Heart palpitations can show up around 100–200 mg in some people, and the risk rises as daily intake pushes past 400 mg.

Most healthy adults can keep caffeine near 400 mg a day, while staying under 200 mg in one sitting to protect sleep and comfort.

There’s no single caffeine number that guarantees a heart attack; risk climbs with high doses taken fast, especially from concentrated products.

Most pregnancy guidance caps caffeine at 200 mg a day; going above that, day after day, is tied to a higher miscarriage risk in studies.

For healthy adults, 400 mg of caffeine per day is the upper intake many health agencies cite as safe.

Most pregnancy guidelines cap caffeine at 200 mg a day, which is roughly one 12-oz brewed coffee.

Many clinicians advise zero caffeine under age 12; for teens, a common ceiling is 100 mg per day, with weight-based limits near 2.5–3 mg/kg.

Most healthy adults do best at 400 mg of caffeine a day or less, with lower limits during pregnancy and for people who feel it sooner.

A typical 8-ounce cup of black tea lands around 40–70 mg of caffeine, with the final amount driven by leaf dose, brew time, and water heat.

Most breastfeeding moms can keep caffeine at 200–300 mg a day without issues for many babies, with lower targets for newborns.