Can I Take This? Supplements, creatine, recreational drugs and Kidney Health

The For Kidneys Sake podcast series is brought to you by Imperial College Healthcare NHS Trust and North West London Integrated Care Board (NWL NHS).

Welcome to For Kidneys’ Sake! The new name for our podcast series is previously known as The Rest Is Kidneys. In this first episode of our new 20-part series, Prof Jeremy Levy and Dr Andrew Frankel return to tackle a topic that crops up frequently in both clinic and primary care: supplements, herbal remedies, and recreational drugs and what they really mean for people with chronic kidney disease (CKD).

This episode explores everything from high-dose vitamins and gym-related creatine use to the dangers of anabolic steroids, ketamine, and certain traditional herbal medicines. With their usual clarity and clinical insight, Jeremy and Andrew offer practical advice for clinicians and thoughtful guidance on how to approach these often-overlooked areas of patient care.

Key Takeaways:

1. Ask directly about supplements, herbs, and non-prescribed products – especially in anyone with reduced kidney function or a CKD diagnosis. These are often missed unless specifically asked about.
2. Standard multivitamins are safe in CKD, but high-dose vitamin C and extra vitamin D can be harmful, especially when kidney function is already reduced.
3. Creatine, high-protein diets, and muscle mass can raise creatinine without indicating CKD. Use a urine dipstick, ACR, blood pressure, and ultrasound to assess properly.
4. Anabolic steroids and ketamine carry serious risks, including nephrotic syndrome and irreversible bladder damage. These are increasingly common but poorly understood dangers.
5. Herbal remedies are not without harm – some are directly nephrotoxic, others interact with prescribed treatments. These should be avoided in CKD, but conversations must be handled with care and cultural awareness.

This opening discussion sets the tone for the series: practical, collaborative, and focused on bridging gaps between clinical insight and everyday patient care. Supplements and herbal products are everywhere, and understanding their impact is more important than ever for improving kidney health.

References: 

Creatine and kidneys:  Nutrients 2023, 15, 1466.   doi.org/10.3390/nu15061466 

Herbal medicines and CKD; Nephrology 15 (2010) 10–17   doi:10.1111/j.1440-1797.2010.01305.x 

Herbs and more: Drug stewardship for people with chronic kidney disease; towards effective, safe, and sustainable use of medications:  Nat Rev Nephrol. 2024 June ; 20(6): 386–401. doi:10.1038/s41581-024-00823-3 

Resource Links:
NICE GUIDELINES [NG203] chronic kidney disease: assessment and management Overview | Chronic kidney disease: assessment and management | Guidance | NICE

Northwest London CKD guidelines for primary care

The purpose of this podcast is to inform and educate health care professionals working in the primary care and community setting. The content is evidence based and consistent with NICE guidelines and North West Guidelines available at the time of publication.

The content of this podcast does not constitute medical advice and it is not intended to function as a substitute for a healthcare practitioner’s judgement.

Produced by award-winning media and marketing specialist Heather Pownall of Heather's Media Hub

Transcript

Jeremy Levy

Hello, I'm Jeremy Levy, consultant nephrologist at Imperial Healthcare NHS Trust, and it's a real pleasure to be back with you for our second series of podcasts, All Things Kidney. Many of you will remember the first series were The Rest Is Kidneys. We've had a change of title, we're now, For Kidney’s Sake, brilliant new title for brilliant new set of episodes, all things kidney related. And I'm delighted to be joined again by my good friend, Andrew.

Andrew Frankel

Hello there everyone, I'm Andrew Frankel, a colleague of Jeremy's who works, also, at Imperial College Healthcare NHS Trust. So this week in our expanded series of podcasts about kidney health, we're going to talk, or we're going to focus on nutritional or dietary supplements, herbal remedies, and possibly even we'll move into recreational drugs. Because, in fact, we get a lot of questions about these, and we see many individuals who are actually taking a wide range of these supplements.

Jeremy Levy

I completely agree, Andrew. And it's not a rare issue at all. I mean, we get emails at least two or three times a week that cover this range of topics. And, actually, it seems to be increasing. And many studies have demonstrated that in people with chronic kidney disease, herbal remedies, dietary supplements, and the like are being used in anything between 25 % and 70 % of people with known chronic kidney disease, and in some populations, even more than that, depending on where the studies are done.

Andrew Frankel

Well, Jeremy, I suspect you know much more about this than I do, but from my perspective, the starting point is always to ensure that we specifically ask the patient about this when we take a history and talk to them.

