Fatigue and increased thirst: what to know

Thirst often rises when the body loses water through sweating, vomiting, diarrhoea, fever or alcohol. Dehydration can cause tiredness, headache, dizziness, dry mouth and darker urine. Increased thirst that continues despite drinking may occur with high blood sugar, kidney problems, some medicines or a salt and water imbalance. Anaemia, coeliac disease, chronic fatigue syndrome and burnout can cause fatigue but do not explain every case of thirst. The timing of urination, appetite and weight change helps a clinician narrow the possibilities.

Drink regularly and choose water or an appropriate oral rehydration drink when fluid loss is evident. Avoid relying on alcohol or very sweet drinks to quench thirst. Note how much you drink, how often you urinate, urine colour, sweating, bowel symptoms, fever, medicines and whether thirst wakes you. Arrange a medical review if thirst persists, is accompanied by frequent urination or unexplained weight change, or leaves you unusually weak.

Seek emergency help for confusion, fainting, severe weakness, deep or rapid breathing, repeated vomiting, or inability to keep fluids down. Get prompt advice for very little urine, marked dizziness on standing, worsening drowsiness or symptoms after significant heat exposure. Do not delay assessment because drinking temporarily eases the thirst.

Could my medicines, recent illness, fluid loss or blood sugar explain this? Should my blood and urine be checked, and what should I monitor at home? How much fluid is appropriate if I have kidney or heart problems?