These sites could be helpful for those who take supplements or may take supplements.
nlm.nih.gov/medlineplus/dru...
As well as this one:
Browse dietary supplements and herbal remedies to learn about their effectiveness, usual dosage, and drug interactions.
I've actually found the Mayo Clinic website to be the best one. It gives not only background, drug interactions, contraindications but also doing suggestions AND dosing examples which is often missed by other websites.
For example the attached dosing for COq10 gives more than 50 examples of different things COQ10 has been used for, dosing ranges and length of time studies.
I've not found any website that does better in this regard.
mayoclinic.org/drugs-supple...
Unfortunately finding unbiased plain English discussions of the efficacy of some supplements can be very difficult.
Apixaban and Supplements. 
Magnesium supplements 
Magnesium supplements 
BioCare Supplements
