The question about half-lives has come up on here before. That's the time it takes for a substance to lose half of its pharmacological activity. The next half-life is half of the first, and so on and so forth until there is a minute fraction left.

This is important to know for washout periods. That's how long it takes for a drug to be completely eliminated. It's important to know when changing drugs that contraindicate each other dangerously. It is also important to know that you need to have a washout period before your next dose of medication if you want to avoid accumulation of the drug in your system.

For some meds you want a steady state, for others, you might not want that. For one thing, accumulation makes it more likely that you will gain tolerance to the drug.

What is a washout period?

"after 5 half lives 96.88% are eliminated
after 10 half lives 99.90% are eliminated
A drug /never/ gets 'completely' eliminated, since we apply the concept
of half lives to a stochastic process"
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I think one reason people have trouble with Ritalin is that its half-life is only 2-4 hours. Assuming a washout period of 5 half-lives, that's 10-20 hours. You could easily have a washout period every night. That could account for the tiredness and not being able to get out of bed that some people feel from it.

Adderall, on the other hand, averages about a 12 hour half life. So 6o hours to be eliminated. Obviously the drug accumulates. There should be less of a crash. And the steady state dose easier to achieve. Also, tapering off it should be easier than quitting Ritalin.

Just my 2 cents!

To make this even more complex :)

Amphetamine's half-life increases during the day as our body's PH naturally shifts from more acidic to less acidic.

BobC

To make this even more complex :)

Amphetamine's half-life increases during the day as our body's PH naturally shifts from more acidic to less acidic.

BobC


Interesting. I've been noticing that my AM dose of adderall IR doesn't do a whole lot for me, but my later dose does. I thought it was just the accumulation or addition of extra adderall into my system, but I think the shift of PH (as you mention) also might play a role. Thanks.

copperpenny,

I think it is the cumulative effects of adding doses later on during the day. Basically this can be a achieved with a therapeutic ir dose

Copperpenny,

Your correct it does accumulate in the system + that is a much stronger effect then the increase in halflife. The increase in halflife basically means dosages in the afternoon last a little longer then dosages in the morning.

BobC