Caffeine is one of the few sports supplements where the evidence is not in dispute. The International Society of Sports Nutrition has a position stand on it. It works.

What people get wrong is not whether to use it. It is how much, and when.

The dose the research supports

Caffeine has consistently improved exercise performance at doses of 3 to 6mg per kilogram of body mass.

Run your own number:

Two things jump out of that table.

First, the upper end collides with general population health guidance. Food Standards Australia New Zealand puts the safe daily ceiling at 400mg for healthy adults, and flags that single doses above roughly 210mg are associated with raised blood pressure and anxiety. A 90kg athlete taking 6mg/kg is at 540mg in one sitting. That is a specialised athletic protocol, not everyday advice.

Second, and far more useful for most people: the low end works. There is good evidence that 1 to 3mg/kg is about as effective as the higher doses. And a study in young female team-sport athletes found 6mg/kg outperformed both 3mg/kg and 9mg/kg — the highest dose was worse, not better.

Very high doses of caffeine, around 9mg/kg, come with a high rate of side effects and do not appear to be necessary to get the performance benefit.

If you are new to this, start at 2 to 3mg/kg. For most people that is 150 to 200mg — roughly two coffees, not a scoop of something neon.

Timing

Caffeine takes 30 to 90 minutes to reach peak plasma concentration, averaging around 45 minutes. The most commonly used protocol in the research is 60 minutes before exercise.

Taking it as you walk into the gym means your working sets are happening on the way up rather than at the top. Take it before you leave the house.

What it actually improves

The benefits are real but they are not uniform:

• Aerobic endurance — the most consistent effects, moderate to large
• Muscular endurance — small to moderate, reliably reproduced
• Strength and movement velocity — small to moderate
• Sprinting, jumping, throwing — small to moderate

Individual response varies a lot. Some of it is genetic — how fast you metabolise caffeine is partly determined by liver enzyme variation. If caffeine has never done much for your training, that may simply be true for you.

The calorie question

Worth a mention, because pre-workout calories are the ones people forget to count.

A large sugary energy drink can run 150 to 250 calories before you have lifted anything. A sweetened iced coffee can be worse. If you are training to change body composition, drinking a third of a training session back on the way to the gym is a strange trade.

Black coffee is close to zero, which is why it remains the cheapest good option. Beyond that, it is worth checking the panel rather than assuming.

Where it backfires

Evening training. This is the big one. Caffeine has a half-life of around five hours. Take 150mg before a 6pm session and you still have roughly 75mg on board at 11pm. You will train well and sleep badly, and the sleep debt costs you more than the session gained. For anything after mid-afternoon, drop the dose hard or skip it.

Stacking without counting. A pre-workout scoop, a morning coffee and an energy drink is easily 500mg before you have touched a barbell.

Tolerance creep. Regular high doses blunt the effect, and the usual response is to take more. Cycling down periodically restores the response better than escalating does.

Fasted training with a large dose. Absorption is faster on an empty stomach, which sharpens both the benefit and the jitters.

A practical protocol

1. Work out 2 to 3mg/kg for your body weight. That is your starting dose.
2. Take it 60 minutes before you train.
3. Count everything else caffeinated you have had that day, and stay under 400mg in total.
4. If you train after 3pm, drop the dose hard or skip it.
5. Give it a few sessions before you change anything. More is not the default answer.

Where Sour Smacker comes in

A pack of Sour Lemon or Sour Peach is 150mg of natural caffeine plus 100mg of natural L-theanine — ten gummies, one serving, one pack a day.

Against the table above, 150mg lands in the starting band for most adults: around 3mg/kg at 50kg, 2.5mg/kg at 60kg, a shade over 2mg/kg at 70kg. That is inside the 1 to 3mg/kg range the research says performs about as well as the heavier protocols, without the side-effect load.

On the calorie point, a pack is 90 calories and 2g of sugar, with no sugar alcohols. Take it 60 minutes out, in the car park or before you leave the house.

Practically, the advantage over a scoop or a can is that a pack is a fixed, known, portable dose. It does not go flat, it does not need a fridge, and it survives being sat on in a gym bag.

For daily limits and why the crash happens, see our guide to how much caffeine is too much. The ingredient side is in what the research says about L-theanine and caffeine.