Most articles about keto talk about what to eat. This one is about something that matters more if it applies to you: what is already in your bathroom cabinet. A ketogenic diet is not a gentle tweak. It changes your blood sugar, your blood pressure, your fluid balance and your metabolism, sometimes within days, and if you take medication for any of those things, the dose that was right for your old way of eating can quickly become too much. This is the one area of keto where the honest advice is not “give it a go and see”, but “talk to your doctor or pharmacist before you start”. Here is why, and what to watch.
To be clear from the outset, this is general information to help you have a better-informed conversation with a professional. It is not medical advice, it does not tell you how to change any dose, and you should never stop or alter a prescribed medication on your own. With that said, the detail below is the kind of thing that is genuinely useful to walk into that appointment already understanding.
The core idea: the diet changes the illness, so the dose has to keep up
Keto does not interact with most drugs the way grapefruit juice famously does, by directly interfering with how the body processes them. It does something more fundamental: it improves, quite quickly, several of the conditions those drugs are prescribed to manage. That sounds entirely good, and mostly it is, but it creates a specific hazard. If a medication is lowering your blood sugar or your blood pressure, and the diet is now also lowering your blood sugar or blood pressure, the two can stack up and push you too far. The result can be a hypo, a faint, or in one particular case a dangerous metabolic emergency. The danger is not the diet or the drug alone; it is the drug being dosed for a body that has suddenly changed.
This is why timing matters so much. Blood sugar can drop on the very first day of low-carb eating, which is why some medications need adjusting immediately rather than later. Knowing which ones, and in which direction, is the whole game.
Diabetes medications: the most urgent group
If you have type 2 diabetes and take medication for it, this is the part to read twice, because the changes can be rapid and some of the drugs carry real risk on a low-carb diet. A 2021 review in Frontiers in Nutrition, written specifically to help clinicians adapt diabetes medication to low-carbohydrate eating, sets out just how fast and how significant these adjustments can be.
Insulin. Carbohydrate is the main thing that raises blood sugar, so cutting it sharply means you need much less insulin to cope, often dramatically less. The review notes that insulin doses are commonly halved on the very day the diet starts, and sometimes reduced much further after that, precisely because leaving the old dose in place can cause hypoglycaemia. If you inject insulin, starting keto without a plan to reduce it is genuinely risky, and this must be managed with your diabetes team.
Sulfonylureas and meglitinides. These are the tablets, with names like gliclazide and glipizide, that push your pancreas to release insulin whether or not you have eaten carbohydrate. On a low-carb diet that becomes a recipe for hypos, because they keep driving insulin down while your carbs are already low. Clinicians who use low-carb diets routinely halve or stop these drugs at the start for exactly this reason. One study found that around 90 per cent of patients came off sulfonylureas when they adopted a very-low-carbohydrate diet.
SGLT2 inhibitors: the serious one. This class, the so-called gliflozins, includes drugs like empagliflozin, dapagliflozin and canagliflozin. Combining them with a ketogenic or very-low-carbohydrate diet markedly raises the risk of a condition called euglycemic diabetic ketoacidosis. Ordinary diabetic ketoacidosis usually comes with sky-high blood sugar that rings alarm bells; the euglycemic version produces the same dangerous acid build-up while blood sugar stays near normal, which means it is easily missed until the person is very unwell. A 2021 case series in AACE Clinical Case Reports documented exactly this happening to people on these drugs who started a ketogenic diet, and noted that more than 2,500 cases of SGLT2-related ketoacidosis had been reported to the United States drug-safety system. Doctors experienced with keto routinely stop these drugs before a patient begins. If you take a gliflozin, the message is simple and strong: do not start keto without medical guidance, and learn the warning signs, which include nausea, vomiting, abdominal pain, rapid breathing and feeling profoundly unwell, even if your glucose meter looks fine. Those symptoms warrant urgent medical attention.
Metformin. The good news in the group. Metformin does not generally cause hypos on its own, so it is usually considered lower risk and is often continued, but it should still be part of the conversation with your doctor rather than assumed safe.
The overall pattern, drawn from the clinical guidance, is that insulin, sulfonylureas and SGLT2 inhibitors are the medications most likely to need prompt adjustment or stopping, and that the first few weeks call for close blood-sugar monitoring and easy contact with whoever manages your diabetes.
Blood pressure medications and diuretics
The second group to watch treats high blood pressure. Two things happen on keto that affect them. First, in the early days the body sheds sodium and water, an effect a bit like taking a mild diuretic, which can lower blood pressure quickly. Second, over the following weeks and months, the weight loss keto tends to produce lowers blood pressure more gradually. Stack either of these on top of blood-pressure medication and you can end up with blood pressure that falls too far, leaving you dizzy, lightheaded or prone to fainting when you stand.
