Half Lives and Why They Matter
The main difference between the various benzodiazepines is the length of time they are active in the body. This is measured by the half-life of each drug.
“The duration of action of a drug is known as its half life. This is the period of time required for the concentration or amount of drug in the body to be reduced by one-half. We usually consider the half life of a drug in relation to the amount of the drug in plasma.”
In other words, the half-life of a drug is the time it takes for it to be reduced by half. This will depend on many factors, including how the body processes and gets rid of the drug, and can vary from a few hours to a few days. The half-life given for any drug is not an exact figure and, in reality, it can vary from person to person.
A drug's half-life matters because for many, a shorter half life might mean less withdrawal issues, i.e:
a short half-life = increased withdrawal symptoms
a long half-life = less withdrawal symptoms
Short-acting meds have a short half life. For example, Xanax has a half life of 6-12 hours.
This means is the medication is processed quickly and leaves your body more quickly. These can carry a greater risk of withdrawal symptoms because your body has less time to heal and adapt to working without the drug. These short acting drugs carry a higher risk of the user developing interdose withdrawal.
Long-acting meds have a long half-life. For example, Valium has a half life of up to 200 hours.
This means that the medication is processed by your body more slowly and takes longer to leave your body. Some find that moving a short half-life benzo to a long half-life one, makes for a much smoother taper and withdrawal, but not everyone can tolerate the transition to the other medication and they find they need to taper directly off the short acting benzo.
This is due to something called interdose withdrawal which is when someone may be experiencing withdrawal symptoms in between doses. For meds with a longer half life this is less likely.
Understanding the half life is critical to planning your taper so you can minimise withdrawal symptoms.
If you look online you will find there are no clearly defined equivalencies for benzodiazepines. We have chosen to publish the numbers from the work done by Professor Ashton who has helped over 300 people withdraw from these medications using her protocol.
Examples of BEnzos and Half Lives (hours)
Alprazolam 9 – 20
Bromazepam 8 – 30
Chlordiazepoxide 24 – 100
Clonazepam 19 – 60
Clorazepate 1.3 – 120
Diazepam 30 – 200
Estazolam 8 – 24
Flunitrazepam 18 – 26
Flurazepam 40 – 250
Halazepam 30 – 96
Ketazolam 30 – 200
Lorazepam 8 – 24
Lormetazepam 10 – 12
Nitrazepam 15 – 48
Oxazepam 3 – 25
Prazepam 30 – 100
Quazepam 39 – 120
Temazepam 3 – 25
Triazolam 1.5 - 5
Planning your taper will involve looking at your medications half life. If you are on a drug with shorter half life, you may need to dose multiple times a day, while a long half life drug may only need to be taken once a day.
This short animation explains the concept of a half life nicely.