Japanese Mister Donut Serves Highest Caffeine Black Coffee in Taoyuan Test

If you drink multiple cups of black coffee a day, you might be getting more caffeine than you think—potentially enough to cause jitters, insomnia, or worse. In May, Taoyuan County’s health authorities tested 32 black coffee samples from local chains to find out just how much caffeine is really in your cup.

The highest caffeine level came from Japan’s Mister Donut, at 166mg per 240cc cup—nearly triple Starbucks’ lowest result of 53mg. Health officials recommend no more than 300mg of caffeine daily (about two to three cups) to avoid health risks.

How the Test Was Conducted

Taoyuan County’s Health Bureau inspected 15 chains across three categories: Western fast food (like Mister Donut), convenience stores, and dedicated coffee shops. Each sample was a standard 240cc cup of unsweetened, uncreamed black coffee. Results were analyzed for caffeine content per serving.

Caffeine Levels by Chain Type

The average caffeine content varied significantly by store type: Western fast food averaged 101mg per cup, convenience stores 115mg, and specialty coffee shops 110mg. The full breakdown showed wide variation, with Mister Donut’s 166mg far exceeding others, while Starbucks came in at the low end with 53mg.

Why Caffeine Limits Matter

According to EU food safety experts, adults should limit daily caffeine intake to 300mg—about two to three average cups of black coffee. Exceeding this can lead to side effects like heart palpitations, anxiety, insomnia, headaches, stomach pain, flushing, nausea, frequent urination, and muscle tremors. Long-term overconsumption may also cause dependency, with withdrawal symptoms including headaches, fatigue, irritability, nausea, and intense coffee cravings. Vulnerable groups—including pregnant women, those with heart conditions, anxiety disorders, or stomach issues—face additional risks such as fetal abnormalities, heart arrhythmias, panic attacks, or worsened ulcers.

Frequently Asked Questions

Which chain had the highest caffeine content in the Taoyuan test?

Japan’s Mister Donut had the highest caffeine level at 166mg per 240cc cup of black coffee, nearly three times higher than some other tested brands.

Which chain had the lowest caffeine content?

Starbucks had the lowest caffeine level in the test, at 53mg per 240cc cup of black coffee.

What is the safe daily caffeine limit for adults?

Health authorities recommend adults consume no more than 300mg of caffeine per day—that’s roughly two to three average cups of black coffee—to avoid negative health effects.

What are the risks of too much caffeine?

Excessive caffeine can cause heart palpitations, anxiety, insomnia, headaches, stomach pain, flushing, nausea, frequent urination, and muscle tremors. Long-term overuse may lead to dependency and withdrawal symptoms, and increase health risks for pregnant women, heart patients, and those with anxiety or stomach conditions.

How was the caffeine in these coffees measured?

Taoyuan health officials tested 32 samples from 15 chains, using a standard 240cc serving size for each unsweetened, uncreamed black coffee to ensure consistent comparison.

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