The timing here is gentler than with diabetes drugs. As the deprescribing guidance notes, blood pressure usually changes more slowly than blood sugar, over weeks to months rather than on day one, so there is less need to pre-emptively cut the dose and more need to monitor and adjust as you go. Diuretics deserve particular care, because the diet is already increasing your fluid and salt loss, and adding a diuretic on top can compound dehydration and throw your electrolytes off. This connects directly to the standard keto advice to keep your salt and minerals up, covered in the guide on electrolytes, and to the honest picture of how keto affects blood pressure in the first place. The practical point is to monitor your blood pressure at home and keep your doctor informed, so the medication can be reduced in step with the improvement rather than lagging behind it.
Other interactions worth flagging to a pharmacist
Beyond the two big groups, a 2025 review in Annals of Medicine on the contraindications and drug interactions of the ketogenic diet lists several other situations worth knowing about. None of these should put you off, but each is a reason to have your full medication list checked.
A few stand out. People who take certain anti-seizure medications, particularly the ones that already acidify the body such as topiramate and zonisamide, may face a higher risk of side effects like kidney stones and excess acidity when these are combined with a ketogenic diet, which itself shifts acid balance. Anyone on lithium should be cautious, because keto’s effects on sodium and fluid can alter lithium levels, and lithium has a narrow safe range. Those on warfarin may find their blood-thinning control shifts as their diet changes, so their monitoring may need to be tightened for a while. And some medications, such as steroids, can work against ketosis itself. This is not an exhaustive list, and that is rather the point: the diet can subtly change how various drugs are absorbed, processed and cleared, which is precisely the kind of thing a pharmacist is trained to catch.
Why the pharmacist is your quiet ally here
It is worth singling out pharmacists, because they are the most accessible and often the most overlooked help for this. They hold your complete medication list, they understand interactions in detail, and you can usually speak to one without an appointment or a wait. Before you start keto, a short conversation with your pharmacist about your full list, prescription and over-the-counter, is one of the easiest safety steps you can take, and it costs nothing.
A safe way to start if you take any of this
If none of the above applies to you, you can largely disregard it and start keto as any healthy adult would. If any of it does apply, here is the sensible sequence. Write down every medication and supplement you take. Before changing your diet, speak to your GP, diabetes team or pharmacist and ask specifically about insulin, sulfonylureas, SGLT2 inhibitors, blood-pressure tablets and diuretics. If you take insulin, a sulfonylurea or an SGLT2 inhibitor, treat medical supervision as non-negotiable rather than optional. Agree a monitoring plan, which for most people means checking blood sugar and blood pressure at home, especially in the first few weeks when things change fastest. And learn the red-flag symptoms for your situation: the shakiness, sweating and confusion of a hypo, the dizziness of blood pressure dropping too low, and, for anyone on a gliflozin, the signs of ketoacidosis even when glucose is normal.
The reassuring part
It would be easy to read all this as a warning against keto, and it is not. Look again at why these adjustments are needed: they are needed because the diet is improving the very conditions the drugs were treating. Blood sugar falling so far that insulin must be cut is, in itself, good news. Blood pressure dropping enough to reduce a tablet is the outcome people on those tablets are hoping for. Under proper supervision, many people on a low-carb diet end up needing less medication, not more, and for some that is one of the main reasons they do it. The hazard is purely one of timing and coordination, the diet racing ahead of a dose that has not yet caught up. Manage that with your clinician and the risk is well controlled.
The bottom line
A ketogenic diet can change how your medications affect you, quickly and significantly, because it improves the conditions many of them treat. The drugs that need the most attention are insulin and sulfonylureas, which can cause hypos as your blood sugar falls, and SGLT2 inhibitors, which carry a real risk of euglycemic ketoacidosis on keto and are usually stopped beforehand. Blood-pressure medication and diuretics need monitoring and likely reduction as your readings improve, and a handful of other drugs are worth a pharmacist’s eye. If you take any of these, the rule is the same and it is not negotiable: talk to a professional before you start, agree how you will monitor and adjust, and never change a dose yourself. Do that, and what looks like a list of dangers becomes what it really is, a set of good-news adjustments to manage carefully.
This is general information, not medical advice, and it is not a guide to changing any medication. Do not start, stop, or alter any prescribed drug without your doctor or pharmacist. If you take insulin, a sulfonylurea, an SGLT2 inhibitor, blood-pressure medication or a diuretic, seek professional advice before beginning a ketogenic diet, and seek urgent care for symptoms of low blood sugar, very low blood pressure, or ketoacidosis (including nausea, vomiting, abdominal pain or breathlessness even with normal blood sugar).
Sources: Adapting Medication for Type 2 Diabetes to a Low Carbohydrate Diet. Frontiers in Nutrition. 2021. Read it here. Euglycemic Diabetic Ketoacidosis Caused by SGLT2 Inhibitors and a Ketogenic Diet: A Case Series and Review of Literature. AACE Clinical Case Reports. 2021. Read it here. The ketogenic diet is not for everyone: contraindications, side effects, and drug interactions. Annals of Medicine. 2025. Read it here.