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Why water gets forgotten on a GLP-1

Much of our daily fluid normally arrives with food and with the drinks that go with meals. When a GLP-1 shrinks meals, that fluid shrinks too. Many people also notice they simply do not feel thirsty, in the same way they no longer feel hungry.

Then there are the side effects. Nausea makes drinking unappealing, and vomiting or diarrhoea, which are most common in the days after a dose and after a step up, can lose a lot of fluid quickly. The Mounjaro, Wegovy and Ozempic patient leaflets all mention dehydration, and warn that it can lead to kidney problems in some people.

Signs you are not drinking enough

• Dark yellow or strong-smelling urine, or not needing the toilet much
• Headaches, especially later in the day
• Feeling dizzy or light-headed when you stand up
• Constipation that is worse than usual
• Tiredness that does not match your sleep

If you cannot keep fluids down, or you feel very unwell, contact your prescriber, a pharmacist or NHS 111 rather than waiting it out.

How much to drink

For most adults the NHS guide is 6 to 8 glasses a day, roughly 1.5 to 2 litres, with more when it is hot, when you exercise, or when you have been sick. Water, milk, sugar-free squash, tea and coffee all count. Some people are told to limit fluid for heart or kidney reasons, so follow any personal advice you have been given.

Pale straw-coloured urine is a practical everyday check.

What about electrolytes?

When you are eating much less, or losing fluid through vomiting or diarrhoea, you also lose salts such as sodium and potassium. Oral rehydration sachets from a pharmacy are designed for exactly this after a bout of sickness. Some people use electrolyte tablets in hot weather or after exercise. If you have high blood pressure, heart or kidney problems, ask before adding salts.

Habits that make it easier

• Front-load the day. A large glass on waking and one mid-morning gets a third of the target done before appetite matters.
• Sip, do not gulp. Small, frequent amounts are easier on a queasy stomach than a pint at once.
• Tie it to things you already do. A glass with each medication, each coffee, each trip to the kitchen.
• Plan for dose day. If the first day or two after your jab or shot are your roughest, keep water and a rehydration sachet nearby before you inject.
• Count, briefly. Most people who think they drink "plenty" find it is closer to four glasses once they actually count.

How PepLevel handles it

Water in PepLevel is one tap. The Water tile on Today logs a glass the moment you touch it. There is nothing to open and nothing to confirm, because a habit that takes more than a second does not survive a busy week. The tile shows today's total against a goal if you have set one (in millilitres, or fluid ounces in the US), and the full Water & Electrolytes sheet lets you log other amounts or undo a mistake.

If it helps, add a water check-in at whatever time suits you. It arrives with a Log a glass button right on the notification, so logging takes one tap without opening the app. With Apple Health sync on, water is also written to Health so it counts wherever else you look.

Side effects live in the same app. If the days you logged nausea or diarrhoea are also the days your water total was lowest, you will see it, and so will your prescriber if you share the appointment summary.

Common questions

Does Mounjaro make you dehydrated?

It can contribute. Tirzepatide and other GLP-1s often reduce thirst and meal size, and side effects like vomiting or diarrhoea lose fluid. The patient leaflet warns that dehydration can cause kidney problems, so drinking regularly matters.

How much water should I drink on Wegovy?

There is no Wegovy-specific amount. The NHS suggests 6 to 8 glasses of fluid a day for most adults, and more in hot weather, with exercise or when you have been sick. Follow any personal limits your doctor has given you.

Can I drink electrolytes on a GLP-1?

Many people use oral rehydration sachets after vomiting or diarrhoea, which is what they are made for. If you have high blood pressure, heart or kidney problems, check with your prescriber or pharmacist before adding salts regularly.

Water in one tap

Log a glass from Today or straight from a check-in notification. Coming soon to the App Store.

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