Relentlessに含まれるカフェイン量はどれくらい？

A 500 ml can of Relentless energy drink contains 160 mg of caffeine.

That works out to 32 mg of caffeine per 100 ml, making it moderately concentrated among carbonated energy drinks. For comparison, a standard 240 ml cup of drip coffee provides about 96 mg of caffeine (USDA FoodData Central), so one Relentless delivers roughly the caffeine of 1.7 cups of coffee. The U.S. Food and Drug Administration (FDA) considers 400 mg a day an amount not generally associated with dangerous, negative effects for healthy adults — this can represents 40% of that daily guidance. Caffeine from a liquid dose like an energy drink is typically absorbed within 30–60 minutes, with effects noticeable as early as 15 minutes after consumption.

Relentless also includes taurine, B vitamins, and glucuronolactone common to many energy drinks, but its stimulant action is primarily driven by caffeine. The 160 mg dose sits in the middle of the energy-drink spectrum: more than a 250 ml Red Bull (80 mg) but less than a 473 ml Bang or Reign (300 mg each). This makes it a moderate option for someone seeking alertness without approaching the entire daily limit in a single can.

Relentlessが体内にどれくらい残るか

How Long Does 160 mg of Caffeine Stay in Your System?

Caffeine follows first-order elimination kinetics, with a population-average half-life of 5.7 hours. This means that every 5.7 hours, the amount remaining in your body drops by half. Starting with a 160 mg dose from a can of Relentless, you can calculate the approximate residual at key time points using the formula: remaining = 160 × 0.5^(hours / 5.7). For a personalized decay timeline, see the caffeine half-life calculator.

After 3 hours, about 111 mg remains (160 × 0.694). After 6 hours — roughly the span from an early afternoon pick-me-up to early evening — around 77 mg is still present (160 × 0.482). By 9 hours post-consumption, the residual is approximately 54 mg (160 × 0.335), and after 12 hours it declines to about 37 mg (160 × 0.232). These numbers are averages; individual metabolism varies with genetics, liver function, pregnancy, and other factors. For a person who drinks a Relentless at 3:00 PM (15:00), more than 70 mg of caffeine would remain in circulation at 9:00 PM, which is comparable to the caffeine in a small cup of coffee. That late-day caffeine load can delay sleep onset and reduce deep sleep, even if the person does not feel overtly stimulated (Drake et al., Journal of Clinical Sleep Medicine, 2013).

When Should You Drink a Relentless to Stay Within Safe Limits?

The FDA’s 400 mg daily caffeine guidance for healthy adults means you can consume up to two and a half 500 ml cans of Relentless without formally exceeding the limit — two cans deliver 320 mg, leaving room for a small cup of tea, while three cans would reach 480 mg and surpass the recommendation. For most people, keeping intake below 400 mg spread across the day is a sensible habit. If you are pregnant, the European Food Safety Authority (EFSA) sets a stricter maximum of 200 mg per day, making even a single can of Relentless account for 80% of that cap and leaving little room for other caffeine sources.

Sleep disruption is another factor. Caffeine’s long half-life means that a dose taken in the afternoon can linger well into the night. With a bedtime of 23:00, a Relentless consumed at 15:00 leaves roughly 60 mg of caffeine still active at 23:00 — an amount similar to a weak cup of instant coffee, which can delay sleep onset and reduce deep sleep (Drake et al., Journal of Clinical Sleep Medicine, 2013). Pushing consumption earlier to noon (11 hours before bed) reduces the bedtime residual to about 44 mg. To find your personal cut-off time based on body weight and sensitivity, use our latest cup before bedtime calculator.

How Does Relentless Compare to Other Energy Drinks and Coffee?

