A 35-year-old woman with schizophrenia is brought to the ED from her board and care for worsening confusion, behavioral changes, and loose, hard-to-follow speech. Staff worry she is psychiatrically decompensating. When asked about changes in her routine, they mention that she has been using the bathroom much more often. Before routine labs return, she has a seizure and is transferred to medicine. Her sodium is 115 mEq/L.

Psychogenic or primary polydipsia (PP) can hide in plain sight on psychiatric units. New confusion, agitation, or disorganization may be mistaken for psychiatric decompensation. Unless you’re vigilant, it’s easy to miss clues, such as repeated trips to the water fountain, frequent bathroom use, or carrying water everywhere. When water intake overwhelms the kidneys’ ability to excrete free water, severe hyponatremia can develop, leading to cerebral edema, seizures, delirium, coma, and, in rare cases, death.

Who gets PP?

The exact prevalence of PP is unknown, but estimates among psychiatric patients range from 3% to 25% (Iftene F et al, Psychiatry Res 2013;210(3):679–683). PP is strongly associated with schizophrenia, especially in chronically ill or institutionalized patients, but it also occurs in mood disorders, anxiety disorders, OCD, and intellectual disability.

The cause appears to be multifactorial. Anticholinergic dry mouth may contribute but does not fully explain the syndrome. Dopaminergic and opioid pathways may play a role, and some patients describe drinking as compulsive, soothing, or driven by hallucinations or delusional beliefs (Rizvi S et al, Cureus 2019;11(8):e5320). Risk factors include chronic psychosis, institutionalization, negative symptoms, smoking, male sex, and a history of polydipsia or hyponatremia.

Recognizing PP

Patients with PP usually present with polydipsia and polyuria. Mild to moderate hyponatremia (sodium 125–134 mEq/L) may cause vague symptoms such as dizziness, nausea, vomiting, headache, weakness, or malaise. Severe hyponatremia, typically below 125 mEq/L, can cause confusion, agitation, dysarthria, delirium, seizures, obtundation, or coma.

Do not rely only on the patient’s report. Many patients won’t volunteer how much they are drinking and may drink surreptitiously. Ask staff and family specific questions:

• Is the patient constantly asking for water?
• Are they carrying cups, pitchers, or bottles?
• Are they making frequent bathroom trips?
• Have they been drinking from sinks, showers, or toilets?
• Has there been rapid weight gain over hours or days?
• Have there been new falls, vomiting, confusion, or seizures?

The usual lab pattern in PP is low serum sodium with very dilute urine: low urine osmolality and low urine sodium. The differential includes diabetes mellitus, diabetes insipidus, and syndrome of inappropriate antidiuretic hormone (SIADH) (for more on differentiating polyuria and hyponatremia, see: www.thecarlatreport.com/polyuria-hyponatremia).

SIADH warrants special attention because it can coexist with PP and many psychiatric medications can contribute to it, including SSRIs, SNRIs, antipsychotics, carbamazepine, oxcarbazepine, valproic acid, and rarely topiramate (Pinkhasov A et al, J Psychosom Res 2021;151:110654). Elevated urine sodium and concentrated urine point to SIADH, while low urine sodium and very dilute urine favor PP.

Acute management on the unit

Mild hyponatremia

For patients who are asymptomatic or mildly symptomatic:

• Restrict fluids: Limit intake to 1.5 liters per day, depending on severity.
• Add supervision if needed: Initiate 1:1 nursing or staff observation to monitor intake and reduce surreptitious drinking.
• Remove access points: Take cups, pitchers, and containers out of the room, and prevent patients from bringing containers into the bathroom. Door-ajar bathroom use may be necessary if you suspect sink or toilet drinking; preserve privacy as much as safety allows.
• Check labs daily: Monitor electrolytes daily in patients with suspected or confirmed PP and hyponatremia.
• Escalate if refractory: If hyponatremia doesn’t respond to fluid restriction, consult medicine or nephrology and consider salt tablets (typically 1–3 g daily) until sodium normalizes.

Patients may become distressed, argumentative, or disruptive when fluid access is limited. Explain the rationale clearly, keep a calm and consistent team approach, and avoid framing restriction as punishment.

Severe hyponatremia

Severe or symptomatic hyponatremia is a medical emergency. Transfer to a medical setting if the patient has any of the following:

• Seizure, delirium, obtundation, or focal neurologic symptoms
• A sodium below 125 mEq/L with concerning symptoms

The psychiatrist’s role is to recognize the emergency, stop potential offending medications when appropriate, and alert the medical team to the patient’s water-intake history. Hypertonic saline may be indicated, but severe hyponatremia requires medical or nephrology oversight. The goal is to reduce acute neurologic danger while avoiding overly rapid correction, which can cause osmotic demyelination syndrome, a rare but serious complication of rapid sodium shifts (Adrogué HJ et al, N Engl J Med 2000;342(21):1581–1589). Once the patient returns to psychiatry, keep polydipsia on the active problem list so staff continue monitoring the patient’s fluid intake, weights, and sodium.

