Posting this under the heading it deserves: Grapefruit: why this class is not the class that cares Everything below is what sits behind that.
I was wrong about Grapefruit in a thread last spring and I would like to correct it publicly rather than quietly.
The error was in the units, which changed the conclusion by an order of magnitude. Setting out the corrected version, and the way I now check for that class of mistake.
Small methodological point on Grapefruit: repeating a measurement is cheap and resolves most of what is being argued about here at no cost to anyone.
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.
On balance I think that is right, and I would not bet much on it.
I read post #2 twice before replying, because I had assumed the opposite.
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.
I would treat that as a working assumption and revisit 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.
I have written this out at length because the short version keeps being misread.
Post #4 is right about the mechanism and I think understates the practical bit.
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.
Noting that the question and the thing people usually mean by it are different.
Coming back to post #7, because the follow-up matters more than the original answer.
Careful with the language on Grapefruit. "Not detected" and "not present" are different findings and the first is a statement about the method.
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.
That is the shape of it. The detail is where I would expect to be corrected.
Post #9 answers the question as asked. The question underneath it is different.
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.
One case, stated as one case.
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.
I keep a log of this specifically because memory is unreliable about it.
Marking my place. If it changes for me I will come back and say so.
Coming back to post #13, because the follow-up matters more than the original answer.
SGLT2 inhibitors: frequently co-administered and relevant to renal and cardiovascular discussion, not to interactions. There is no pharmacokinetic interaction of concern.
Anyone with a larger sample, please post it.
Post #13 is right about the mechanism and I think understates the practical bit.
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.
I have seen it go both ways, which is why I hedge.
The arithmetic on Grapefruit is the easy part and it is where the errors are, which is an uncomfortable combination. Show your working and someone will catch it.
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.
I am reporting what happened, not recommending it.
The honest answer on Grapefruit is that it depends, and the useful part is the list of what it depends on. Four items, in rough order of how much they matter.
Most people get the first two right and then argue about the fourth.
On Grapefruit the community has more anecdote than the confidence in this thread implies, and I include my own contribution in that.
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.
Building on post #22 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.
I looked this up rather than remembered it, which is the right order.
Useful. I have added it to my own notes with the date on it.
Posting my Grapefruit numbers with the method attached so they can be discounted properly. Uncontrolled, unblinded, and collected by someone who wanted a particular answer.
I read post #25 twice before replying, because I had assumed the opposite.
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.
If the premise is wrong, everything after it is decoration.
The practical version of Grapefruit is three sentences long. The rigorous version is three pages and reaches the same conclusion with the conditions attached.
Adding the measurement that post #26 says would settle it.
SGLT2 inhibitors: frequently co-administered and relevant to renal and cardiovascular discussion, not to interactions. There is no pharmacokinetic interaction of concern.
For what it is worth, the same held on the two occasions I checked.
Post #28 describes the usual case. This is about the unusual one.
Trying to state the Grapefruit position in a way that someone who disagrees would recognise as fair, because I do not think the version in this thread passes that test.