Why does Alprazolam stay in your system for 1-6 weeks when the half-life is always the same?


Why is there so much discrepancy? For example Alprazolam has an average half-life of 11.2 hours, so it should be out of your system in 78 hours. Even in the worst case of 26.9 hours half-life, it should be gone in 188 hours. So why do so many websites say that it’ll be out of your system in 1 to 6 WEEKS?

Sites say that it takes longer for the drug to get out of your body if you are a “regular” user, but why? Seems to me half-life should be the same regardless of whether or not someone is a regular user or not. Once you stop using, the half-life of the drug dictates that it should be out of the system after 188 hours max. So why can it be detected for up to 6 weeks? What is the science behind this?

In: Biology

There are going to be three main reasons for this. First, the half-life of the drug is the time for half the material to break down, meaning there is rare chances for some of the material to last longer than usual. It’s an estimate, not a guarantee.

Second, and more important, is the fact that drugs like Alprazolam break down into secondary products, 4-hydroxyalprazolam and α-hydroxyalprazolam, which themselves can be broken down into other metabolites, before being excreted in the urine.

Like most drugs, the compounds can be deposited into fats or other tissue, leading to a lingering timeline of release, especially when taken over a long period of time.

For example, if you take 1 dose a day, and 1/4 remains in your body after 1 day, then on Day 2 you would have 1.25 dose-equivalents in your body. On Day 3, it would be 1.31, to a limit of 1.333 dose-equivalents in the blood, plus whatever is stored in your tissues.

The third main reason is going to be drug-interaction. Using a CYP3A4 inhibitor, like Tagamet (cimetidine) can delay the intake of Alprazolam into the liver, which would delay the breakdown of the drug, which would allow it to stay in the body longer.

>For example Alprazolam has an average half-life of 11.2 hours, so it should be out of your system in 78 hours.

78 hours is 7 half-lifes, which means there will be ~0.7% remaining. Molecules are very very small, which means a dose of any drug contains a huge number of molecules of that drug. So 0.7% could still be a lot of molecules. What exactly are you defining as “out of your system”? No longer experiencing effects of the drug? Can no longer be detected in a blood test?

If a user is taking a dose every day, and the half-life is 11.2 hours, that means there’s still ~25% remaining from the previous dose when the new dose is taken, so over time the amount in the system will increase. This probably why it says it takes longer for a regular user.

Let’s say a dose is 100 of some abstract unit. Day 1 you have 100 units. On Day 2, you are down to 25 then take the second dose so you’re up to 125. That means Day 3 you’ll be down to 31.25 units and so the third dose will take you to 131.25, and so on.