Several widely used medications can raise blood sodium levels above the normal threshold of 145 mEq/L, a condition called hypernatremia. They do this through two main routes: causing your body to lose more water than sodium, or directly adding sodium to your system. Lithium is the most frequently reported culprit, but the full list spans mood stabilizers, diuretics, antifungals, laxatives, steroids, and even certain IV antibiotics.
Lithium: The Most Common Cause
Lithium, prescribed for bipolar disorder, is the single most reported medication behind drug-induced high sodium. It interferes with the kidney’s collecting tubes, the part of the kidney responsible for reabsorbing water back into the body. Normally, antidiuretic hormone (ADH) signals these tubes to hold onto water. Lithium blocks that signal and also reduces the production of water channels in kidney cells called aquaporin-2. The result is that your kidneys produce large volumes of dilute urine, pulling water out of the body while sodium stays behind and becomes more concentrated in the blood.
This condition, called nephrogenic diabetes insipidus, can develop at any point during lithium therapy. The excessive urination and thirst are often the first signs. The water channel changes are generally reversible once lithium is stopped, but in long-term users, some degree of kidney concentrating defect can persist. Patients on lithium who develop diabetes insipidus typically need twice-daily monitoring of electrolytes because the risk of hypernatremia climbs significantly.
Medications That Cause Water Loss Through the Kidneys
Beyond lithium, a range of drugs push sodium levels up by making the kidneys excrete too much water relative to sodium. They do this through several distinct mechanisms.
Drugs That Impair the Kidney’s Response to ADH
These medications create a situation similar to lithium, where the kidneys stop responding properly to the hormone that tells them to conserve water:
- Amphotericin B, an antifungal used for serious infections, caused hypernatremia in about 15% of patients in one study of the liposomal form.
- Demeclocycline, a tetracycline antibiotic, can cause this water-wasting effect in nearly all patients at higher doses.
- Foscarnet, an antiviral, has been linked to high sodium at high doses.
- Colchicine, used for gout, has been reported to push sodium as high as 160 mEq/L after large dose ingestion.
- Vinblastine, a chemotherapy drug.
Some of these drugs don’t directly block ADH but instead cause low potassium or high calcium levels, which in turn impair the kidney’s ability to concentrate urine. Cisplatin (a chemotherapy agent), aminoglycosides (a class of antibiotics), and high doses of vitamin A or D can all trigger hypernatremia through this indirect path.
Drugs That Reduce ADH Production
Phenytoin, an anti-seizure medication, temporarily suppresses ADH release from the brain, leading to increased water loss. Alcohol does the same thing, which is one reason heavy drinking leads to dehydration that goes beyond simple fluid loss.
Loop Diuretics and Osmotic Agents
Loop diuretics like furosemide are designed to make the kidneys excrete more fluid. While they remove sodium too, the net effect can tip toward water loss and rising sodium levels, especially in patients who aren’t replacing fluids adequately.
Mannitol, given intravenously to reduce brain swelling, works by creating an osmotic pull that draws water into the urine. It’s a significant contributor to high sodium in hospitalized patients, accounting for 7% to 21% of in-hospital hypernatremia cases depending on the study. The mechanism is straightforward: mannitol stays in the kidney tubules and drags water along with it, but sodium doesn’t follow at the same rate. The urine volume goes up dramatically while the blood becomes more concentrated.
Medications That Cause Water Loss Through the Gut
Lactulose, commonly prescribed for constipation and liver-related brain fog (hepatic encephalopathy), is an osmotic laxative that pulls water into the intestines to soften stool. That water loss can outpace sodium loss, concentrating what remains in the blood. In one study, sodium levels exceeded 145 mEq/L during 20 out of 75 courses of lactulose treatment, making this a surprisingly common side effect. Sorbitol, another osmotic laxative, carries the same risk.
Vasopressin Receptor Blockers
Tolvaptan and related drugs are specifically designed to block the receptor that ADH uses to tell the kidneys to retain water. They’re prescribed for conditions involving excess water retention, like certain types of heart failure or a syndrome that causes abnormally low sodium. The irony is that by doing their job too well, they can overcorrect and push sodium too high. In clinical trials, hypernatremia occurred in about 1.8% of patients on tolvaptan.
Corticosteroids and Sodium Retention
Steroids like prednisone raise sodium through a different mechanism than most drugs on this list. Rather than causing water loss, they promote sodium retention. Glucocorticoids can bind to the same receptors in the kidney that aldosterone uses, the hormone primarily responsible for telling the kidneys to reabsorb sodium. They also stimulate sodium transport processes that are normally controlled by the renin-angiotensin-aldosterone system. Additionally, corticosteroids increase the body’s production of urea, which can act as an osmotic agent in the kidneys and contribute to water loss.
The sodium-retaining effect is most pronounced with steroids that have stronger mineralocorticoid activity, such as fludrocortisone and hydrocortisone, but even “purer” glucocorticoids like prednisone and dexamethasone can shift sodium balance.
IV Medications With Hidden Sodium
Some medications raise sodium levels simply because they contain a lot of sodium in their formulation. This is especially relevant for hospitalized patients receiving IV drugs. Vancomycin, one of the most commonly used IV antibiotics, contains about 708 mg of sodium per standard dose. Meropenem delivers around 290 mg, and piperacillin-tazobactam contributes 195 to 260 mg per dose. When patients receive multiple doses daily along with IV fluids that also contain sodium, the total load adds up quickly.
Hypertonic sodium bicarbonate, used to treat certain overdoses and severe acidosis, directly infuses concentrated sodium into the bloodstream. Hypertonic saline solutions used for various medical procedures carry the same risk.
NSAIDs: A More Complex Picture
Non-steroidal anti-inflammatory drugs like ibuprofen and naproxen cause sodium retention by blocking prostaglandins in the kidneys. Prostaglandins normally inhibit sodium reabsorption in the kidney tubules, so when NSAIDs suppress them, the kidneys hold onto more sodium and water. This leads to weight gain, swelling, and elevated blood pressure in some people. However, NSAIDs more commonly cause low sodium (hyponatremia) rather than high sodium, because the water retention tends to dilute sodium concentrations. The sodium-retaining effect is most clinically relevant when it worsens fluid overload in people with heart failure or interferes with blood pressure medications.
Symptoms to Watch For
High sodium primarily affects the brain. When sodium rises gradually, symptoms can be subtle or absent. When it rises quickly or exceeds about 160 mEq/L, neurological symptoms become more apparent. These include intense thirst, confusion, irritability, muscle twitching, and in severe cases, seizures or reduced consciousness. Because the brain is sensitive to shifts in water balance, cells in the brain shrink as water moves out to compensate for the concentrated blood, which is what drives these symptoms.
If you’re taking any of the medications listed above and notice persistent excessive thirst, unusually high urine output, or any new confusion or mental fogginess, those warrant a blood test to check sodium levels. The risk is highest in people who can’t freely access water on their own, such as older adults with limited mobility, hospitalized patients, or anyone with impaired thirst sensation.