Review the medication list

Medication review is one of the psychiatrist’s most important contributions. Ask two questions:

1. Is anything increasing thirst or dry mouth?
2. Is anything increasing the risk of hyponatremia?

Anticholinergic burden may not cause PP, but dry mouth can increase the drive to drink. Reduce anticholinergic medications when possible. For a patient taking a strongly anticholinergic antipsychotic, switching to a lower-anticholinergic alternative may help, especially when the current medication causes dry mouth or other adverse effects.

Also review medications associated with SIADH or hyponatremia, including SSRIs, SNRIs, carbamazepine, oxcarbazepine, and valproate. Diuretics, particularly thiazides, also increase the risk of hyponatremia. Avoid starting these medications unless clearly indicated, monitor sodium closely when they are necessary, and consider switching to lower-risk alternatives if hyponatremia is present or recurrent.

Lithium requires separate consideration. Include lithium-induced nephrogenic diabetes insipidus in the differential, particularly if the patient has polyuria with persistently dilute urine and a normal or elevated serum sodium. A normal serum sodium does not exclude nephrogenic diabetes insipidus because a patient with intact thirst and unrestricted access to water may drink enough to replace the urinary water losses.

Pharmacologic options for recurrent PP

Evidence for medication treatment of PP is limited. Most studies are small, nonrandomized, or based on case reports or case series. The sole RCT, on haloperidol versus olanzapine, did not show clear benefit (Goldman MB and Hussain N, J Clin Psychopharmacol 2004;24(6):678–680).

Evidence by agent:

• Clozapine: Strongest signal for recurrent or severe PP. Reported to improve PP and hyponatremia in one study and two case series (Kirino S et al, Prog Neuropsychopharmacol Biol Psychiatry 2020;96:109756). Associated with lower prevalence of hyponatremia compared with first-generation and other second-generation antipsychotics (Serrano A et al, Aust N Z J Psychiatry 2014;48(2):183–192). Not every patient with PP needs clozapine, but it deserves consideration in patients with schizophrenia and recurrent PP, repeated hyponatremia, or persistent psychotic symptoms driving water intake.
• Acetazolamide and propranolol: Evidence is thin but promising (Havens TH et al, J Psychosom Res 2022;152:110674).
• Naloxone, naltrexone, clonidine, ACE inhibitors, angiotensin receptor blockers, and demeclocycline (an older tetracycline antibiotic sometimes used for SIADH): Evidence is mixed or negative.

Preventing recurrence

For patients with a history of PP, regular monitoring can detect recurrence early. Weigh patients daily, ideally at the same time each morning; in higher-risk patients, add an afternoon weight. Small fluctuations are expected, but rapid daytime weight gain (eg, 1–2 kg) should prompt reassessment of fluid intake and serum sodium (Vieweg WV et al, Psychiatry Research 1988;26(3):305–312). Also, monitor serum electrolytes regularly. Weekly checks are reasonable for many higher-risk inpatients. At discharge, communicate the need for ongoing laboratory monitoring to outpatient providers.

Behavioral interventions can help. In reinforcement programs, patients earn tokens for staying within a prescribed fluid limit and cooperating with daily weights or sodium monitoring. Group therapy or CBT to address thoughts or urges that drive compulsive drinking may benefit patients in long-term residential or forensic facilities. Encourage smoking cessation to eliminate an unnecessary risk factor for PP.

The patient is admitted to the medical unit and receives supervised correction with hypertonic saline. Once stable, she returns to the inpatient psychiatric unit. She had been taking chlorpromazine and lithium before admission; given chlorpromazine’s anticholinergic burden and lithium’s potential to complicate water balance, you do not restart them. You begin risperidone to target her psychosis and monitor daily weights and weekly sodium levels. She recalls hearing voices telling her to drink water, which do not recur on the new regimen. At discharge, board and care staff are instructed to watch for excessive drinking, frequent bathroom use, or acute mental status changes. Her outpatient psychiatrist will monitor sodium monthly.

CARLAT VERDICT: PP is easy to miss because hyponatremia can resemble worsening psychosis, agitation, or delirium. In psychiatric patients, especially those with schizophrenia, abrupt mental status changes or signs of excessive or surreptitious water intake warrant a sodium check. Manage mild cases with fluid restriction, observation, daily weight checks, and electrolyte monitoring. Severe or symptomatic hyponatremia belongs on a medical service with nephrology input. Once the crisis passes, reduce medications that worsen thirst or hyponatremia, consider clozapine for recurrent cases, and give outpatient clinicians and residential staff clear triggers for repeat sodium checks.