I am a regular caffeine drinker. I try to regulate my intake to 4 caffeinated drinks a day (with a large coffee shop coffee counting as 2), although at times of work stress that can increase to 5 - 8. On most Audax events I can't source that level of intake - Coke gives me stomach cramps, reflux, hiccups, etc - and so 8 - 12 hours into the ride I start to suffer from caffeine withdrawal - my power output goes down, I get the dozies, and feel generally dreadful. At night multiply these symptoms by 2.
Since the Moor Like a 400, which I abandoned halfway round because of the above (in 2005), I've adopted a principle of caffeine abstention before a big ride (over 300km). The results have nearly always been positive. I've experimented with different lengths of abstention (4 weeks before PBP2007) down to 4 days for last weekend's Porkers. And it works for me. (The few times I haven't abstained have correlated with below par efforts).
A couple of things I have learnt. It help to go down to half measures for the first couple of days - ie 2 drinks. I will suffer headaches and listlessness for a couple of days, but because I know why they're manageable (and perhaps easier to cope with on the 30th repetition of a caffeine fast). A week is long enough. That first coffee is like rocket fuel. So use it wisely. But I'll often have a tea at the start of the ride. The tea is more slow release than the coffee, which can have a peak and crash (like a Mars bar has with sugar), and Red Bull and similar drinks don't work for me - a huge spike and almighty low afterwards.
