You need IV fluids when dehydration is severe, or when you can't get enough fluid in by mouth because it won't stay down or can't keep up with what you're losing. Short of that, drinking the right way treats it. So the question to ask yourself isn't how rough you feel. It's whether fluid is staying down and keeping up, and whether any of the warning signs below have shown up. When an IV is needed for those reasons, MedlinePlus and the CDC describe it being given in a hospital or clinic.
The signs that sort out your next step
The signs tell you more than the feeling does. MedlinePlus says that if you notice dehydration and treat it quickly, you should recover completely, and for mild cases treating it means drinking. A few specific signs mean you've moved past what drinking at home should handle. They fall into three groups, and each group has its own next step. If a headache is your main symptom, a dehydration headache has its own warning signs, and they are worth checking too.
Signs you can treat by drinking
MedlinePlus lists these as signs of mild to moderate dehydration:
- Thirst
- A dry or sticky mouth
- Not urinating much, and darker yellow urine
- Dry, cool skin
- Headache
- Muscle cramps
With these alone, the next step is to drink, the way the next two sections explain.
Signs to get medical care for right away
These are the signs MedlinePlus gives for severe dehydration, along with the points at which it says to contact a provider or seek medical care:
- Not urinating at all, or very dark yellow or amber urine
- No urine for 8 hours or more
- Dizziness or lightheadedness, or feeling faint
- A rapid heartbeat or rapid breathing
- Sunken eyes, listlessness or irritability
- Being unable to keep any fluids down for 12 hours or more
- Vomiting for longer than a day, or 3 or more times in one day
Any one of these is a reason to call your doctor or go to an emergency room. It isn't a reason to keep trying at home, and it isn't a reason to book a drip at home.
When to call 911
MedlinePlus says to call 911 if the person:
- Loses consciousness at any time
- Has any other change in alertness, such as confusion or a seizure
- Has a fever over 102°F
- Shows signs of heatstroke, such as a rapid pulse or rapid breathing
- Doesn't improve, or gets worse, despite treatment
Call 911 too if you think the vomiting comes from a poison, or if there is blood or dark, coffee-colored material in the vomit.
How to rehydrate after vomiting
After you've been sick, the instinct is to drink a big glass of water. That's the mistake. MedlinePlus warns that forcing down a large amount at once can bring on more vomiting. Small amounts taken often are what stay down.
What you drink matters too. An oral rehydration solution, sold at drugstores as a powder or a ready-made drink, puts back minerals as well as water. MedlinePlus advises against fruit juice, soda, gelatin and broth while you're sick, because they don't replace lost minerals and can make diarrhea worse.
- Start small. MedlinePlus suggests 2 to 4 ounces (60 to 120 mL) every 30 to 60 minutes.
- If even that comes back up, suck on ice cubes. It's one of the first steps MedlinePlus lists.
- Know where home care stops. If you hit any sign in the right-away list above, especially fluids that won't stay down for 12 hours, stop trying to push through.
When fluids won't stay down, MedlinePlus says you may need fluids through a vein. That decision belongs with a provider or a hospital. If you're weighing a drink against a drip for milder cases, IV fluids and electrolyte drinks compared goes through the difference.
How to rehydrate after diarrhea
Diarrhea takes salt out with the water, which is why plain water isn't the best replacement. The World Health Organization's oral rehydration solution is clean water, salt and sugar. It's absorbed in the small intestine and replaces the water and electrolytes lost in stool. The solutions sold at drugstores work the same way.
- Drink at least 1 cup (240 mL) for every loose stool, as MedlinePlus advises, on top of what you'd normally drink.
- Skip caffeine, alcohol and carbonated drinks while it lasts.
- Leave out fruit juice and soda, which can make diarrhea worse.
For many people diarrhea is mild and goes away within a few days. MedlinePlus says to contact a provider if, in an adult, it isn't better in 5 days or gets worse; if there's blood or mucus in the stool; if a fever doesn't go away; if it comes with nausea or vomiting; or if stomach pain persists.
What IV fluids do once they are in a vein
The bag used for dehydration is usually an isotonic fluid such as 0.9% saline: salt water at about the body's own concentration. It does the same job an oral rehydration solution does, putting back water and salt. The difference is the route. An IV bypasses digestion entirely, which is why it matters when fluid won't stay down. It doesn't treat whatever caused the dehydration. MedlinePlus notes that a provider treating severe dehydration also treats the cause.