Jeremy Levy

That's of course exactly right, Andrew. Back to medical school, take a good history. But it's easily forgotten, and we know we're all pressured. In someone, especially with chronic kidney disease, it is vital to ask not just about their prescribed medications, but supplements and herbs, anything they buy over the counter at chemists or health shops. And things like supplements are not medicines as perceived by people, the population, and they're not bought at chemists.

So, really need to ask these questions and use those words. People don't mind the word supplements, but even asking about things like vitamins, nonsteroidal anti-inflammatories, that everybody should know about, and, of course, you buy these over the counter. They're widely used because they're effective and generally they're safe. But in people with chronic kidney disease, we want to know about them. So asking about these things is absolutely critical. Use the words vitamin supplements, extra painkillers.

For some things like vitamins, which we'll come to in a moment, it's often about the dose. So you do need to know something about what the normal range of doses for some things. And for herbal remedies, this gets very difficult because neither you nor I, nor most healthcare professionals will know what the names of the herbs are. There's a vast range of products out there. Many of them are bought overseas and have names that we won't even be familiar with. And the patient, the person using these may also not be familiar with what the contents are, and the labels are often unhelpful.

Andrew Frankel

So Jeremy, remembering about non-steroidals, easy. But let's take these all in sequence. So let's start with vitamins. Tell me a little bit more about vitamins: aren't routine vitamin supplements safe in CKD?

Jeremy Levy

So, yes, standard doses of most vitamins as, for example found in multivitamin tablets, which are what generally people use, are all safe in chronic kidney disease. They might be they might not be needed, they might not be efficacious because a good healthy diet with lots of fruit and vegetables actually provides you with plenty of vitamins, but they're generally safe. The one to be careful about is people with known CKD, chronic kidney disease, using additional vitamin D, if they're already prescribed, for example, alpha-calcidol, which is an active vitamin D. 

There's this difficult balance about whether or not they need extra vitamin D and that needs discussion almost certainly with a kidney doctor. And that's the risk around vitamin D, of the routine vitamins. Vitamin C has one problem, and that's the mega dose vitamin C, which are the large effervescent tablets that some people like.

They contain a thousand milligrams of vitamin C, and the normal recommended daily dose is a hundred milligrams, that's 10 times as much. And vitamin C, which is ascorbic acid, is metabolised to oxalic acid or oxalate, which can form kidney stones, but is also excreted through the kidneys. So if you have chronic kidney disease, taking these very high doses of vitamin C can contribute to kidney toxicity, and kidney stone formation. So that's very important. So people with CKD definitely avoid the big 1000 milligrams dissolvable vitamin C tablets. 

And finally, some very small number of people, but people who are trying to build body mass, bodybuilders, people going to gyms, there's a bit of a vote for using mega doses of vitamins A, D and E in combination.

And those are not good if you've got chronic kidney disease. And that's particularly the D, but high dose vitamin A is not good for that. But that's actually not a common problem.

Andrew Frankel

So, essentially, people with CKD should avoid high-dose vitamin C, particularly if their GFR is below 30, and be careful about vitamin D if they're also taking activated vitamin D. Again, that's likely to be when their GFR is less than 30. Now you mentioned bodybuilders, and I would say to you that this is a very common referral that I see in the nephrology clinic and through our virtual service. Can we talk a little bit more about them?

So they are generally the younger people, more often men, but not always, going to the gym daily, weight training to put on muscle. And this is all about when a measured creatinine in someone who is apparently healthy is high. For example, 140, equating to a GFR that may be 50.

So we get a lot of questions about people who we identify as being bodybuilders with these abnormalities. They're often taking supplements, particularly creatine, and they're often using high protein diet. Tell me, Jeremy, and be interested to know what is your view about how we should approach this?

Jeremy Levy

Absolutely. You've asked me about three questions in one there. The critical thing is have they got kidney disease or not? And bodybuilder doesn't have to be a professional. This could just be somebody going to a gym five days a week, doing weight training and as you say, taking high protein diets and creatine supplements, and suddenly you've got a creatinine of 1.40 and a GFR of 50. They've never had a blood test before. So let's go through those bits slightly separately. 

So first of all, remember how that EGFR is calculated. It's calculated by measuring the serum creatinine, and then that's converted into the EGFR by a bit of maths. The creatinine comes from muscle. So anybody with higher muscle mass will have a higher serum creatinine, regardless of what else they're eating, supplements they're taking. They may have completely normal kidneys, but a higher creatinine will translate into a slightly lower EGFR.

So, simply from muscle mass, you might well have a lower EGFR, estimated GFR, and nothing to do with your supplements, and that's just about your muscle mass. Secondly, eating a high protein intake and particularly, actually, cooked meats. And lots of these people just eat, for example, two or three chicken breasts a day that they've grilled, so cooked meat. That is muscle, and cooked meat is converted into creatinine and creatine. That's why the bodybuilders, people going to the gym take it. But eating a cooked meat diet will push up your creatinine. 

