Three things to remember are that dosage, timing and your individual tolerance to caffeine are all key to using it during a triathlon. Research suggests 2-6mg per kg of bodyweight is the optimal range for most endurance athletes. Less is unlikely to have an effect; any more could prompt adverse side effects.
The ‘sweet spot’ is quite individual, but starting with around 2-3mg/kg is a good ballpark figure. Ideally you should use the lowest dose that delivers a decent response. For this reason, using products like tablets, drinks or energy gels with exact quantities of caffeine is preferable to just guessing your dosage.
Caffeine takes around 45-60mins to peak in the bloodstream after consumption. It’s absorbed via the stomach and intestines with effects lasting about 3hrs. This means that for shorter sprint and Olympic races, taking a dose 1hr before swim start is ideal and you shouldn’t need more during your race. For middle, long or ultra races, a similar 60min pre-start dose can be followed up with a drip feed approach during the race. This can provide a welcome boost when you’re starting to flag and the initial hit wears off.
From a genetic point of view, people’s bodies process caffeine with different levels of effectiveness. Some handle it well, while others get the ‘jitters’. Your day-to-day caffeine habits affect tolerance, too, so you need to know how your body handles it before using on race day. If you’re a regular coffee drinker, abstaining or cutting back 5-6 days before your race can increase potency quite dramatically. Just be aware that going fully ‘cold turkey’ can bring on headaches and other withdrawal symptoms if you’re a regular user, so it’s probably best to step down consumption over a few days rather than just stopping overnight.