Staying Hydrated on a GLP-1: Why It Matters More Than You Think

Water rarely gets the credit it deserves. On a GLP-1 medicine it matters even more than usual, and getting it right can make the early weeks a good deal more comfortable.

Here is why, how much to aim for, and how to actually drink enough when your appetite, and your sense of thirst, have both gone quiet.

Why hydration matters more on a GLP-1

Two things happen on these medicines that make dehydration easy to slip into.

First, you eat less. A surprising amount of our daily fluid actually comes from food, so smaller meals mean less fluid without you noticing.

Second, the common early side effects, things like nausea, constipation and tiredness, are all made worse by being even slightly dehydrated. Staying on top of your fluids is one of the simplest ways to take the edge off them.

There is also reasonable evidence that a glass of water before a meal helps you feel fuller, which works nicely alongside how the medicine already behaves.

How much should you drink?

The NHS suggests 6 to 8 glasses a day, which is around 1.2 litres, as a general guide for most people.

If you would like a figure tailored to you, a common rule of thumb is 30 to 35ml per kilogram of body weight. For someone who weighs 75kg that comes to roughly 2.5 litres a day. You will need more if you exercise, if the weather is hot, or if you are dealing with GLP-1 side effects.

If the maths feels fiddly, just aim for 8 glasses a day to begin with and adjust based on how you feel and the colour of your urine.

How to tell if you are not drinking enough

Your body gives you fairly clear signals. Watch for:

Urine that is dark yellow rather than pale
Headaches or trouble concentrating
A dry mouth or lips
Feeling tired even after a good night's sleep
Feeling dizzy when you stand up
Constipation
Hunger or cravings that do not quite add up

Pale yellow is the colour you are aiming for. If you notice several of these signs, it is usually your cue to drink a bit more, a bit more often.

Simple ways to drink more

The trick is not willpower. It is making water the easy option.

Start the day with a glass before your tea or coffee.
Keep a bottle where you can see it. Out of sight really does mean out of mind.
Have a glass 20 to 30 minutes before meals.
Attach it to things you already do, like a few sips after every bathroom break or when you sit down at your desk.
If plain water bores you, add lemon, cucumber, mint or a few berries.
Track it for a week or two until the habit sticks.

A rough plan for the day

If you like a bit of structure, something like this gets most people to around 2.5 litres:

On waking: two glasses to rehydrate after sleep
Through the morning: two glasses, sipped slowly
Before lunch: one glass
Afternoon: two glasses to head off the energy dip
Early evening: two glasses, finishing a couple of hours before bed

A few things to watch

Waiting until you feel thirsty means you are already behind, so sip steadily rather than trying to catch up in one go. Your body can only absorb so much at once, and a litre in one sitting mostly ends up in the bathroom.

Tea and coffee do count towards your fluids, but plain water is still the best choice, and caffeine has a mild drying effect. Alcohol is the exception. It actively dehydrates you, so it does not count.

And try to ease off the fluids a couple of hours before bed, so you are not up in the night.

It is the least glamorous habit on the list, and probably the best value for the effort. A full glass is a good place to start right now.

Sources: NHS (Water, drinks and hydration) and the British Nutrition Foundation.