Interactions
Hair loss medication interactions
Plain-English clinical answers to the most common drug-drug and drug-test interactions involving hair loss medication and the supplements we range. BNF and UK Summary of Product Characteristics sources cited on every page.
Interactions covered
CAUTION
Finasteride 1 mg and PSA (prostate-specific antigen) test
CAUTION: finasteride approximately halves measured serum PSA at the licensed 1 mg dose, so any PSA value taken during finasteride therapy must be DOUBLED for in...
Read full answer →AVOID
D-Biotin (Vitamin B7) and Thyroid function tests (TSH, free T4, free T3)
AVOID taking high-dose biotin within at least 48 to 72 hours of a thyroid function test (TSH, free T4, free T3) because biotin can produce falsely high or false...
Read full answer →CAUTION
Iron with Vitamin C (or any iron salt) and Levothyroxine
CAUTION: oral iron reduces levothyroxine absorption. Separate doses by at least 2 hours (UK SmPC); NICE and BNF guidance commonly advises at least 4 hours....
Read full answer →AVOID
Vitamin K2 (MK-7) and Warfarin (and other coumarin anticoagulants)
AVOID starting Vitamin K2 supplementation without specialist review if you are on warfarin or another coumarin anticoagulant. Vitamin K antagonises the mechanis...
Read full answer →ASK PRESCRIBER
Finasteride 1 mg and Testosterone replacement therapy (Testogel, Tostran, Testavan)
ASK PRESCRIBER: combining finasteride with testosterone replacement therapy (TRT) is a deliberate clinical strategy in some hair-loss cases on TRT, because TRT ...
Read full answer →ASK PRESCRIBER
Oral minoxidil (low dose) and Blood pressure medicines (and other medicines that lower blood pressure)
ASK PRESCRIBER: oral minoxidil lowers blood pressure, and the Loniten SmPC states that 'the effect of minoxidil may be additive to concurrent antihypertensive a...
Read full answer →CAUTION
Oral minoxidil (low dose) and Sildenafil and other PDE5 inhibitors (tadalafil, vardenafil, avanafil)
CAUTION: neither the Loniten nor the Viagra SmPC names this pair, but the BNF lists minoxidil with sildenafil, tadalafil, vardenafil and avanafil as combination...
Read full answer →CAUTION
Dutasteride 0.5 mg and CYP3A4 inhibitors (some antifungals, antibiotics, HIV medicines, verapamil, diltiazem)
CAUTION: the Avodart SmPC warns that long-term use of dutasteride with potent CYP3A4 inhibitors 'may increase serum concentrations of dutasteride', and that ver...
Read full answer →ASK PRESCRIBER
Saw palmetto (Serenoa repens) and Finasteride 1 mg
ASK PRESCRIBER: no formal interaction between saw palmetto and finasteride is listed in the Propecia SmPC, but saw palmetto is thought to act on the same hormon...
Read full answer →Every MHRA Drug Safety Update affecting these medicines, in date order →