All drugs have a Half Life which is the time the drugs loose it's value--generally by half. My Blood Thinner Xarelto for example has a half life of nine hours.
@Lon Tanner This is a concept which should be made part of the understanding of medication usage for every single user, yet, I've found few not having a technical background grasp the meaning,or the significance. As a medication works it's way through a person's system, it is gradually eliminated by the body. Some meds "last" longer in the body than others do. So, the idea of "half-life" is used. Half life is the LENGTH OF TIME NEEDED FOR THE BODY TO ELIMINATE 1/2 of the medication taken. After taking the med, the quantity of it in the bloodstream increases, levels off, then begins to drop. In order to maintain a good working level of it in the system, and additional dose is prescribed to be taken sometime before the "drop off" becomes significant. After a number of doses thus administered, the system experiences a certain average level of medication, as more is added while more is removed. This is known as "blood level concentration". BLC is an important consideration especially in the use of antibiotics to clear up infections. Frank
It can get very complicated, but @Frank Sanoica's explanation is a good one. Some drugs have active metabolites which also must be monitored. There are also "compartment models" which affect the length of time for a drug to reach steady state. That is why you sometimes see a "loading dose" given to get to therapeutic levels more quickly. Oh, @Lon Tanner since you are critical of grammar, you should have used "lose" instead of "loose".
All true----Many people think that if they miss one dose of their drug it will kill them or make them ill. NOT SO! Them some people will think if they double up after missing a dose that will make up for it. BAD IDEA!
As long as we're gonna jump on that train, "it's" is a contraction for "it is," while "its" is the possessive form of the noun. Lon should have said "lose its value," not "loose it's value."
The half-life of any substance that experiences mass decay is only the time required for half of it to decay...but remember...the other half must decay too, and the remaining half of that, and so on until it's all gone, which may require hundreds of half-lifes! Hal