Less food, less water from food
Food normally provides around 20 to 30% of the water we take in each day (EFSA). Eat a lot less, and that share shrinks. Most people don’t drink more to make up for it.
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Hot topic. Cool heads.
GLP-1 medications and hydration: what you need to know.
On Wegovy, Ozempic or Mounjaro? Eating less changes more than your plate. Here’s what it can mean for your fluids, and the small habits that help.
Small sipsSteady habitsTalk to your prescriber
Little and often.
Small sips.
Steady days.
If you’re eating less, steady sipping through the day is often easier than big glasses at once. Keep a bottle in sight and make a glass part of moments you already have.
- Sip steadily from morning to evening
- Between meals if you’re feeling sick
- The NHS suggests 6 to 8 glasses a day
01 · The odd flat feeling
Why hydration deserves a little more thought.
If you’re on a GLP-1 medication, you might have noticed days that feel a bit flat. Tired for no obvious reason. A headache that turns up out of nowhere, even when nothing strenuous has happened.
There can be lots of reasons, and the NHS lists feeling tired among the common side effects of semaglutide and tirzepatide. But feeling tired, headachy and light-headed are also classic signs of not drinking enough. When you’re eating a lot less, it’s easier than you’d think to fall short on fluids without noticing.
So it’s worth keeping an eye on what you drink, and talking to your prescriber or pharmacist about anything that doesn’t go away. Here’s what’s going on, and what tends to help.
02 · What changes
How GLP-1 medications
can change the picture.
These medicines work by slowing how quickly your stomach empties and turning down your appetite. That’s the point. It also changes where your fluids and minerals come from.
Feeling or being sick
The NHS lists nausea, vomiting and diarrhoea among the common side effects. Being sick or having diarrhoea means losing fluid and the salts that go with it.
Fewer minerals from your plate
Most of the sodium, potassium and magnesium we get comes from food. Smaller meals can mean less of each, which is why a varied diet still matters when portions shrink.
Interactive · Where your water comes from
Eat less, and the gap shows up in your glass.
An illustration, not a target. EFSA’s adequate total water intake is 2.0 litres a day for women and 2.5 litres for men, from food and drinks together, with food giving around 20 to 30% of it. We’ve used 25%. Your needs may differ, so ask your prescriber or pharmacist.
03 · Water first
Where electrolytes fit in.
- Water is the best everyday choice
- Electrolytes help your body manage its fluid balance
- If you’ve been sick, a pharmacist can help
When most people think about staying hydrated, they think: drink more water. That’s right, and water is still the best everyday choice. Tea, coffee and lower-sugar drinks count too.
Electrolytes are minerals, like sodium, potassium and magnesium, that carry a small electrical charge in the body and help it manage its fluid balance. Most of them come from food, so when you’re eating a lot less, it’s worth thinking about where yours come from.
Being sick or got diarrhoea?
The NHS says that if you’re losing a lot of fluid this way, you need to put back the sugar, salts and minerals your body has lost, and a pharmacist can recommend an oral rehydration solution. That’s the right product for the job. Spruce isn’t a rehydration solution.
On ordinary days, an everyday electrolyte drink is simply one way to add a few minerals to a glass of water. Spruce daily electrolytes have four (sodium, potassium, magnesium and calcium), low sodium and no sugar. The magnesium in each sachet contributes to electrolyte balance.
04 · The quiet one
Magnesium: worth knowing about.
Of all the minerals, magnesium is probably the most overlooked. You’ll find it in foods like spinach, nuts and wholemeal bread, and the NHS says you should be able to get all you need from a varied, balanced diet. When portions get much smaller, it’s worth checking your diet still covers it.
Magnesium contributes to:
- the reduction of tiredness and fatigue
- normal muscle function
- normal psychological function
- electrolyte balance
- normal energy-yielding metabolism
Spruce Wind-down is a peach drink with 250mg of magnesium (66% of your daily reference intake) from a blend of marine magnesium and magnesium glycinate, plus vitamin B6 and zinc. You mix one sachet into cold water.
Two things to know.
The NHS says having 400mg or less a day of magnesium from supplements is unlikely to cause any harm, and that high doses (more than 400mg) can cause diarrhoea. Always tell your prescriber or pharmacist about any supplements you take.
05 · Practical habits
Small sips.
