You take something every morning. Maybe it is for blood pressure, or your thyroid, or your mood, or your blood sugar. And now you want to try a dry fast, and nobody has told you the one thing you actually need to know first: do you keep taking it, or do you stop?
That question matters more than almost anything else about your fast, because there are two ways to get hurt and they point in opposite directions. One person keeps taking a drug that becomes dangerous the moment they stop drinking water, and ends up in real trouble. Another person, trying to be safe, stops a medication cold, and the stopping is what harms them, sometimes far worse than the drug ever could. Both of them thought they were being careful.
I want to give you the honest map, because most fasting advice online either ignores medications entirely or waves its hands and says "talk to your doctor" without telling you what to actually ask. You should talk to your doctor. This article is about walking in already knowing which of your medications are the ones that matter, so that conversation is five useful minutes instead of a hand-wave.
Why a Dry Fast Changes the Drug Math
When you stop drinking, your blood volume drops, and that does two things to a medication. First, there is less fluid to dilute it, so the same amount of drug sits in a smaller space, which raises its concentration. Second, your kidneys, which clear a large share of drugs from your blood, slow down when they are short on fluid, so the drug leaves your body more slowly. A drop in renal clearance is the quiet mechanism behind most medication trouble on a dry fast (Roberts and Buckley, 2018).
Here is the part to hold onto, though, because it is easy to catastrophize: this does not happen with every drug. It matters most for three kinds. Drugs your kidneys clear rather than your liver. Drugs with a narrow therapeutic index, where there is not much gap between the helpful level and the harmful one. And drugs that themselves cut blood flow to the kidney. Learn to spot those three and you have most of the map. (Fasting also changes how your liver processes drugs, but not in one tidy direction, some pathways speed up and others slow, per Lammers et al. 2017, so "the fast slows your liver" is too simple to be useful.)
The One Class You Never Stop for a Fast: Benzodiazepines
If you take a benzodiazepine, Xanax (alprazolam), Valium (diazepam), Ativan (lorazepam), Klonopin (clonazepam), start here, because this is the most dangerous medication situation on this whole page, and the danger is the opposite of what people expect. It is not about taking it. It is about stopping it.
Benzodiazepines cannot be stopped abruptly. Your body adapts to them, and pulling them away suddenly can cause seizures, delirium, and dangerous swings in blood pressure and heart rate. This is not a mild rebound, it can be life-threatening, and the clinical guidelines are blunt about it: these drugs must be tapered down slowly under a prescriber's supervision, never stopped cold (Joint Clinical Practice Guideline on Benzodiazepine Tapering, 2025). So the idea of "pausing" your benzo to do a clean fast is genuinely dangerous. You do not pause it, and you do not skip a dose to keep the fast pure.
On top of that, benzodiazepines are processed by your liver and several of them, diazepam especially, stay in your system a long time, so their levels are among the least predictable to reason about when your whole physiology is shifting under a fast. Between the withdrawal risk and the unpredictability, this is the class where the answer is simplest: if you are on a benzodiazepine, a dry fast is a conversation to have with your prescriber before you change anything at all, and any dose change happens on their schedule, slowly, not on your fasting calendar.
Insulin and Diabetes Medication: Two Opposite Ways to Get Hurt
Diabetes medication is the other place people get into real trouble, and again it is because two failure modes point in opposite directions.
If you take insulin, or you have type 1 (insulin-dependent) diabetes, treat this as a hard stop: do not attempt a dry fast on your own. And just as important, never stop or skip your insulin in order to fast. For type 1 diabetes, stopping insulin is itself the emergency, not the fast: without it your body floods with diabetic ketoacidosis even on an empty stomach, and dehydration makes it worse and faster. It is tempting to think "I am not eating, so I do not need my insulin," but that is exactly the trap. International diabetes guidelines put insulin-treated people in the highest-risk group for any kind of fasting for precisely this reason (IDF-DAR, 2021).
There is a second, opposite danger. If you keep taking a normal dose of insulin, or a sulfonylurea (the pills like glipizide, glyburide, and glimepiride that push your blood sugar down whether or not you eat), with no food coming in your blood sugar can crash dangerously low. In studies of people fasting for Ramadan, symptomatic low blood sugar showed up in roughly one in five people on sulfonylureas (ADA Ramadan recommendations). So a normal dose can be too much and holding it can be too little, which is a needle only your prescriber can thread.
One more, because it is sneaky. The newer "-flozin" drugs (SGLT2 inhibitors like empagliflozin, dapagliflozin, and canagliflozin) can cause euglycemic DKA. Fasting and dehydration are known triggers, and the normal-looking glucose number is what makes it dangerous. The FDA put a specific warning on these drugs for exactly this (FDA, 2015).
When Being Dry Turns a Normal Dose Toxic
This is the dehydration group: the drugs that were fine yesterday and get riskier the moment you stop drinking.
Lithium is the textbook case. Its safe blood level sits very close to its toxic level, and your kidneys handle lithium almost like salt, so when you lose water and sodium on a dry fast, your body holds on to more lithium and the level climbs. The FDA's own lithium labeling warns specifically about dehydration and salt loss. Lithium and a dry fast do not mix without a doctor directly involved.
