Effect of oral contraceptive consumption timing on substrate metabolism, cognition, and exercise performance in females: a randomised controlled trial

PURPOSE: The pharmacokinetic profile of oral contraceptives (OCs) results in an acute, transient increase in circulating synthetic reproductive hormones. This study aimed to assess the acute effects of OC ingestion on cognitive function, substrate metabolism and exercise performance. METHODS: Sixteen combined OC users ingested either their OC or placebo (PLA) in a randomised, double-blind, crossover manner. After 60 min, participants completed tests of verbal memory and verbal fluency, followed by sub-maximal treadmill exercise for 6 min at 70% lactate threshold (LT) and 90% LT where respiratory exchange ratio (RER), carbohydrate oxidation, fat oxidation, heart rate (HR), rating of perceived exertion (RPE), felt arousal and feeling scale were recorded. Participants then completed an incremental ramp test to exhaustion to assess time to exhaustion (TTE) and peak oxygen uptake (VO2peak), before ingesting the pill corresponding to the opposing condition RESULTS: Compared to PLA, the OC condition has a significantly lower RER, arousal and feeling scale and significantly higher verbal fluency score (all P < 0.05) with no differences in other variables (P > 0.05). CONCLUSION: Combined OC ingestion acutely affects substrate metabolism, affective responses to exercise and verbal fluency. The timing of OC ingestion should be considered in relation to aspects of physiological function.