Reality of drug half life?

[FreebaseCogita]

Consider Alprazolam as an example. It has a stated half life of around 12 hours. If I took 1mg at 00:00 would I feel the same effects as having taken 0.5mg at +12:00, 0.25mg at +24:00 and so on?

 

[bloodshed344]

No. Half-life and duration of effects are not as correlated as you might think.

 

[QUARE]

Half-life by definition is the time it takes for a substance to lose half of its pharmacological property but that doesnt include the metabolite and other factor that may change the total duration of the drug.

 

[Lightning-Nl]

Half-life by definition is the time it takes for a substance to lose half of its pharmacological property but that doesnt include the metabolite and other factor that may change the total duration of the drug.

That's correct.

Chemicals that are not active themselves, technically have a negative half-life. One such instance would be lisdexamfetamine. LisdexAMP is a prodrug to Dextroamphetamine and is not active itself. Therefore, it has to be metabolized into the active drug in order for it to work.

Technically, it's impossible for something to have a negative half-life, as it's not possible for something to break down before it's even active, however, in terms of pharmacological action; that's the way I think of it.

Also, it should be noted that the word Half-Life means something different in chemistry. A half-life in pharmacology is how long it takes for the body to break down the main ingredient of a drug so it becomes inactive. A half-life in chemistry refers to the amount of time it takes for a substance to natrually decay to the point of being unstable. Instability then causes the compound to break apart and disband, thus becoming something else entirely.