The same pattern shows up in a few other places worth knowing:
- Diuretics ("water pills"). Their entire job is to make you shed fluid and salt. Stacking that on a fast that already withholds water pushes dehydration and electrolyte problems in the same direction. (This applies most to the common loop and thiazide types.)
- Blood pressure medication. Fasting and dehydration lower your blood pressure on their own, so a blood-pressure drug on top can drop it too far: the lightheadedness, the dizzy-on-standing feeling, the near-faint. It does not happen to everyone, but the risk goes up, which makes it a timing-and-monitoring question for your doctor.
- NSAIDs (ibuprofen, naproxen). These reduce blood flow to the kidney, which is the one thing a dehydrated kidney cannot spare. Taken while dry, especially alongside an ACE inhibitor or ARB (common blood pressure drugs) and a diuretic, a combination clinicians literally call the "triple whammy," they can trigger acute kidney injury (Lapi et al. 2013).
- Digoxin, a heart medication with a narrow margin that leaves mainly through the kidneys, drifts toward toxic levels when you are dehydrated and low on potassium.
What's Actually Fine: The Other Half of the Title
The title promised you the "what's not dangerous" side too, because fearing everything is its own kind of wrong.
Thyroid medication is the clearest good-news example. Levothyroxine (T4) and liothyronine (T3) are actually meant to be taken on an empty stomach. Levothyroxine is absorbed better fasting than with food (Colucci et al. 2013), and thyroid hormone acts slowly enough that small shifts in timing are usually well tolerated. This is one of the least troublesome categories to fit around a fasting window. Two honest caveats, though: the goal is never to skip doses, because skipping is the real harm here, not timing, and these pills are normally taken with a little water, so confirm how to handle that on a dry day with your prescriber.
Beyond thyroid, a lot of ordinary once-daily medications can often be timed to your refeed window rather than stopped, with your doctor's sign-off. I am deliberately not handing you a blanket "safe list," because the safe answer depends on your specific drug and your specific body, and that is a doctor's call, not an article's. But the mental model is fair: most of your cabinet is a timing question, and only a handful are true danger.
Growth Hormone and T3: The Protocol's Own Rules
If you are working the Scorch Protocol, two of its own tools deserve a note, because their fasting interaction is specific.
Growth hormone first. Here is something people do not realize: fasting is one of the most powerful natural growth hormone releasers there is. A five-day fast raised growth hormone output several-fold in the classic study (Ho et al. 1988), driven largely by rising ghrelin as you go without food. That is a feature, not a bug, and it is a big part of why fasting drives repair. But it is also why you do not add injected growth hormone on top of a fast. Stacking injected hGH onto an already-surging system pushes it too high, into the territory of fluid retention, joint pain, and worse insulin sensitivity. And there is a second reason: injected growth hormone suppresses your own production while you are on it, working through IGF-1, so if you fast while still injecting, you actually blunt the very surge fasting is supposed to give you. The sound move is to come off injected growth hormone and let your natural axis rebound before you fast, never to run it through the fast. Medical caveat: that sequencing is guidance to work out with the doctor managing your hGH, not a dose I can hand you here or something to do on your own.
T3 is more individual. Because thyroid hormone is part of what a fast can suppress, there are specific cases where running a small amount of T3 through a fast makes sense and cases where it does not. That is genuinely case-by-case and belongs under supervision, it is one of the things the protocol adjusts per person rather than by a fixed rule. If your metabolism is the reason you are fasting in the first place, that whole question is worth reading up on in cellular hypothyroidism and T3 therapy.
The Five-Minute Prep That Makes This Safe
Here is the concrete thing to do before you fast, and it turns "talk to your doctor" from a brush-off into something genuinely useful.
Make a list of everything you take. Then, for each one, flag three things: does my kidney or my liver clear it, does it have a long half-life so it stays in me a long time, and is it one with a narrow margin for error. You can use anything to help build that list, including an AI assistant, to get a rough first pass on which of your drugs are the long-acting, liver-heavy, or narrow-margin ones. Then you bring that list to your doctor or pharmacist.
Two rules on that, because this is exactly where people go wrong. Treat the AI's output as a starting point for the conversation, not an answer, because it can be incomplete or flat wrong. And never, ever stop, skip, or change a dose based on it. The list is a map to hand your prescriber so they can tell you what actually changes. That is the whole job of the prep: walk in already knowing which two or three of your medications are the ones worth talking about.
Where to Take This
If you are a curious self-experimenter, the payoff behind all this caution is worth understanding. Start with what a fast is actually doing under the hood in dry fasting, autophagy, and regeneration, and if you are a woman, the rules are different enough to have their own piece.
But if you are reading this because you are on several medications and dealing with the kind of chronic illness that put you on them, Long Covid, ME/CFS, thyroid or autoimmune disease, this stops being a general question and becomes a personal one. That is exactly what the Scorch Protocol is built to map, in the right order and with supervision, and if you want your actual medication list looked at against your actual situation, that is what the members portal is for. Far better to have a real person help you sort the dangerous few from the harmless many than to guess at it alone.
(This article is educational and is not medical advice, and it is emphatically not a reason to start, stop, or change any prescription on your own. Fasting while on medication is a decision to make with the doctor who prescribed it. If you take insulin, a benzodiazepine, lithium, or any narrow-margin drug, do not fast without direct medical supervision.)