Impaired elimination of caffeine by oral contraceptive steroids.
Level 3 - non-randomized controlled study
Non-randomized prospective controlled pharmacokinetic comparison study
What was done
A single oral dose of 250 mg caffeine was administered to 31 healthy participants: 13 males, 9 females not taking oral contraceptive steroids (OCS), and 9 females taking OCS. Pharmacokinetic parameters, including elimination half-life, total and free plasma clearance, volume of distribution, and plasma protein binding, were measured and compared across groups.
What was found
Women taking OCS had a significantly longer caffeine elimination half-life than women not taking OCS (10.7 ± 3.0 hr vs. 6.2 ± 1.6 hr, p < 0.001). Total plasma clearance (0.79 ± 0.21 ml/min/kg vs. 1.3 ± 0.35 ml/min/kg) and free clearance (1.12 ± 0.28 ml/min/kg vs. 1.97 ± 0.57 ml/min/kg) were significantly lower in OCS users. Volumes of distribution and plasma binding were similar between female groups. Non-OCS women had pharmacokinetic values similar to men, except for a significantly larger volume of distribution (p < 0.05).
Why it matters
This study demonstrates that oral contraceptive steroids impair caffeine clearance and nearly double its elimination half-life.
Limits
The sample size is small (31 participants total, with only 9 per female group). The abstract does not specify oral contraceptive formulations, doses, or menstrual cycle phases, and clinical adverse effects of prolonged caffeine exposure were not evaluated.
Cited by
- context The elimination half-life of caffeine is between 6 and 8 hours.