If a liter of IV saline left you feeling clear headed and steady on your feet, while it left someone else with crushing head pressure and a crash that lasted days, you have witnessed two genuinely different physiological pictures, not two different opinions about the same treatment. IV fluids are one of the more polarising topics in Long COVID and dysautonomia communities, and that polarisation makes sense once you understand what is actually happening underneath.
What the research actually shows Why IV fluids became part of Long COVID care When IV fluids tend to help When IV fluids can make symptoms worse Why the benefit often fades quickly Where viral persistence and antivirals fit A more useful way to think about your response Safer and more sustainable approaches When to ask for extra support Frequently asked questions
What the research actually shows
People with postural orthostatic tachycardia syndrome, or POTS, often genuinely have less blood in circulation than healthy people do. A study using radioactive tracer technology to directly measure blood volume found that people with POTS had a real deficit in both plasma volume and red blood cell volume compared with healthy controls, alongside a hormonal abnormality that should have corrected this but did not, as reported in this study on blood volume regulation in POTS.
On the helping side, a 2025 case series gave 22 people with ME/CFS and signs of dysautonomia three saline infusions over nine weeks and found significant improvements in quality of life, ability to work and POTS related symptoms, as described in this case series on intermittent saline infusion in ME/CFS. A separate patient reported outcomes study spanning both ME/CFS and Long COVID found that IV saline was among a small group of treatments where more than 40% of respondents rated it much better or moderately better, according to this large patient reported treatment outcomes study.
At the same time, a study in children with POTS found that a carefully balanced oral rehydration solution improved orthostatic tolerance and brain blood flow just as well as IV saline did, sometimes even slightly better, as shown in this study comparing oral rehydration solution with IV saline in POTS. That single finding goes a long way toward explaining why the simple question does IV fluid work does not have one answer.
Why IV fluids became part of Long COVID care
Many Long COVID symptoms overlap closely with POTS and other forms of dysautonomia. Dizziness on standing, a racing heart, near fainting and a heavy, foggy feeling in the head are all part of the picture.
Because increasing circulating blood volume is a recognised way to ease these particular symptoms in POTS, clinicians began trying the same approach in Long COVID. For some people it worked very well. For others it did not help, or made things worse. The difference usually comes down to what is actually driving someone’s symptoms underneath the surface, which is rarely identical from one person to the next.
When IV fluids tend to help
Genuine low blood volume
Some people with Long COVID and POTS appear to have a real, measurable shortfall in circulating blood volume. Part of the reason may be specific to this virus. SARS CoV 2 is known to bind to and downregulate the ACE2 receptor, which plays a role in fluid balance, and this downregulation has been proposed as one route to hypovolemia in Long COVID specifically, as discussed in this overview of Long COVID and POTS.
There is also a stranger hormonal piece to this puzzle. Normally, when blood volume drops, the kidneys release more of a hormone called renin, which should trigger a cascade that restores volume. In POTS this response is often paradoxically blunted, plasma volume is low but renin and aldosterone do not rise to correct it, as shown in the blood volume study referenced above. In this situation, IV fluids step in to do a job the body’s own hormones are failing to complete, at least for a while.
Autonomic dysfunction with otherwise healthy blood vessels
If someone’s main problem is blood pooling in the legs due to autonomic nerve signalling rather than damage to the blood vessel walls themselves, added fluid volume tends to behave fairly predictably. The vessels can still hold the extra fluid where it belongs, so circulation genuinely improves, at least for a while.
When IV fluids can make symptoms worse
Endothelial dysfunction and fluid leakage
The endothelium is the thin layer of cells lining every blood vessel, and it normally acts as a careful gatekeeper deciding what moves between the bloodstream and surrounding tissue. There is now a substantial body of evidence that this lining is damaged in Long COVID. Research has documented changes consistent with ongoing injury in endothelial cells months after infection, along with shedding of the protective glycocalyx layer that normally helps hold fluid inside the vessel, as outlined in this review on endothelial barrier damage in Long COVID.
When this barrier is compromised, added fluid does not necessarily stay where you put it. It can shift into surrounding tissue instead, which may explain reports of head pressure, swelling, chest discomfort or a delayed worsening that some people notice hours after an infusion rather than during it.
Microcirculation and capillary rarefaction
Even if total blood volume rises, oxygen delivery ultimately depends on the smallest vessels, the capillaries. A study using video microscopy under the tongue found persistently reduced capillary density in people with Long COVID months after infection, alongside slower recovery of blood flow after a brief test occlusion, as shown in this study on capillary rarefaction in Long COVID. Separately, a study from Tunisia using finger thermal monitoring found that endothelial dysfunction itself was an independent risk factor for ongoing Long COVID symptoms.
In simple terms, if the smallest vessels are not distributing flow properly, adding more volume upstream does not guarantee it reaches the tissues that need it. For some people it may simply add pressure without adding function.
There is also a recognised subtype of POTS, sometimes called hyperadrenergic POTS, where the nervous system is already running on excess adrenaline. In this group, clinicians have specifically raised concern that expanding blood volume could push blood pressure too high rather than stabilising it, which is one more reason a one size fits all approach to IV fluids does not work.
