Genesight and similar technologies are bleeding edge and not fully proven.
That's not quite true.
Which enzymes are coupled to which drugs is a known thing; no guesswork there.
If an enzyme is not present in the individual, or severely mutated, and it happens to be required in order to process Drug A - then there's a good chance the individual will not process Drug A as it is intended to work in the standard population.
The problem is, they don't have the full picture on how slight variations in the enzymes may effect things; they also have not fully catalogued how some mutations or deficiencies get made up for with other unique enzyme combinations. And of course, the majority of detailed research on a drug is connected to the original source - so, the brand formulation. In drugs that have been around so long, the generic is well-understood (very few meds), it's a bit more straightforward. But if a drug has only recently been released a generic, and has an especially unique action...the makers of that generic drug are not going to be creating an identical formulation. It's got to have bioavailability inside certain parameters...sometimes less, sometimes more than the brand drug. And that affects how the drug hits the individual, obviously.
So: the big basics of genetic testing are pretty solid, but those are simple, simple things. Like the e-z big-note piano music that you give to a 6 year old studying piano. They can play a song, and you will understand it's the Ode To Joy from Beethoven's fifth symphony - but it bears little resemblance to a world class orchestra plus chorus playing the exact same tune.
I'm a rapid metabolizer, and having it confirmed was reassuring for me. I already knew it was probably the answer to why very few drugs work for me, and why I have to take them at exceedingly high doses. But knowing there was some science to actually back that up, helped fill in some gaps.
For poor metabolizers, they do know enough to give you an understanding of what will likely make you feel quite ill; you can avoid those. You can also discover good reasons to start at what might be considered a sub-therapeutic dose, only it's quite enough for the poor metabolizer.
The test is useful just to give you a sense of:
- What to avoid
- Whether anything will work at all
- If you will respond better to lower or higher doses.
It's also very important to get it done with doctors who are experienced in interpreting the results. In the US, that's generally university hospitals and teaching hospitals.