Why do I get night sweats? Menopause and medication lead; fever is the flag

If you are a woman in midlife, the overwhelming reason you wake up drenched is the menopause transition, in which hot flushes and night sweats — the same event, one felt by day and one by night — last a median of 7.4 years [s1]. In older adults of either sex, night sweats are common and usually benign; about one in ten primary-care patients over 64 are bothered by them [s2], and a large follow-up study found that reporting them did not predict dying sooner [s3]. The pattern that does warrant attention is night sweats alongside fever or unexplained weight loss [s2].

That ordering matters, because night sweats are a symptom the internet is quick to escalate straight to cancer, when the evidence puts the frightening explanations last, not first.

The menopause answer, with real numbers

The best data on how long menopausal sweats last comes from the Study of Women's Health Across the Nation (SWAN), which followed 3,302 women, 1,449 of them with frequent vasomotor symptoms, across the menopause transition [s1]. The median total duration of frequent symptoms was 7.4 years, and they persisted a median of 4.5 years after the final menstrual period [s1]. Duration varied sharply with when symptoms began and with ethnicity: women who were still premenopausal or early in the transition when frequent symptoms started had the longest course, a median above 11.8 years, while those whose symptoms began only after the final period had the shortest, a median of 3.4 years [s1]. African American women reported the longest duration of any group, a median of 10.1 years [s1]. The same analysis linked a longer course to being younger at onset, to lower educational level, and to greater perceived stress, symptom sensitivity, and depressive and anxiety symptoms when the sweats first appeared — a reminder that how long they last is shaped by more than hormones alone [s1]. This is far longer than the "a year or two" many women are told to expect, and it is the context for our coverage of non-vasomotor menopause symptoms and of what actually helps hot flushes.

Common in later life — and usually not ominous

Night sweats are not only a menopausal phenomenon. In a cross-sectional study of 795 primary-care patients older than 64, 10% were bothered by night sweats, 9% by day sweats and 8% by hot flushes, with 18% reporting at least one [s2]. The reassuring counterpart came from the same research group, which tracked two cohorts of people over 65 (682 and 852 patients) for an average of 7.3 and 7.5 years: those who reported night sweats were no more likely to die, or to die sooner, than those who did not, and that held even for more severe night sweats [s3]. In most cases, the authors note, the cause is simply never identified [s3]. A hot bedroom, alcohol, anxiety and disrupted sleep account for a great many; why waking in the night is itself so normal is covered separately.

The medicines that cause it

A frequently missed cause is prescription drugs. Analysing 413 primary-care patients aged 65 to 94, of whom 9.2% reported at least moderate night sweats, researchers found only three drug classes independently associated with the symptom after adjustment: selective serotonin reuptake inhibitors (SSRIs), the widely used antidepressants (odds ratio 3.01; 95% CI 1.26 to 7.19); angiotensin receptor blockers taken for blood pressure (OR 3.44; 95% CI 1.36 to 8.69); and thyroid hormone supplements (OR 2.53; 95% CI 1.24 to 5.15) [s4]. Age, sex, body-mass index and the sheer number of medicines taken were not associated [s4]. It is a small study and shows association rather than proof, but it points to a check worth making before assuming something worse: the sweats may have started with a pill.

The flag that changes the picture

The one clear alarm signal in the primary-care data is fever. In the same older cohort, night sweats were strongly associated with fever, at an odds ratio of 12.60 (95% CI 6.58 to 24.14) — far larger than any other association measured [s2]. Drenching night sweats that come with fevers, with unexplained weight loss, or that are new and persistent, are the ones that need a clinician's assessment, because that combination is where the uncommon serious causes — including chronic infection and some cancers — concentrate. The point is not that night sweats are usually dangerous; the evidence says they usually are not [s3]. It is that a specific cluster of accompanying symptoms is what separates a nuisance from a warning. This article is informational and is not medical advice, and does not recommend starting, stopping or changing any medication.

Sources

• Duration of Menopausal Vasomotor Symptoms Over the Menopause Transition — JAMA Internal Medicine, 2015-02-16
• Prevalence and predictors of night sweats, day sweats, and hot flashes in older primary care patients — Annals of Family Medicine, 2004-10-05
• The Prognostic Implications of Night Sweats in Two Cohorts of Older Patients — Journal of the American Board of Family Medicine, 2010-01-05
• Selective Serotonin Reuptake Inhibitors and Night Sweats in a Primary Care Population — Drugs - Real World Outcomes, 2015-02-06