Kidney and electrolyte sensitivity
SARS CoV 2 has been shown to cause specific dysfunction in the proximal tubule, a part of the kidney responsible for reclaiming the bulk of filtered electrolytes and small molecules back into the bloodstream, as discussed in this review on possible kidney involvement in Long COVID. Standard blood tests mostly measure how well the kidneys filter, not how well they fine tune electrolyte handling afterwards, so this kind of subtle dysfunction can easily be missed even when labs look entirely normal.
Rapidly shifting fluid volume through an IV can interact with this fragile balance in ways a quick blood test will not necessarily catch, which may help explain palpitations, weakness or headaches that some people notice after an infusion.
Why the benefit often fades quickly
Even when IV fluids genuinely help, the relief is usually temporary. Existing international guidelines on POTS specifically caution against routine, repeated IV saline because there is not enough safety evidence to support it as an ongoing treatment, a point raised directly in the case series on saline infusion in ME/CFS referenced earlier.
This is an important clue rather than a disappointment. Fluids can support circulation for a few hours or days. They do not repair a damaged endothelial lining, resolve ongoing inflammation or reset autonomic regulation. They offer support, not a cure, and how quickly the benefit fades is itself useful information about what is and is not being addressed.
Where viral persistence and antivirals fit
None of this happens in isolation from a wider question many people with Long COVID ask, whether ongoing viral activity is part of what is driving their symptoms. There is real evidence that fragments of SARS CoV 2 can persist in tissue well beyond the acute infection, which has made antiviral treatment an active area of research.
The results so far have been more disappointing than hoped. A trial at Stanford testing a 15 day course of the antiviral Paxlovid in 155 people with established Long COVID found no improvement in fatigue, brain fog, body aches or other symptoms compared with placebo, as reported in this study on Paxlovid and Long COVID outcomes. A much larger NIH funded trial called RECOVER VITAL tested both 15 and 25 day courses in nearly 1,000 participants, and early reporting in 2026 indicates this longer course also failed to significantly improve symptoms compared with placebo, according to coverage from The Sick Times on the RECOVER trial results, although a fuller analysis of viral markers in participants’ blood has not yet been published.
This does not necessarily close the door on viral persistence as a contributing factor for some individuals, and smaller case series of people taking extended antiviral courses outside formal trials have reported meaningful improvement for some, though not all, participants. For now though, the population level antiviral evidence has been underwhelming, and this is not yet an established treatment to expect from a course of antivirals alone.
A more useful way to think about your response
Instead of asking whether IV fluids work for Long COVID, a more useful question is what your particular response says about what is happening underneath.
A few things are worth paying attention to. Did you feel clearer and steadier, or simply heavier and unwell. Did the benefit last hours, a day, or barely outlast the drip itself. Did symptoms worsen immediately, or did they creep in later that evening or the next day.
None of these responses are random. They are clues about whether your situation looks more like straightforward low volume, more like a vascular or endothelial problem, or some mixture of the two.
Safer and more sustainable approaches
For many people, oral fluids with a properly balanced electrolyte mix are a steadier and lower risk starting point than IV saline, and the evidence for this is more solid than many people expect. In the pediatric POTS study mentioned earlier, a balanced oral rehydration solution matched or slightly outperformed IV saline at improving orthostatic tolerance and brain blood flow during a controlled test.
Plain water alone is not the same thing. Solutions designed for oral rehydration contain a specific balance of sodium and glucose that helps the gut absorb and retain fluid rather than simply passing it through.
Beyond hydration itself, the more durable gains tend to come from addressing what sits underneath, supporting autonomic regulation through compression and careful pacing, addressing inflammation where it is genuinely active, and working with a clinician familiar with post viral illness on whether medications that support blood vessel tone or blood volume, the kind already used for POTS more broadly, might be appropriate for your specific picture.
When to ask for extra support
It is worth raising IV fluids with a clinician, ideally one familiar with POTS or post viral illness, rather than pursuing them informally. This matters particularly if you have a heart, kidney or blood pressure condition, if you suspect hyperadrenergic POTS, or if previous infusions have left you feeling measurably worse rather than better. Your own pattern of response is genuinely useful diagnostic information, worth bringing to that conversation rather than puzzling over alone.
IV fluids are not a universal answer for Long COVID, and they were never meant to be. They are a physiological tool that interacts differently with different underlying problems, low volume, vascular dysfunction, kidney sensitivity, autonomic imbalance, sometimes more than one at once. Paying close attention to how your own body responds, and bringing that information to a clinician rather than treating it as a verdict on the treatment itself, is often more useful than the infusion alone.
Why Patients Report Such Different Experiences
One of the most confusing aspects of Long COVID is watching two people receive the same treatment and report completely different outcomes. One person may feel clearer, steadier and more functional after IV fluids, while another develops head pressure, worsening fatigue or a delayed crash. These experiences are not necessarily contradictory. They may reflect different underlying mechanisms driving symptoms. Long COVID is not a single disease process, and responses to treatments often provide clues about what is happening beneath the surface rather than simple proof that a treatment works or does not work.
