Six studies report that a one-time dose of caffeine (200-300 mg) raises blood pressure, by 3 to 12 mmHg in systolic blood pressure and 3 to 4 mmHg in diastolic blood pressure.  Two studies report that the effect of habitual consumption of caffeine on blood pressure is unclear. 

• Grade I means there is Good/Strong evidence supporting the statement;
• Grade II is Fair;
• Grade III is Limited/Weak;
• Grade IV is Expert Opinion Only;
• Grade V is Not Assignable.
• High (A) means we are very confident that the true effect lies close to that of the estimate of the effect;
• Moderate (B) means we are moderately confident in the effect estimate;
• Low (C) means our confidence in the effect estimate is limited;
• Very Low (D) means we have very little confidence in the effect estimate.
• Ungraded means a grade is not assignable.