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Article Summary

Benzodiazepines

Question:

What are the main differences between different benzodiazepines?
What is the duration of effects (half life) of Valium, Sobril, Xanax, Xanor, Mogadon, Rohypnol, etc.?

Answer:

Potency

A large number of benzodiazepines are available. There are major differences in potency between different benzodiazepines, so that equivalent doses vary as much as 20-fold. For example, 0.5 milligrams (mg) of alprazolam (Xanax) is approximately equivalent to 10mg of diazepam (Valium). Thus a person on 6mg of alprazolam daily, a dose not uncommonly prescribed in the US, is taking the equivalent of about 120mg of diazepam, a very high dose. These differences in strength have not always been fully appreciated by doctors, and some would not agree with the equivalents given here. Nevertheless, people on potent benzodiazepines such as alprazolam, lorazepam (Ativan) or clonazepam (Klonopin) tend to be using relatively large doses. This difference in potency is important when switching from one benzodiazepine to another, for example changing to diazepam during withdrawal, as described in the next chapter.

Speed of elimination

Benzodiazepines also differ markedly in the speed at which they are metabolised (in the liver) and eliminated from the body (in the urine). For example, the "half-life" (time taken for the blood concentration to fall to half its initial value after a single dose) for triazolam (Halcion) is only 2-5 hours, while the half-life of diazepam is 20-100 hours, and that of an active metabolite of diazepam (desmethyldiazepam) is 36-200 hours. This means that half the active products of diazepam are still in the bloodstream up to 200 hours after a single dose. Clearly, with repeated daily dosing accumulation occurs and high concentrations can build up in the body (mainly in fatty tissues). There is a considerable variation between individuals in the rate at which they metabolise benzodiazepines.

Benzodiazepines 5
Half-life (hrs) 1
[active metabolite]
Market Aim 2
Approximately Equivalent
Oral dosages (mg) 3
Alprazolam (Xanax, Xanor)
6-12
a
0.5
Bromazepam (Lexotan, Lexomil)
10-20
a
5-6
Chlordiazepoxide (Librium, Tropium)
5-30 [36-200]
a
25
Clobazam (Frisium)
12-60
a,e
20
Clonazepam (Klonopin, Klonapin, Rivotril, Liktorivil)
18-50
a,e
0.5
Clorazepate (Tranxene)
[36-200]
a
15
Diazepam (Valium, Apzepam, Stesolid)
20-100 [36-200]
a
10
Estazolam (ProSom)
10-24
h
1-2
Flunitrazepam (Rohypnol, Fluscand)
18-26 [36-200]
h
1
Flurazepam (Dalmane)
[40-250]
h
15-30
Halazepam (Paxipam)
[30-100]
a
20
Ketazolam (Anxon)
2
a
15-30
Loprazolam (Dormonoct)
6-12
h
1-2
Lorazepam (Ativan, Temesta)
10-20
a
1
Lormetazepam (Noctamid)
10-12
h
1-2
Medazepam (Nobrium)
36-200
a
10
Nitrazepam (Mogadon, Apodorm)
15-38
h
10
Oxazepam (Serax, Serenid, Serepax, Sobril, Oxascand)
4-15
a
20
Prazepam (Centrax)
[36-200]
a
10-20
Quazepam (Doral)
25-100
h
20
Temazepam (Restoril, Normison, Euhypnos)
8-22
h
20
Triazolam (Halcion)
2
h
0.5
Non-benzodiazepines with similar effects 4 , 5
Half-life (hrs) 1
[active metabolite]
Market Aim 2
Approximately Equivalent
Oral dosages (mg) 3
Zaleplon (Sonata)
2
h
20
Zolpidem (Ambien, Stilnoct)
2
h
20
Zopiclone (Zimovane, Imovane, Zopiklon)
5-6
h
15

  1. Half-life: time taken for blood concentration to fall to half its peak value after a single dose. Half-life of active metabolite shown in square brackets. This time may vary considerably between individuals.
  2. Market aim: although all benzodiazepines have similar actions, they are usually marketed as anxiolytics (a, tranquilizers), hypnotics (h, sleeping pills) or anticonvulsants (e, reducing epileptic seizures or convulsions).
  3. These equivalents do not agree with those used by some authors. They are firmly based on clinical experience but may vary between individuals.
  4. These drugs are chemically different from benzodiazepines but have the same effects on the body and act by the same mechanisms.
  5. All these drugs are recommended for short-term use only (2-4 weeks maximum).

Duration of effects

The speed of elimination of a benzodiazepine is obviously important in determinisizeng the duration of its effects. However, the duration of apparent action is usually considerably less than the half-life. With most benzodiazepines, noticeable effects usually wear off within a few hours. Nevertheless the drugs, as long as they are present, continue to exert subtle effects within the body. These effects may become apparent during continued use or may appear as withdrawal symptoms when dosage is reduced or the drug is stopped.

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