And finally, as you mentioned, creatine supplements which are widely used now by athletes in many sports. There is actually interesting and growing evidence that in the sports literature, they are beneficial for all sorts of activities of muscle, they improve muscle energy as well as muscle bulk. So, some evidence of why people are taking creatine, and it comes in the form of creatine phosphate.

But in some people, this is converted somewhat idiosyncratically, so not in everybody, into creatinine. So, people taking creatine supplements might have higher blood creatinine levels. So all of that forms a mess that this young person, may not be young, but usually are, going to a gym, weight training, has muscle bulk, eating protein, and eating creatine, all can cause confusion.

Andrew Frankel

So Jeremy, absolutely. Thanks for covering all this, but now tell us, how do you unpick this if you are looking at this individual in primary care?

Jeremy Levy

So that is the critical question. So I think there are three extra things. The question you're asking is, have they got kidney disease or not? So first of all, make sure you've asked the questions, okay. Are they taking creatine supplements? Are they eating a high protein diet? The one quick rider, lots of these people are also using anabolic steroids. People doing weight training in gyms, about 30 % do also use anabolic steroids. And then the two other critical things to look for kidney damage is the urine.

Dipstick the urine. None of these things, body weight, creatine supplements should cause urine abnormalities. So dipstick the urine. If this is going to be, essentially, an artifact of supplements and muscle, there should be no blood and no protein in the urine. So dipstick the urine. Send the urine ACR as well because you might not have picked up low level proteinuria, and measure the blood pressure.

Because if somebody's got no kidney disease, no kidney damage, they'll have nothing in their urine and their blood pressure should be normal. With one minor caveat, the anabolic steroids can sometimes push blood pressure up. And it is worth doing an ultrasound. This might be somebody who's got congenitally abnormal kidneys and therefore they've got a reason for having an abnormal kidney function. But then, if you've got this young person who says - happily tells you that they're weight training - they've got normal blood pressure, a normal kidney ultrasound, and nothing in their urine, and you're aware they're well-muscled using creatine supplements, then that creatinine of 140, GFR of 50, is going to be from their supplements, and not because they've got kidney disease. 

So urine, blood pressure and ultrasound are really, really helpful. There are some people where we're still a bit unsure, particularly if that GFR is even lower. Let's say it's 45 and you want to be certain.

And there is other things we can do, which almost always needs referral. That's - the test we used to do was a nuclear medicine, or an isotopic GFR. It's a gold standard test of kidney function that doesn't rely on muscle mass. There is a blood test now called a Psi Statin C, which we can also use independent of muscle mass, but in the UK not routinely available everywhere, though around the world, it is often fully available to lots of healthcare staff. So those two tests can be used to distinguish

Is this a problem of muscle mass and supplements versus genuine reduced GFR? And then the last thing I think on this point, some people suggest, why not just ask the person to stop taking their creatine for a couple of weeks and re-tech it? It's not just the creatine supplement. If you're 100 kilograms and you're pure muscle, it's also your muscle mass. And of course, that won't have changed in two weeks. So that's generally not such a helpful tip to try and unpick this issue. It's the urine, the blood pressure, and then the ultrasound.

Andrew Frankel

Jeremy, that's really helpful. An area that I know that you and I have disagreed on in the past is should these individuals, when you've determined they do not have kidney disease, should they continue to take creatine supplements? Because I've always tended to say no.

Jeremy Levy

I'm sensing a softening in your approach here, actually Andrew, maybe I've convinced you over the last few years. So my reading of all of the literature is I can see no evidence that creatine is harmful to kidneys. Yes there have been isolated case reports of people undoubtedly getting intercisal nephritis, which is an allergic reaction to a drug or a supplement or a product in the kidneys. So there are isolated case reports but there are tens of millions of people using creatine supplements. 

There are a very large number of studies now, mostly from sports science, but with very large numbers of healthy people taking creatine which have shown no harmful effects on kidney function, or on any other abnormalities in a very large number of studies. And in animal models of animals with normal kidney function no harm has ever been found.

There has been a little bit of evidence in some animal models of chronic kidney disease that, potentially, creatine can worsen it. So normal kidneys that - in my view no evidence of harm but I wouldn't advise anybody with chronic kidney disease to be using creatine supplements.

