Testing the Tyrosine/Catecholamine Hypothesis of Oral Contraceptive-Induced Psychological Side-Effects: A Controlled Study on Triphasil®

Abstract

Background: This study was conducted to probe the existence of oral contraceptive (OC)-induced psychological side effects that might be undetectable by psychometric testing. Methods: Triphasil^® was administered during six complete menstrual cycles to young never-OC-users. Plasma Tyr and Trp/Σ-respective competitor neutral amino acids (NAA) ratio and concentrations of other amino acids (AA), known to be involved in the functioning of the central nervous system (CNS) and the synthesis of neurotransmitters, in particular, were used as biochemical markers to assess this likelihood. Factors known to influence plasma AA concentrations such as cortisol and pyridoxal phosphate (PLP, active form of vitamin B₆), both modulators of AA intestinal absorption, were examined. Results: Dietary supply of amino acid substrates (precursors) and blood levels of coenzyme/cofactor (vitamin B₆ and iron) involved were adequate in both groups and were kept constant throughout the treatment. The rise in plasma cortisol, known to be stimulated under the action of estrogen, was significant (p < 0.05) after the first menstrual cycle and remained higher (although not significantly) than mean baseline and reference normal values at the end of the 6-month OC treatment. Plasma Trp/Σ-specific competitor NAA ratio remained unchanged whereas Tyr/Σ-specific competitor NAA ratio was significantly (p < 0.02) reduced after the sixth artificial menstrual cycle. Conclusion: Although plasma AA biochemical markers cannot accurately assess CNS activity, they seem to be more sensitive than a comprehensive psychometric testing (MMPI) in assessing OC-induced psychological changes.