Vitamin K1 and Testosterone: No Interaction
Vitamin K1 (phytonadione) can be safely taken together with testosterone therapy without any special precautions or clinically significant drug interactions.
No Evidence of Drug Interaction
The available evidence shows no documented interaction between vitamin K1 and testosterone:
FDA drug labeling for phytonadione lists only anticoagulants (warfarin, coumarin derivatives) as having drug interactions, with no mention of testosterone or other hormonal therapies 1
Endocrine Society testosterone guidelines do not identify vitamin K as a contraindication, precaution, or monitoring consideration when prescribing testosterone therapy 2
AUA erectile dysfunction guidelines discussing testosterone therapy make no reference to vitamin K interactions or precautions 3
The only documented drug interaction for vitamin K1 is with anticoagulants (warfarin, coumarin derivatives), where vitamin K1 can reverse their anticoagulant effects by promoting synthesis of vitamin K-dependent clotting factors 1.
Physiologic Considerations
While recent research suggests MK-4 (menaquinone-4, a vitamin K2 homolog) may enhance testosterone production in animal models 4, this represents a potential synergistic effect rather than an adverse interaction. Vitamin K1 (phytonadione) did not demonstrate this effect 4.
Clinical Bottom Line
Patients on testosterone therapy can take vitamin K1 supplements without dose adjustments, special monitoring, or timing considerations. The two medications work through completely independent mechanisms:
- Testosterone: Acts on androgen receptors to produce androgenic and anabolic effects
- Vitamin K1: Serves as cofactor for γ-glutamylcarboxylase in synthesis of clotting factors and bone proteins 5
The only scenario requiring caution is if the patient is also taking warfarin or other vitamin K antagonist anticoagulants, in which case vitamin K1 intake must be monitored and kept consistent to maintain stable anticoagulation 5.