This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
Worth separating two things that post #57 runs together.
Anticoagulants: no direct interaction with the compounds in this class. Weight loss and body composition changes might affect the clearance or effect of warfarin if you are on it; monitoring INR more frequently during weight loss is reasonable.
It is the sort of thing that seems obvious in retrospect and was not at the time.
On grapefruit, the part that usually goes wrong is that the question is asked as though it has one answer. It has a range, and the width of the range is the interesting bit.
If you can post the two or three numbers you are working from, several people here will check the arithmetic rather than argue about the conclusion.
Source for the grapefruit figure, since it was asked for. It is in the discussion rather than the abstract, which is why the version circulating is stronger than the paper is.
Reading the surrounding paragraph is worth the two minutes. The authors are more careful than their summarisers.
The most defensible general position in this subcategory: identify the plausible mechanism, check whether it has been studied, and where it has not, say that rather than filling the gap.
On post #61 — agreed on the reasoning, with one qualification.
SGLT2 inhibitors: frequently co-administered and relevant to renal and cardiovascular discussion, not to interactions. There is no pharmacokinetic interaction of concern.
A modest claim, modestly supported.
Picking up post #65: that is the part I would want checked first.
I disagree with the framing of grapefruit above, and I think it is a substantive disagreement rather than a terminological one. Setting out why, so it can be checked.
The reasoning depends on an assumption that is doing a lot of work and is never stated. If the assumption holds, the conclusion follows. I do not think it holds generally.
Adding the boring version of grapefruit, because the interesting version keeps getting posted and the boring one is usually right.
Check the ordinary explanations, in order, and stop when one of them accounts for what you are seeing. Most of the time the second one does.
Delayed gastric emptying is the mechanism behind most of the plausible interactions in this class: anything whose absorption depends on how quickly the stomach empties can behave differently.
Building on post #69 rather than restating it.
The most defensible general position in this subcategory: identify the plausible mechanism, check whether it has been studied, and where it has not, say that rather than filling the gap.
Adding the measurement that post #68 says would settle it.
Oral contraceptive absorption has been studied specifically for some compounds in this class and the findings are compound-specific. Generalising from one to another is not supported.
The general answer and the answer for your case may diverge here.
Offering a way to settle grapefruit rather than another opinion about it. Two measurements, taken the same way, a fortnight apart. If the difference is within the noise, the question was not answerable at this precision.
Where a published interaction study exists it usually reports an area-under-curve ratio, and that number is far more informative than a yes-or-no answer.
Agreed, and I will stop repeating the version of this I had been repeating.
Worth stating the null on grapefruit before we explain it: the observation may be nothing. That possibility deserves a sentence and usually does not get one.
A pharmacist can answer most questions in this subcategory in a few minutes with access to a proper interaction database, and that access is the thing a forum does not have.
Where I part company with post #75, and it is a narrow parting.
Insulin and sulfonylureas are the interaction that the labelling in this class flags most explicitly, because the risk is additive glucose lowering. That is a prescribing question and not a forum question.
Adding this to the thread rather than to the wiki, because I am not confident enough for the wiki.
I read the earlier replies on grapefruit twice before writing this, because I had assumed the opposite and wanted to be sure I was disagreeing with what was said rather than what I expected.
A note on how grapefruit gets discussed rather than on grapefruit itself: the confident posts get the replies and the careful ones get ignored, and the careful ones have been right more often.
Where I part company with post #79, and it is a narrow parting.
Anticoagulant questions come up regularly and are the clearest case for professional advice rather than discussion, because the consequence of being wrong is not gradual.
Where I have landed on grapefruit, having got it wrong once in public: the direction is clear, the magnitude is not, and anyone quoting a precise magnitude has borrowed it from somewhere that did not measure it.
Worth separating grapefruit as a question about the compound from grapefruit as a question about the documentation. They get answered by different people and only one of them is answerable here.
Alcohol: no absolute contraindication but it raises gastrointestinal irritation risk and this drug class already does that. The conservative position during titration is to limit it.
Adding a source would improve this post and I do not have one to hand.
Small correction to my own earlier position on grapefruit. I had the units the wrong way round, which changes the conclusion by an order of magnitude and therefore changes it entirely.
The question underneath grapefruit is usually "how would I tell?" rather than "what is true?", and that one has a method attached to it.
Write down what you would expect to see under each hypothesis before you collect anything. If they predict the same observation, collecting it will not help.
A supplement is a drug for interaction purposes, and the fact that it is sold without a prescription tells you nothing about whether it interacts. The paperwork is usually worse rather than better.
It is a small point and it changes the answer, which is an awkward combination.