipam)6.3 to 21 days
- Chlordiazepoxide (Librium)7.5 to 42 days
- Clorazepate (Tranxene)7.5 to 42 days
- Diazepam (Valium)7.5 to 42 days
- Flunitrazepam (Rohypnol)7.5 to 42 days
- Ketazolam (Anxon)7.5 to 42 days
- Medazepam (Nobrium)7.5 to 42 days
- Nordazepam (Nordaz)7.5 to 42 days
- Prazepam (Centrax)7.5 to 42 days
- Flurazepam (Dalmane)8.3 to 52 days
This calculator is an educational planning tool. It is not medical advice and it is not a substitute for supervision by a physician who knows your history. Whether to taper, and how fast, are decisions for you and your prescriber. Never stop a benzodiazepine abruptly.
What does the chart show?
A half-life is the time it takes for the level of a drug in the blood to fall by half. Table 1 of the Ashton Manual, written by Professor C. Heather Ashton, defines it as the time taken for the blood concentration to fall to half its peak value after a single dose, and adds that this time may vary considerably between individuals. That is why most figures in the table are ranges.
Some benzodiazepines are turned by the body into an active metabolite, a second substance that keeps working after the original drug has gone. The Manual shows these in brackets. Diazepam (Valium) has a half-life of 20 to 100 hours, and its active metabolite, desmethyldiazepam, has a half-life of 36 to 200 hours.
The chart estimates how long each drug takes to clear the body by multiplying the longest-acting half-life by five. This is a common rule of thumb in pharmacology, not a figure from the Manual: after five half-lives, about 97 percent of a single dose is gone. The estimates are approximate, and they describe the drug, not how a person feels.
The two are different things. The Manual notes that the duration of apparent action is usually considerably less than the half-life, and that noticeable effects of most benzodiazepines wear off within a few hours. The drug can still be having subtle effects for much longer than that.
Benzodiazepine half-life table
Every figure below comes from Table 1 of the Ashton Manual. The last column applies the five half-life rule of thumb to the longest-acting part of each drug.
| Drug | Brand name in the Manual | Half-life | Active metabolite half-life | Approximate time to clear |
|---|---|---|---|---|
| Alprazolam | Xanax | 6 to 12 hours | none listed | 1.3 to 2.5 days |
| Bromazepam | Lexotan | 10 to 20 hours | none listed | 2.1 to 4.2 days |
| Chlordiazepoxide | Librium | 5 to 30 hours | 36 to 200 hours | 7.5 to 42 days |
| Clobazam | Frisium | 12 to 60 hours | none listed | 2.5 to 13 days |
| Clonazepam | Klonopin | 18 to 50 hours | none listed | 3.8 to 10 days |
| Clorazepate | Tranxene | not listed | 36 to 200 hours | 7.5 to 42 days |
| Diazepam | Valium | 20 to 100 hours | 36 to 200 hours | 7.5 to 42 days |
| Estazolam | ProSom | 10 to 24 hours | none listed | 2.1 to 5 days |
| Flunitrazepam | Rohypnol | 18 to 26 hours | 36 to 200 hours | 7.5 to 42 days |
| Flurazepam | Dalmane | not listed | 40 to 250 hours | 8.3 to 52 days |
| Halazepam | Paxipam | not listed | 30 to 100 hours | 6.3 to 21 days |
| Ketazolam | Anxon | 30 to 100 hours | 36 to 200 hours | 7.5 to 42 days |
| Loprazolam | Dormonoct | 6 to 12 hours | none listed | 1.3 to 2.5 days |
| Lorazepam | Ativan | 10 to 20 hours | none listed | 2.1 to 4.2 days |
| Lormetazepam | Noctamid | 10 to 12 hours | none listed | 2.1 to 2.5 days |
| Medazepam | Nobrium | 36 to 200 hours | none listed | 7.5 to 42 days |
| Nitrazepam | Mogadon | 15 to 38 hours | none listed | 3.1 to 7.9 days |
| Nordazepam | Nordaz | 36 to 200 hours | none listed | 7.5 to 42 days |
| Oxazepam | Serax | 4 to 15 hours | none listed | 0.8 to 3.1 days |
| Prazepam | Centrax | not listed | 36 to 200 hours | 7.5 to 42 days |
| Quazepam | Doral | 25 to 100 hours | none listed | 5.2 to 21 days |
| Temazepam | Restoril | 8 to 22 hours | none listed | 1.7 to 4.6 days |
| Triazolam | Halcion | 2 hours | none listed | 0.4 days |
| Eszopiclone | Lunesta | 6 hours (9 hours in older adults) | none listed | 1.3 days |
| Zaleplon | Sonata | 2 hours | none listed | 0.4 days |
| Zolpidem | Ambien | 2 hours | none listed | 0.4 days |
| Zopiclone | Zimovane | 5 to 6 hours | none listed | 1 to 1.3 days |
The Manual was written for readers in many countries, so the table includes drugs that are not sold in the United States. For equivalent doses between these drugs, use the benzodiazepine conversion calculator.