Relentless delivers 160 mg of caffeine in its 500 ml can, placing it in the middle of the energy-drink market. It contains exactly the same amount as a 473 ml can of Monster Energy, Rockstar, and NOS — all of which clock in at 160 mg per can. It is substantially lower than the high-caffeine entrants: a 473 ml can of Bang or Reign provides 300 mg, nearly double the Relentless dose. Celsius and Prime Energy (both 355 ml) contain 200 mg, while the 250 ml original Red Bull offers just 80 mg, and the larger 355 ml Red Bull has 114 mg. For a complete ranking, see our comprehensive energy drink caffeine chart.

Against coffee, Relentless holds its own in a different format. A typical 240 ml cup of drip coffee averages 96 mg (USDA FoodData Central), so this 500 ml can is equivalent to about 1.7 cups. An espresso shot (30 ml) usually contains around 63 mg, making Relentless about 2.5 times stronger than a single shot, but less potent than many large-size coffeehouse brews, which can surpass 200 mg. If you are more familiar with tea, the same volume of green tea (240 ml) has only 28 mg — Relentless packs nearly six times that. For a side-by-side visual comparison, try our caffeine drink comparison tool.

Relentlessの数値を左右する要素

Does the Caffeine in Relentless Vary by Flavor or Can Size?

The 160 mg figure comes from the nutrition labelling on a standard 500 ml can of Relentless Original. Across the core lineup — including Relentless Tropical, Relentless Berry, and Relentless Zero Sugar — the caffeine content is identical: 160 mg per 500 ml. The manufacturer formulates all these variants with the same caffeine concentration, so switching flavors does not change your intake.

Unlike coffee, where brewing method and bean type create wide swings in caffeine, Relentless is a factory-blended product with tight specification controls. Each batch is mixed to a target of 0.032% caffeine, which for a 500 ml fill delivers 160 mg. Minor production variations are possible — regulatory guidelines often permit nutrient values within 20% of the label (Code of Federal Regulations Title 21, §101.9) — but independent testing by public health agencies rarely finds energy drinks deviating far from their declared content. If you are relying on the 160 mg number for dietary planning, you can treat it as a reliable estimate.

No decaffeinated version of Relentless exists. If the same brand ever launches a smaller can size, the caffeine content would scale proportionally with volume, assuming the same recipe. For now, the only widely available format is the 500 ml can, making 160 mg the consistent dose.

この数値の出典

Where Does the 160 mg Number Come From?

The caffeine content of Relentless is declared on the can’s nutrition facts panel, as required by food labelling regulations. The manufacturer lists 160 mg per 500 ml serving, which complies with the European Union’s maximum for energy drinks of 32 mg per 100 ml (Directive 2002/67/EC). This value is a total that includes caffeine from added caffeine and from natural sources like guarana extract. We cross-reference this with entries in public databases such as the USDA FoodData Central, though energy drinks often appear under varying brand names and reformulations can lag behind label updates.

Published values may disagree because some older databases reference smaller can sizes or earlier formulations. When we find conflicting figures, we verify against the current product label and manufacturer website. If a recipe change occurs — for example, a new production batch with a different caffeine concentration — we update the number here. This page is part of the open caffeine dataset that powers TrackCaffeine. If you see a number that looks wrong against a freshly purchased can, you can submit a correction through the dataset.

結論

Bottom Line

A single 500 ml can of Relentless energy drink provides 160 mg of caffeine, which is 32 mg per 100 ml and 40% of the FDA’s suggested daily maximum of 400 mg for healthy adults. That is equivalent to approximately 1.7 cups of standard drip coffee (96 mg per 240 ml) and sits in the moderate range for energy drinks — the same dose as a 473 ml Monster or Rockstar, but noticeably less than Bang or Reign (300 mg) and slightly above a 355 ml Red Bull (114 mg).

To keep within the daily guidance, stick to no more than two cans of Relentless spaced across the day. If you plan to sleep by 23:00, finishing your last can by early afternoon is a safer bet, as the 160 mg dose takes more than 10 hours to drop below 50 mg. Adjust for your own metabolism and sensitivity with our bedtime caffeine calculator.