For children with stomach bugs, a Cochrane review of 17 trials found no clinically important difference between rehydrating by mouth and by IV, and about 1 in 25 children treated by mouth went on to need an IV. That review covered children only, and its authors conclude that drinking should come first for mild to moderate dehydration, with an IV if that fails.
What one liter of saline does
Water makes up about 60 percent of body weight, split between the inside of cells and the fluid around them. Saline spreads through that outside fluid, the blood plus the spaces between cells. A 2025 article in the British Journal of Surgery puts the share of an isotonic fluid like saline that stays in the blood vessels at about 20 percent, with the rest moving into the tissues. A liter is a real amount of fluid, and it's also a modest one next to the water the body already holds.
68% of a one-liter saline infusion had moved out of the bloodstream and into the tissues by the end of a one-hour drip. Measured in 10 healthy men, so a small study, but a clear picture of where a liter goes. Source: Lobo et al., Critical Care Medicine, 2010.
Can you just go get IV fluids?
Not on your own say-so, and not at home if you have severe dehydration or fluid that won't stay down. Those belong in a doctor's care or a hospital, where the cause gets looked at as well as the fluid.
At home, a clinician decides. At Las Vegas Mobile IV Therapy, every drip starts with a health check: vitals, your health history, the medicines you take and any allergies. The order for IV fluids comes from the team's ordering provider, Rich Majors, FNP-BC, a nurse practitioner with prescriptive authority, under medical oversight by the Medical Director, Dr. Daniel Olivero, MD. Licensed nurses and NREMTs give the drip at your home, hotel or office.
A home IV isn't for anyone with a sign from the right-away or 911 lists above, and that includes fluid that won't stay down. It's for someone with none of those signs who would rather have fluid given than drink it. It's a choice, not a faster cure. If that's you, the IV Fluids drip at home is 1000 ml of IV fluids over 35 minutes for $150, hydration only, with nothing added.
More questions about rehydrating
Are sports drinks good enough?
For mild dehydration from sweating, they can help, and the CDC says so. It also says they may not replace important nutrients and minerals. During a stomach bug, MedlinePlus suggests the electrolyte and fluid replacement solutions sold in drugstores instead, and the CDC calls those most helpful for mild dehydration.
Should I take salt tablets?
No. MedlinePlus says not to take salt tablets to treat dehydration, because they can cause serious complications. If you need salt back, an oral rehydration solution already contains it, and MedlinePlus suggests salty foods such as soup or pretzels once your stomach can handle food again.
When can I eat again?
Once the vomiting eases, try small amounts of food often instead of full meals. MedlinePlus suggests foods such as cereals, bread, potatoes, lean meats, plain yogurt, bananas, fresh apples and vegetables. MedlinePlus also says to keep drinking extra fluids between meals, even once you can eat.
How can I tell if a child is dehydrated?
The CDC says a dehydrated child may cry with few or no tears and be unusually sleepy or fussy, and MedlinePlus adds fewer wet diapers in babies. MedlinePlus says infants and young children are more likely to need IV fluids, so call your child's doctor rather than waiting it out.
Who should be more careful about dehydration?
MedlinePlus names older adults and people with conditions such as diabetes as being at higher risk, and medicines that make you urinate more, such as diuretics, add to the loss. If that's you or someone you care for, bring a provider in sooner. Don't stop a prescription medicine without asking first.
Sources
- MedlinePlus, National Library of Medicine. Dehydration.
- MedlinePlus, National Library of Medicine. Nausea and vomiting, adults.
- MedlinePlus, National Library of Medicine. Viral gastroenteritis (stomach flu).
- MedlinePlus, National Library of Medicine. When you have diarrhea.
- Centers for Disease Control and Prevention. About Norovirus.
- World Health Organization. Diarrhoeal disease (fact sheet).
- Hartling L, Bellemare S, et al. Oral versus intravenous rehydration for treating dehydration due to gastroenteritis in children. Cochrane Database of Systematic Reviews, 2006.
- Lobo DN, Stanga Z, et al. Effect of volume loading with 1 liter intravenous infusions of 0.9% saline, 4% succinylated gelatine and 6% hydroxyethyl starch on blood volume and endocrine responses. Critical Care Medicine, 2010.
- Ess M, Lobo DN. Ten steps towards better perioperative intravenous fluid therapy. British Journal of Surgery, 2025.