Why does half-life matter in a taper?
A drug that leaves the body quickly rises and falls between doses. The Ashton Manual explains that with short-acting drugs such as alprazolam (Xanax) and lorazepam (Ativan) it is not possible to achieve a smooth decline in blood and tissue concentrations, and that many people experience a “mini-withdrawal” between doses. This is often called interdose withdrawal.
That is the reason for the diazepam crossover at the heart of the Manual. Diazepam is one of the most slowly eliminated benzodiazepines, so its level in the blood falls gently, and the Manual advises people withdrawing from potent, short-acting drugs to switch to it before reducing. The switch is made one dose at a time, over weeks, with a prescriber.
A long half-life has another effect. The Manual points out that half the active products of a single dose of diazepam can still be in the bloodstream up to 200 hours later, so with daily dosing the drug builds up. After a reduction, the level settles slowly too. That is one reason a dose change can take days to be felt, and why tapers are paced in weeks rather than days.
People who look up half-lives have usually taken a benzodiazepine as prescribed for a long time. Physical dependence is not addiction. It is the body’s expected adaptation to a medicine taken regularly, and it is the reason any change is made gradually.
For more detail, read how diazepam’s long half-life eases interdose withdrawal and how the Ashton Manual diazepam switch works. The Ashton Manual Guide calculator lays out a crossover and reduction in the shape of the Manual’s schedules.
Questions about benzodiazepine half-lives
What is the half-life of a benzodiazepine?
It is the time taken for the level of the drug in the blood to fall to half its peak after a single dose. In Table 1 of the Ashton Manual, half-lives range from about 2 hours for triazolam (Halcion) to 36 to 200 hours for drugs whose active metabolite is desmethyldiazepam. The Manual says the figure may vary considerably between individuals.
What is the half-life of Xanax compared with Valium?
Table 1 gives alprazolam (Xanax) a half-life of 6 to 12 hours. Diazepam (Valium) has a half-life of 20 to 100 hours, and its active metabolite has a half-life of 36 to 200 hours. That difference is why the Manual uses diazepam for the crossover.
How long does diazepam stay in your system?
Using the rule of thumb of five half-lives, diazepam’s active metabolite takes roughly 180 to 1,000 hours, about 7.5 to 42 days, to clear after the last dose. The Manual notes that half the active products of a single dose can still be in the bloodstream up to 200 hours later. These are estimates, and they vary from person to person.
What is interdose withdrawal?
It is withdrawal that appears between doses, as the level of a short-acting drug falls before the next dose is due. The Ashton Manual describes many people on short-acting drugs experiencing a “mini-withdrawal” between each dose, and it recommends switching to a long-acting drug such as diazepam before tapering.
Does a longer half-life mean the effects last longer?
Not directly. The Manual notes that the duration of apparent action is usually considerably less than the half-life, and noticeable effects of most benzodiazepines wear off within a few hours. The drug can still have subtle effects for as long as it is present.
Is the five half-life rule from the Ashton Manual?
No. The half-lives are from Table 1 of the Manual. Multiplying by five is a general rule of thumb in pharmacology, used on this page to turn a half-life into an approximate time to clear the body. After five half-lives, about 97 percent of a single dose is gone.
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