Is there an interaction between oral contraceptives (Cilest) and Red Bull?/nA woman using oral cont

Fråga: Is there an interaction between oral contraceptives (Cilest) and Red Bull? A woman using oral contraceptives containing ethinylestradiol and norgestimate (Cilest) suffers from intermenstrual bleeding. She drinks one can of Red Bull every day. The gynaecologist has found no reason for these bleedings.

Sammanfattning: We have found no data supporting an interaction as the cause of intermenstrual bleeding. Oral contraceptives can decrease the clearance of caffine. The natural formation and/or the excretion of taurine may be decreased by oral contraceptives. No interaction between the other ingredients and oral contraceptives has been found but can not be excluded due to lack of documentation.

Svar: Red Bull is marketed as an energy enhancing beverage. One can (250 mL) of Red Bull contains taurine 1000 mg, glucurolactone 600 mg, caffeine 80 mg, vitamin B6, vitamin B12, sacarose, glucose. The diet variant contains acesulfam K, aspartam and sucralose instead of sacarose and glucose (1).

We have found no published data indicating that any of the ingredients in Red Bull should affect the pharmacokinetics of oral contraceptives.

It is well known that oral contraceptives inhibits the metabolism of caffeine and increases its half-life by approximately 50%. This is probably due to CYP1A2 inhibition by estrogens (2).

Taurine is an aminoacid naturally occurring in the body. Taurine is produced naturally in the body via metabolism of methionine and cysteine. It is found in almost all tissues and a 60 kg person has in average 60 g taurine in the body. Taurine is mainly excreted in the urine but can also be found in bile and faeces (3). One study have investigated the urinary excretion of taurine in women in the post-partum period, during lactation and when using oral contraceptives. The excretion of taurine was 196 mg/d (115-331) in a control group consisting of 20 women, and 12 mg/d in four women using oral contraceptives. The excretion was low in the post-partum period but increased markedly during lactation (4). The women in this study were using high dosed oral contraceptives.

The overall toxicity of taurine seems to be low although there is no safety data for intake of daily doses above 400 mg/d (5). One case of encephalopathy have been reported in a bodybuilder who had ingested 14000 mg of taurine in combination with insulin seven days prior to admission (6).

An in vitro study of the effect of taurine on coagulation has been found. Taurine at different concentrations was added to donor blood and prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT) and platelet aggregation was measured. TT was increased by 9% wich was stastistically significant although considered as clinically insignificant. Taurine decreased thrombin induced platelet aggregation by 10%. The clinical importance of this finding is probably low (7).

We have found no data of an interaction between oral contraceptives and the other ingredients nor any reports of hemorrhage or effect on blood coagulation.

It can be noted that intermenstrual bleeding is reported as a common adverse effect during treatment with Cilest (8).