Each day about 75 percent of Americans consume coffee, which contains the world's most popular stimulant -- caffeine -- reports Rice University. Although caffeine is generally considered safe, certain people, such as pregnant women or people on certain medications, may need to monitor their intake. Not all coffee is created equal when it comes to caffeine content. A coffeehouse brew can contain as much as double what you'll find in a homemade cup of instant, while fancy coffee drinks also range wildly in content.
What Caffeine Does
Caffeine suppresses a compound in the brain called adenosine, which is responsible for keeping dopamine and norepinephrine in check. Basically, caffeine allows these excitatory neurotransmitters free reign to keep you alert and energized. In first-time uses, caffeine can increase blood pressure and pulse -- but with regular use you can become desensitized to these effects and somewhat addicted to the substance. Caffeine naturally occurs in coffee, and you can get a safe dosage in about two to four cups, notes CNN. Caffeine pills may contain about the same amount as a cup of coffee, but it's much easier to overdose when swallowing small capsules.
Your Average Cup
A 12-ounce cup of coffee that you brew at home contains about 100 to 160 milligrams of caffeine. Use a coffee maker with coffee pods and you're likely to get between 75 and 150 milligrams per cup. Instant coffee contains between 135 and 148 milligrams per cup. Purchase that cup at a coffeehouse and you'll get between 178 and 260 milligrams in a 12-ounce serving.
A shot of espresso contains about 150 milligrams of caffeine. Any specialty drink, such as a mocha or latte, made with a single shot will thus also contain 150 milligrams. Frozen coffee drinks also contain significant amounts of caffeine -- between 140 and 260 milligrams per serving.