Energy drinks before training: what they actually do, and what they do not

An energy drink before training does one thing well: it delivers caffeine in a liquid you can drink fast. Everything else on the label — taurine, B vitamins, guarana, amino acids — is either dosed too low to notice or has no clear effect on strength and endurance. So the question is not whether energy drinks work, but whether you need caffeine in that particular package.

What is actually in the can

A standard 250 ml can holds about 80 mg of caffeine and about 27 g of sugar. The 500 ml can doubles it: roughly 160 mg of caffeine and 54 g of sugar, which is about 13 sugar cubes and 215 kcal. Sugar-free versions carry the same caffeine and under 10 kcal.

For scale:

• 30 ml espresso: 60–80 mg caffeine
• 250 ml filter coffee: 90–120 mg
• 250 ml black tea: 40–50 mg
• caffeine tablet: usually 100 or 200 mg

So a big can is roughly two coffees, and a small can is one weak coffee. Nothing exotic is happening.

How much caffeine you actually need

The dose that consistently helps performance in studies is 3–6 mg of caffeine per kilogram of body weight, taken 45–60 minutes before training. In practice:

• 60 kg: 180–360 mg
• 70 kg: 210–420 mg
• 80 kg: 240–480 mg
• 95 kg: 285–570 mg

The top half of that range rarely buys anyone anything extra. Most people get nearly the full effect at 2–3 mg/kg, and above that you are mostly paying in jitters and wrecked sleep. An 80 kg lifter lands at 160–240 mg, which is one large can, or a small can plus a coffee.

What to expect, realistically: about 1–2 extra reps on a set you would normally take to 8–10, better focus on the last two sets, and the same load feeling lighter. It is a few percent, and you notice it most when you are underslept or training after a full workday.

When to drink it

Blood caffeine peaks 30–60 minutes after you drink it, so the rule is simple: drink it 45 minutes before your first working set, not in the locker room. The half-life is 4–6 hours, up to 8 in some people, and that is the part everyone underestimates.

Concrete example: you train at 19:00 and drink a 500 ml can (160 mg) at 18:15. At 23:00 when you go to bed, you still have roughly 80–100 mg on board — about the same as drinking a coffee at bedtime. Hence the rule: no caffeine in the last 8 hours before sleep. If you train late, an energy drink costs you more in sleep than it gives you in the gym.

Sugar: when it helps, when it just adds calories

The 27 g of carbs in a small can makes sense if you train longer than 60–75 minutes, if you train fasted in the morning, or if your last meal was 5 hours ago. For a standard 45–60 minute strength session after a normal lunch, you do not need it — that is 110 kcal you did not plan for.

If you are tracking calories or in a deficit, take the sugar-free version. If you genuinely need fuel, 30–40 g of carbs from a meal 90 minutes earlier does the job better.

Taurine, B vitamins, guarana

Taurine is usually dosed at 1000 mg per 250 ml. Evidence that it changes strength or endurance on its own is weak and inconsistent; it is not harmful, but it is not a reason to buy. B vitamins (typically 16 mg niacin, 2 mg B6, some B12) do not give you energy unless you are genuinely deficient — they cover a daily requirement, nothing more.

Guarana matters for a different reason: it is a caffeine source, and manufacturers sometimes list it separately. If the label shows both caffeine and guarana, the real total is higher than the number printed next to the word caffeine. Always read total mg per can, not per 100 ml.

Where energy drinks genuinely fall short

• Tolerance. After 2–3 weeks of daily use, most of the alertness effect fades and what remains is dependence plus a headache on the days you skip.
• Dosing. A can is a fixed unit. You cannot take 60% of it the way you can with a tablet or a coffee.
• Upper limit. For healthy adults, up to 400 mg per day and up to 200 mg in a single dose is the usual reference point. Two large cans plus two coffees already puts you over it.
• Side effects. Hand tremor ruins your bar path on squats and deadlifts, an elevated heart rate is annoying on conditioning work, and for anxious people 200 mg can produce three hours of restlessness.

A practical plan

1. Use them 2–3 times per week, only for your hardest sessions, not every day.
2. Start with a small can (80 mg) or half a large one and see how you react before jumping to 200 mg.
3. Drink it 45 minutes before training, with 300–500 ml of plain water alongside.
4. Never within 8 hours of bedtime.
5. Every 8–10 weeks, take a 7–10 day break to reset sensitivity. Expect a headache and sluggishness for the first 2–3 days.

Who should skip them

Anyone under 18, pregnant or breastfeeding people (the limit is 200 mg of caffeine per day from all sources), anyone with uncontrolled high blood pressure, a known arrhythmia or heart condition, people on thyroid medication, stimulants or certain antidepressants, and anyone who gets panic attacks. Mixing them with alcohol is a specifically bad idea because it masks how drunk you are.

When to see a doctor

• chest pain or pressure during or after training, with or without an energy drink
• a skipping or pounding heartbeat that lasts more than a few minutes at rest
• fainting, dizziness or nausea that keeps coming back
• resting blood pressure consistently above 140/90 across several readings on different days
• insomnia lasting more than 3 weeks even after you cut afternoon caffeine

If you already have a diagnosed heart condition, high blood pressure, or take regular medication, ask your doctor before adding any stimulant, not after.

The short version

• The only ingredient that reliably works is caffeine: 80 mg in a 250 ml can, 160 mg in a 500 ml can.
• Aim for 2–3 mg per kilogram of body weight, 45 minutes before training; more than that mostly buys jitters.
• The effect is real but modest: 1–2 extra reps per set and a lower sense of effort.
• No caffeine in the last 8 hours before sleep — lost sleep erases the benefit.
• Use them 2–3 times a week with a 7–10 day break every two months; coffee and sugar-free versions do the same job for less money and fewer calories.