Andrew Frankel

Jeremy you're making this now much much easier for me to understand and to perhaps adjust the way I've approached this. So, work out first if the individual has underlying kidney disease, or if the abnormal GFR is an attribute of their muscle mass, diet, or creatin and then you would only stop the creatin if you identify actual kidney disease. 

I would just highlight that we do need more information about what is the dose of creatine that's actually beneficial, and if we are going to start using - seeing people using this, we need to give them better advice on how to use this. But can I now also ask you, as you mentioned in passing, anabonic steroids. Tell us a little bit more about that in kidneys.

Jeremy Levy

Yeah.

Yeah, sure. So as I said, they are sadly widely used in people building muscles, so they're particularly widely used in anybody competing, bodybuilders trying to compete. But it turns out that actually, as I said, about 30 percent of gym users who are really trying to build muscle use anabolic steroids in most countries. It's absolutely right. And of course, the situation is slightly worsen because people competing then do things like use diuretics at the time of competition. So they're doing multiple things that might be harmful for kidneys. 

Anabolic steroids are bad. They're bad all full stop. They do build muscle back, but they have multiple adverse effects on hormone profiles, testosterone, on the liver. So outside of kidney disease, they have a variety of negative effects on particularly on the endocrine system, bones, et cetera. 

Kidney-wise, the one problem is that, not commonly, anabolic steroids have been associated with an acute nephrotic syndrome. So, where kidneys - where you pee huge amounts of protein, the kidneys leak protein, and there's a particular pattern we see on the kidney biopsy. If you're really interested, it's called FSGS, focal segmental glomerulosclerosis. It's not common, but that would be detected by protein in the urine, and not just a bit, a lot. It's nephrotic. 

So this ACR, albumin-creatinine ratio is more than 300, very high, and people usually have a kidney injury as well. The GFR isn't a bit low, it drops down to 30 and 20. And it can only get better by stopping the anabolic steroids, and it reoccurs often with re-challenge. It's not common, but it's a problem with anabolic steroids.

Andrew Frankel

So, definitely anabolic steroids are not good. They can cause proteinuria. 

But let's move away from the gym. And what about other recreational drugs? Are there any that are specifically bad for the kidneys, that we need to question about?

Jeremy Levy

I'm going to assume Andrew this isn't about personal advice about what you should be buying down your High Street.

Andrew Frankel

I'll ask you about that after the podcast.

Jeremy Levy

Yes, yes, yes, there are a variety of of kidney-toxic recreational drugs that people are using, and the one I really want to mention for this audience is ketamine. So ketamine is a widely used drug which is growing in popularity. 

It's growing in popularity in all ages, but particularly younger people, because it's perceived as being non-addictive, and it's cheap, and it's grown in the last 10 years. And in fact it's not nephrotoxic, it's bladder-toxic, but it is a real problem in a minority of users, and it causes an interstitial cystitis, inflammation in the bladder wall. But this becomes irreversible, and it picks off the lower ends of the ureters, and leads to an obstructive nephropathy. 

So the ureters get picked off, narrowed, and the kidneys get obstructed. And the chronic inflammation in the bladder causes severe chronic lower abdominal and pelvic pain. And in users, there's a term for this called ket cramps, ketamine cramps. The problem is often irreversible. It's terrible. People pee blood sometimes, and debris in their urine, and people, if they get this, often need cystectomies or permanent catheterisation; it is truly horrible. So, ketamine and bladder, really bad state of affairs, but not common, but a significant minority of people get it. 

And then of the other recreational drugs, cocaine can do two things. Cocaine can cause chronic renal ischemia. Many of you will be aware, young people with chest pain, cocaine can cause cardiac vasoconstriction. In the kidneys, it can cause vasoconstriction and ischemia. And very rarely there's a problem that cocaine can actually cause vasculitis in the kidneys, almost always with a skin rash - ears, stomach, thighs - a vasculitic skin rash. 

And lastly, some of the less widely used drugs, but older drugs, injectable drugs like heroin, they can cause, of course, all sorts of viral diseases by sharing needles, which all affect the kidneys and, rarely, amyloidosis. But the ones to remember, I think now really, are ketamine for this horrible bladder problem.

Andrew Frankel

Well, Jeremy, I really know who to come to if I want to get information on recreational drugs, so thank you very much.

We've talked about vitamins, we've talked about supplements. Let's come on now to herbs, because herbs are widely used, and people think of them as safe, they think of them as not drugs, and there are particular cultural traditions associated with their use, particularly in relation to people from China, or using Chinese herbs, and India. So what about herbs and the kidneys? Because I am aware there are specific issues here.