Frequently asked questions
Why do IV fluids help some people with Long COVID but not others?
Because Long COVID affects circulation in different ways from one person to the next. Some people genuinely have low blood volume that fluids correct temporarily, while others have damage to blood vessel linings or the smallest vessels, where extra volume does not translate into better blood flow.
Why do I feel worse after IV fluids rather than better?
In some people, fluid does not stay reliably inside the bloodstream and shifts into surrounding tissue instead, which can show up as head pressure, swelling or a delayed crash hours later. This points toward vascular or endothelial involvement rather than simple dehydration.
Should I avoid IV fluids if I have Long COVID?
Not necessarily. Many people genuinely benefit, particularly when low blood volume is the main driver. The more useful question is whether your situation looks like a volume problem or a circulation problem, which is worth exploring with a clinician.
Why does the benefit from IV fluids not last?
Because fluids support circulation for a limited window rather than fixing the underlying cause. They do not repair damaged blood vessel linings, resolve ongoing inflammation or correct autonomic dysfunction.
Are oral fluids a safe alternative to IV saline?
For many people, yes. A study in POTS found that a properly balanced oral rehydration solution worked as well as IV saline at improving blood flow during an orthostatic challenge, with fewer risks attached.
Is this related to POTS?
Often, yes. Long COVID and POTS overlap significantly, and many people with Long COVID who respond well to IV fluids are showing a pattern consistent with hypovolemic POTS specifically
Do IV fluids treat Long COVID itself?
No. IV fluids do not address the underlying condition. They can temporarily ease specific features such as low blood volume or orthostatic intolerance in some patients, without correcting whatever is driving Long COVID as a whole.
Why might my blood volume be low even though my blood tests look normal?
Standard blood tests do not directly measure circulating blood volume. Specialised studies using tracer techniques have found genuine deficits in plasma and red blood cell volume in POTS that routine bloodwork would not pick up.
Do antivirals help with Long Covid symptoms?
The evidence so far has been disappointing. Large trials testing extended courses of the antiviral Paxlovid for Long COVID have not shown significant improvement compared with placebo, although research into viral persistence as a contributing factor is still ongoing.
What is endothelial dysfunction and why does it matter here?
The endothelium is the lining inside your blood vessels that controls what moves between blood and tissue. When it is damaged, which research has documented in Long COVID, fluid can leak out of circulation instead of staying where it is needed.
Is it safe to use IV saline regularly for Long COVID symptoms?
Current consensus guidelines for POTS specifically advise against routine, repeated IV saline because there is not enough long term safety evidence, even though occasional or short term use can genuinely help some people.
How do I know if IV fluids might actually help me?
Paying attention to your own pattern of response is a good starting point. Clear, steady improvement that lasts at least several hours points toward low volume. Heaviness, head pressure or a delayed crash points toward something more vascular, which is worth discussing with a clinician before trying fluids again.
This article is for general information and education. It does not replace personalised medical advice. Decisions about IV fluids, antivirals or any other treatment should be made together with a qualified clinician who knows your individual history.
Sources and further reading
Blood volume and POTS Renin and aldosterone regulation of blood volume in POTS: https://pubmed.ncbi.nlm.nih.gov/15781744/ Long COVID and POTS, including ACE2 and hypovolemia: https://www.standinguptopots.org/longCOVID Intravenous fluids guide and infusion protocols for POTS: https://www.standinguptopots.org/resources/iv-saline
IV saline evidence Case series on intermittent saline infusion in ME/CFS and dysautonomia: https://pmc.ncbi.nlm.nih.gov/articles/PMC12318745/ Oral and intravenous hydration in orthostatic hypotension and POTS: https://www.sciencedirect.com/science/article/pii/S1566070222000108 Large patient reported treatment outcomes study in ME/CFS and Long COVID: https://www.pnas.org/doi/10.1073/pnas.2426874122 Oral rehydration solution compared with IV saline in pediatric POTS: https://pubmed.ncbi.nlm.nih.gov/31405524/
Vascular and kidney mechanisms Endothelial barrier damage and its contribution to Long COVID: https://link.springer.com/article/10.1007/s10456-023-09878-5 Persistent capillary rarefaction in Long COVID: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9366128/ Microcirculation and endothelial dysfunction in Long COVID, a Tunisian cohort: https://www.frontiersin.org/journals/cardiovascular-medicine/articles/10.3389/fcvm.2021.745758/fullVascular complications of Long COVID, a systematic review: https://www.mdpi.com/1422-0067/27/1/433 Possible kidney involvement in Long COVID: https://pmc.ncbi.nlm.nih.gov/articles/PMC10106649/
Viral persistence and antivirals Paxlovid and Long COVID outcomes, including the STOP PASC trial: https://pmc.ncbi.nlm.nih.gov/articles/PMC12445499/ The Sick Times on early RECOVER trial results including RECOVER VITAL: https://thesicktimes.org/2026/05/12/recovers-first-round-of-clinical-trials-are-failing-will-the-next-phase-be-better/
Disclaimer
This article is for educational purposes only and does not replace medical advice. Individual treatment decisions should be made in consultation with qualified healthcare professionals.