Halfway through a stack of short-loan books


in Daily updates, Oxford

Happy Birthday Christina Porte

After a foggy day of reading, I have decided that I cannot efficiently carry out the tasks of graduate student life in the absence of caffeine. As such, I am lifting my personal prohibition, while being mindful of the three to four hour half-life (λ) of caffeine and my continuing efforts to develop a stable and efficient sleep pattern.

On an interesting side note, the half-life of caffeine (the time it takes for half of the concentration initially in the blood to be metabolized) varies enormously on the basis of certain factors:

λ for caffeine, normal adults: 3-4 hours
λ for caffeine, adult women taking oral contraceptives: 5-10 hours
λ for caffeine, pregnant women: 9-11 hours

For those with longer half-lives, the effect of the drug will be less marked, but will last for dramatically longer. [Update: This may be wrong. See this comment.] To quote Lisa Simpson:

As intelligence goes up, happiness goes down. See, I made a graph…”


“…I make a lot of graphs.”

With an eleven hour half-life, you would still have about one quarter of the caffeine from the previous morning’s coffee in your blood as you sat down with the next morning’s brew. With a three hour half-life, less than half a percent of the caffeine from the previous day would still be present.

On a related note, Green’s Café is no longer being seriously considered as a thesis HQ, because it closes far too early. Instead, I am working in the Jericho Café. They are open until a rather more useful 9:30pm. They are also closer to my house, and have a wider collection of food available. Thankfully, I am on track to have my reading for this week’s developing world seminar done by then; that means that I will not have to worry about it when I go to London on Wednesday.

{ 5 comments… read them below or add one }

Anonymous November 6, 2006 at 5:07 pm

Five whole days from renouncing caffeine to re-embracing it. Not bad, for a student.

Milan November 6, 2006 at 5:12 pm

Say what you will about dependence, I have read more since lifting the embargo than in the three days prior. This is the kind of pace that is required in order to stay abreast of the seminar while also working on the thesis.

Milan November 6, 2006 at 11:32 pm

A very good point.

“The principal mode of action of caffeine is as an antagonist of adenosine receptors in the brain. The caffeine molecule is structurally similar to adenosine, and binds to adenosine receptors on the surface of cells without activating them (a “false transmitter” method of antagonism). The reduction in adenosine activity results in increased activity of the neurotransmitter dopamine, largely accounting for the stimulatory effects of caffeine.”

“Caffeine is metabolized in the liver by the cytochrome P450 oxidase enzyme system.”

Since the two seem independent, I would guess that your hypothesis about the effect of the slower half life is correct.

(Source – also for the original data on half lives)

Milan November 7, 2006 at 12:13 am

Tristan has his own distillation of the above post on his blog.

R.K. November 6, 2006 at 11:19 pm

For those with longer half-lives, the effect of the drug will be less marked, but will last for dramatically longer.

This is only true if the chemical reactions wherein caffeine makes you more awake (or whatever else it does mentally) are the same as the ones that destroy it. If the two are seperate, it could have just as big an effect, but for a much longer time.

Imagine you have little spiky balls in your blood, poking holes in your arteries. Now, imagine your kidneys slowly destroy the balls. The amount of damage done would be constant per unit of concentration and time, regardless of the rate at which they are being eliminated.

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