Jeremy Levy

So yes, this is exactly as you say, a complex area and often we don't know what's in the herbs and the dressing. This is very, very important. But of course, why are people taking herbal remedies is an important consideration too. They're often suspicious of Western medicine. They're suspicious of the pharmaceutical industry. People think herbs are safe, they're natural products, and they think they're going to be effective, they think that their local herbalist isn't corrupted by big pharma.

So there are all those psychosocial reasons, and cultural reasons, that people absolutely think these are going to be, if not efficacious, harmless. But there are lots of problems. Of course, herbs are just plants full of chemicals. They are just a variety of things in there, and most of the time people don't know actually what they're getting. They don't know whether the product is a pure plant of one species or another, or is in fact a mixture. So there are potentially lots of problems.

There are some herbs that are definitely nephrotoxic, and the best example is a herb called Aristolochia, that is not meant to be prescribed by herbalists. They know that this is kidney-toxic, but this is a clematis family plant, and there's no reason it can't grow as a weed, by a field growing something that a herbalist may want to use. And in fact, there was an epidemic of this herb causing irreversible kidney failure in Belgium in the late 1990s and a hundred women taking this for weight loss all ended up on dialysis. It was a terrible outbreak. 

So a plant product getting into a herbal mix when it's known to be nephrotoxic, that's not common, but really important. But the herbs that people are taking, they in the end don't know what they're getting, and that's a problem. And then there's epidemiological data from lots of countries, but the best comes from, actually, China, and Taiwan, and Thailand, that people taking regular herbal preparations of all sorts have a higher risk of chronic kidney disease. 

So even though they might think they're taking these herbs to prevent chronic illness, actually there's an association with more chronic kidney disease. So I would be advising people with, especially if they've got known chronic kidney disease, to be avoiding all herbal remedies. 

And then I'm not going to go through a whole list because most of us don't know what people are taking, but the two or three other things:

Licorice, licorice root, not licorice as in licorice all sorts of sweets which are full of sugar, but licorice root, quite a lot of people like chewing, is a problem because it can cause hypokalemia - low blood potassiums - and chronic hypokalemia causes tubular damage and chronic kidney disease. So no licorice root chewing. 

And more more popular, people like buying dried mushrooms and mushroom powders and there are two very toxic families of mushrooms: the Cortinaris family, and the Amanita family. So being careful about what mushrooms you eat, and your packet of magic mushrooms that you bought in Portobello Road might contain a toxic mushroom. Now, mushroom collectors say they can recognize these, but who knows? 

And then there are a list of other things. Fish gallbladder and snake gallbladder are nephrotoxic, but used in Chinese herbal products in Southeast Asia. A starfruit is neurotoxic if you've got chronic kidney disease. So these isolated examples, and fundamentally, if you've got chronic kidney disease, avoid herbal preparations. 

Lastly, they might interact with your good medicines that you're taking, your statin, your SGLT2 inhibitor, your ACE inhibitor. Your herbal preparation may interact, which may also lessen the efficacy of the prescribed medicine that might be genuinely helping you. But, Andrew, we do need to be very careful in this conversation.

Why is this person using a herbal product? Us just blundering in and saying “stop taking it, it's rubbish” is not going to build confidence between us, a healthcare professional and the patient. So we do need to approach these in a way that can maximise our engagement with the patient.

Andrew Frankel

Jeremy, that was absolutely superb. I had no idea of the range of agents that can actually damage the kidney, and your knowledge about all this. I want to try and summarise this and think about some key messages that people can take away. 

The first is, of course, that we must ask all people who have been identified with an abnormal GFR about all the medicines, and all the supplements, and all the agents they may be taking, and we must explicitly include herbs, supplements, and vitamins, even high dose vitamin C. 

The second is that we will see people who are building muscle who have got high creatinine, and falsely positive low GFR because of their muscle bulk, the use creatinine supplements, and high protein diet. And in these individuals, it's important in the first instance to consider, could they have underlying kidney disease, check their urine, do their blood pressure, do an ultrasound. And if this is all normal, you may then consider that they probably have got an abnormality of their GFR caused by their lifestyle rather than CKD. And also the important point you highlighted that creatine supplement is not itself nephrotoxic. 

I think I'm very clear about the fact that we should stay away from anabolic steroids and ketamine and these are useful messages just to ensure that the population know about these adverse events that are really very poorly signposted. 

And finally, herbal remedies, frequently used, is not something that people with CKD should be using. We should be discouraging it, but we should be doing that in a manner that includes a careful dialogue with our patients. 

So really, I've learned a huge amount, Jeremy, that's going to help me in my practice. Thank you so much.

Jeremy Levy

Andrew, it's been a pleasure. I'm sure you'll be able to teach me lots in our next episode. As always, a joy to be with you.