Steady days.
Big dramatic changes rarely stick. Small, consistent habits do. Tick what applies and we’ll lay out a simple day.
Your guide6–8glasses of fluid a day (NHS)
- Sip steadily. These medicines slow how fast your stomach empties, so big drinks in one go can feel uncomfortable. Little and often is easier.
- Make it visible. A marked bottle or a reminder on your phone helps the sips add up.
- Start the day with a glass. Before coffee, if you can.
General habits, not treatment. The NHS suggests 6 to 8 glasses of fluid a day, more if you’re being sick, have diarrhoea, it’s hot or you’re active. If you feel sick, the NHS suggests starting with small sips.
06 · Know the signs
Could you be dehydrated?
Tick anything you’ve noticed today. This uses the NHS list of dehydration signs and tells you what the NHS suggests. Nothing is saved or sent.
07 · Where Spruce fits
Making hydration
genuinely easy.
We built Spruce to make drinking enough feel effortless. No faff, no complicated routine. Spruce isn’t a treatment and isn’t designed for use with any medicine. If you take prescription medication, check with your prescriber or pharmacist before adding a supplement.
Daily electrolytes
Lemon & Pomegranate or Cherry & Lime. Four electrolytes, low sodium, no sugar. Magnesium contributes to electrolyte balance.
Wind-down
Peach magnesium: 250mg from a marine and glycinate blend, with B6 and zinc. Magnesium and vitamin B6 contribute to the reduction of tiredness and fatigue.
Water enhancers
If plain water is the hard part, a sugar-free fruit sachet can make it something you want to drink. Vitamin D + C, Focus, Glow and Revive.
92% of customers say they drink more water with Spruce*
Spruce products are food supplements. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. They are not intended to diagnose, treat, cure or prevent any disease. If you are taking prescription medication, speak to your prescriber or pharmacist before adding any new supplement to your routine.
Less wondering. More water.
GLP-1 and hydration,
answered.
Short answers. For anything about your treatment, ask your prescriber or pharmacist.
Can GLP-1 medications make you dehydrated?
They can make it easier to fall short. You get less water from food when you eat less, and the NHS lists nausea, vomiting and diarrhoea among the common side effects, which all lose fluid. Keep sipping through the day and speak to your prescriber or pharmacist about side effects that bother you or don’t go away.
How much should I drink on Wegovy, Ozempic or Mounjaro?
The NHS’s general guide is 6 to 8 glasses of fluid a day, more if you’re being sick, have diarrhoea, it’s hot or you’re active. Your prescriber or pharmacist can advise on what’s right for you.
Do I need electrolytes on a GLP-1 medication?
Not necessarily. Water is the best everyday choice and most minerals come from food. If you’re being sick or have diarrhoea, the NHS says a pharmacist can recommend an oral rehydration solution. An everyday electrolyte drink is just one way to add a few minerals to your water on ordinary days.
Is Spruce a treatment for GLP-1 side effects?
No. Spruce is a range of food supplements for everyday hydration. It isn’t a treatment for anything and isn’t designed to be used with any medicine. Speak to your prescriber or pharmacist about side effects.
Can I take magnesium with semaglutide or tirzepatide?
Ask your prescriber or pharmacist before adding any supplement. The NHS says up to 400mg a day of magnesium from supplements is unlikely to cause harm, and that high doses can cause diarrhoea. Wind-down has 250mg per sachet.
Why do I feel tired on a GLP-1 medication?
The NHS lists feeling tired as a common side effect, and tiredness is also a sign of dehydration. If it bothers you or doesn’t go away, speak to your prescriber or pharmacist.
When should I get help?
The NHS says to ask for an urgent GP appointment or contact NHS 111 if you have signs of serious dehydration, such as feeling unusually tired, dizziness that doesn’t go away when you stand, or peeing less than normal. Call NHS 111 if you think you’re having serious side effects from your medicine.
Sources:
NHS: semaglutide ↗
NHS: tirzepatide ↗
NHS: dehydration ↗
NHS: water, drinks and your health ↗
NHS: magnesium and other minerals ↗
EFSA (2010): dietary reference values for water ↗
GB nutrition and health claims register ↗
*Spruce customer survey, as published on spruce-water.com. Reviewed 21 October 2026 by the Spruce team. General information, not medical advice.