There is a general concern about Bioperine... the pepper extract in some of Doctor's Best products that is there for enhancing absorption. The RX drugs we take are designed in doses to be absorbed WITHOUT enhancements. This is similar to the effects of grapefruit juice on many drugs. It is the same issue. The Bioperine may push more of the drug thru the membranes of the GI tract, leading to overdose situations or increased side effects.

I have seen reports that one needs up to 20mg of Bioperine to affect the RX drugs that people take. But I don't think that amount is proven yet. Tests have not been done on every drug.
But since amitriptyline and methadone are on the lists for potential problems with heart QT prolongation, I'd avoid the products that contain Bioperine.

So because you are on Methadone and amitriptyline, it would be a good idea to get a magnesium product that does not have the Bioperine in it, just to be safe.