A single 15-ounce can of Starbucks Doubleshot Energy contains about 135 mg of caffeine, which is well within the FDA’s 400 mg daily limit for healthy adults. On caffeine alone, one can isn’t dangerous. But caffeine is only part of the picture. The drink also packs sugar, taurine, guarana, and ginseng, and the combination of these ingredients creates cardiovascular effects worth understanding before you make it a daily habit.
What’s Actually in the Can
The 135 mg of caffeine in a Starbucks Doubleshot Energy is roughly equivalent to a medium cup of brewed coffee. That puts it in the moderate range for energy drinks. A standard 8.4-ounce Red Bull has about 80 mg, while larger Monster cans can reach 160 mg or more. So the Doubleshot isn’t extreme, but it’s not light either.
Beyond caffeine, each can contains 1,800 mg of taurine (an amino acid), 120 mg of ginseng extract, and 90 mg of guarana extract. Guarana is a plant-based caffeine source, which means the total stimulant load is slightly higher than the 135 mg listed on the label. The guarana adds roughly 30 to 40 mg of additional caffeine equivalent, pushing the true stimulant content closer to 170 mg per can. The drink also contains added sugar, typically around 26 grams per can, which is about six and a half teaspoons.
How It Affects Your Heart and Blood Pressure
The real concern with energy drinks isn’t any single ingredient. It’s how caffeine, taurine, and sugar interact inside your cardiovascular system. Research published in the World Journal of Cardiology found that a single 355 mL energy drink raised systolic blood pressure by about 10 mmHg, diastolic pressure by about 7 mmHg, and heart rate by 20 beats per minute in healthy young adults. A separate study of 50 young, healthy subjects found systolic blood pressure climbed from 112 to 121 mmHg within two hours of drinking one can.
These aren’t catastrophic changes for someone with normal blood pressure. But they add up. One study of fifteen healthy adults found that the cardiovascular effects were actually greater after five consecutive days of consumption than after just the first day. Your body doesn’t fully adapt to the daily spike. It compounds. Researchers also observed increases in cerebrovascular resistance (meaning blood vessels in the brain tighten) and decreases in cerebral blood flow velocity, which is the speed at which blood moves through your brain.
The most serious adverse events tied to energy drinks in medical case reports include arrhythmias (irregular heartbeats, accounting for 35% of cardiac-related reports), coronary vasospasm, and dangerously elevated blood pressure. These events are rare and typically involve people who consumed multiple energy drinks in a short window, combined them with alcohol or stimulant medications, or had an undiagnosed heart condition. But they illustrate that the caffeine-taurine combination can increase platelet clumping and disrupt normal blood vessel function in susceptible people.
The Sugar Factor
At roughly 26 grams of sugar per can, a daily Doubleshot Energy habit adds about 180 empty calories and over 180 grams of sugar to your weekly intake. The American Heart Association recommends no more than 36 grams of added sugar per day for men and 25 grams for women. One can nearly maxes out the entire daily allowance for women and takes a significant chunk for men, leaving almost no room for sugar from any other source that day.
Over time, consistent high sugar intake is linked to weight gain, insulin resistance, and increased risk of type 2 diabetes. The rapid blood sugar spike from a sugary energy drink followed by a crash can also leave you more fatigued than before you drank it, which creates a cycle of reaching for another one.
One Can vs. a Daily Habit
An occasional Starbucks Doubleshot Energy isn’t likely to cause harm for a healthy adult. The caffeine is moderate, and a single exposure to the taurine and guarana blend won’t produce lasting effects. The problems start when “occasional” becomes “every morning” or when one can becomes two.
Two cans in a day pushes your caffeine intake to roughly 340 mg from this drink alone, before counting any coffee, tea, or chocolate you consume. Add a morning coffee and you’re brushing up against or exceeding the 400 mg FDA threshold. At that level, you’re more likely to experience jitteriness, disrupted sleep, increased anxiety, and the blood pressure effects documented in the research.
If you have high blood pressure, a heart condition, anxiety disorder, or sensitivity to caffeine, the risk profile shifts significantly. The 10 mmHg systolic blood pressure increase that’s a temporary nuisance for a healthy 25-year-old becomes a genuine concern for someone already managing hypertension. Pregnant individuals should also be cautious, as caffeine recommendations during pregnancy are typically capped at 200 mg per day, and the added guarana makes it easy to overshoot that number.
Healthier Ways to Get the Same Boost
If you’re drinking Doubleshot Energy for the caffeine, a plain brewed coffee delivers a similar amount without the sugar, taurine, or guarana. Black coffee has essentially zero calories. If you prefer cold and convenient, cold brew concentrate diluted with milk provides comparable caffeine in a format that’s just as portable.
If the sugar and flavor are part of the appeal, switching to the sugar-free version of the drink (where available) eliminates the biggest daily health cost. You’ll still get the caffeine and supplemental ingredients, but without the 26 grams of added sugar driving your blood glucose up and down throughout the afternoon.
For sustained energy without stimulants, consistent sleep, hydration, and balanced meals do more than any can. That sounds generic, but the afternoon energy crash that sends most people to the vending machine is typically caused by a combination of mild dehydration and a blood sugar dip after lunch. Drinking water and eating a protein-rich snack often resolves the same fatigue that an energy drink temporarily masks.