If anyone here decides to use a mixed supplement that contains
methylcobalamin, you need to take it on an empty stomach.

Most commercial supplements are not labeled correctly in this regard.

Overall Patrick is correct, as we have many posts here in the past where combined products have been discussed. He put his post together very well, summarizing the topic.

Another feature is to avoid mixtures with "proprietary" listings on the label....these are long lists of important sounding ingredients but they do not have actual milligram details for each. This is a trick, to get you to buy....as the mixture may only have 1mg of one item and many milligrams of another. It is really a bad way to start using any supplement. Also avoid websites that are "too slick" and make you hunt and search to find the ingredients. Sometimes they even automatically bill your charge card, without your permission. There are many scams out there, and you can Google a place before buying to see if complaints are logged on consumer sites.

It is ideal to get some testing, at least for B12 and Vit D, before starting supplements. This way you can pick doses unique to your problem.

The only "mixture" I take is B-right by Jarrow, all others are single dose.

Keep in mind that nutrients sometimes reach a plateau...the enzyme systems that use them can become saturated, and overtime you may be able to use less to maintain.
Staying at very high doses over a long period of time may lead to a vitamin "dependency" ...meaning your body will shift and maybe require those high doses. This happened with Vit C megadosing in the past..Where lowering the dose revealed a strange sort of scurvy in those people.

If you are very deficient, it may take a while to see results with some nutrients, as the body has to "wake up" and set certain metabolic systems and enzymes going again, after a period of
"drought" . The body is not a static machine... it is always changing and adjusting.