Side effects on oral semaglutide: what to expect, and what actually helps

Starting a new medicine means starting with a lot of unknowns. How will it feel? What's normal? When should you worry?

If you're thinking about starting oral semaglutide if and when it comes to the UK, the most useful thing for you to know is that side effects are common, they're usually manageable, and they tend to ease as your body adjusts. For some people, the first few weeks can be genuinely uncomfortable. But most patients find their feet, and the trial data backs that up.

This guide isn't a replacement for the patient information leaflet that comes with your medicine - that remains the source of truth. 

A note before we go further: oral semaglutide isn't yet licensed in the UK for weight loss. Numan will only make it available once MHRA approval is in place. The information below is based on the licensed US version and may be subject to change.

Why side effects happen in the first place

GLP-1 (the hormone semaglutide mimics) has receptors all over your body, including the gut and the brain. When you start taking semaglutide, those receptors switch on at once. Your stomach starts emptying more slowly, your appetite signals get rewired, and your digestive system begins working in a rhythm it isn't used to.¹

That shift is what makes the medicine work. It's also what makes you feel a bit off in the first few weeks. 

Dose increases (called titration) are the windows where side effects are most likely to flare up. Each time you step up, your body has a few weeks of recalibrating to do. By the time you've been on a steady dose for a month or so, most people find that the side effects have settled compared to when they first started.

What's most likely to happen, and what helps

Nausea

The most common side effect, by some distance. It usually peaks in the first week or two after starting, and again briefly after each dose increase. For most people it eases on its own as your body adjusts.¹

What helps:

• Eat slowly: The faster you eat, the more you overshoot the new "I'm full" signal.

• Smaller portions, more often: Three big meals can feel like too much. Four or five smaller ones tend to sit better.

• Avoid heavy, fatty, fried, or very spicy food: Bland low-fat options like toast, plain rice, crackers, soups, and broths are easier going.

• Don't lie down: Stay upright for at least 30 minutes after eating.

• Stay on top of hydration: Sips throughout the day rather than big gulps in one go.

• Try ginger or peppermint tea: Small things that take the edge off.

Constipation

Slower digestion means slower bowel movements for some people. Increase fibre gradually, as sudden changes can backfire, and drink more water than you think you need. A short daily walk helps more than people often expect. If you haven't opened your bowels for three days or longer, message us.

Diarrhoea

Less common than constipation, but it does happen. Sip fluids, stick to plain foods, and rest. If it isn't settling within a few days, get in touch.

Vomiting

Worth flagging on its own. With oral semaglutide, vomiting is slightly more common than with the injectable form, with around 3 in 10 patients in the OASIS 4 trial having reported it, compared with about 1 in 4 on the injection.¹ It's linked to how the medicine is absorbed through the stomach.

Tiredness

Some people feel a dip in energy in the first few weeks.¹ It's a combination of your body adjusting to the medicine, eating less, and, for some, losing weight more quickly than they're used to.² Eating regularly (even if portions are smaller), prioritising protein, and drinking more water than feels normal all help. If fatigue is sticking around, your health coach can help unpick what's going on.

A note from a health coach

The first few weeks on this medicine can feel disorientating. You're eating less, feeling full faster, and your body's resetting how it manages hunger. That's a lot at once.

Two things tend to help most:

1. Don't skip meals just because you're not hungry: Your body still needs the fuel. Aim for regular, smaller meals with protein in the middle of the plate.

2. Hydrate more than you think you should: People consistently underestimate this. Two to three litres a day, more if you're active.

If you're not sure how to adjust your routine around the medicine, message us. We see this every day, and there's almost always a small tweak that makes a big difference.

Less common, but worth knowing

A few side effects don't make the headlines but are reported in trials:¹

• Bloating, gas, belching, heartburn, or general "upset stomach"

• Headache or dizziness

• Mild, short-lived stomach pain

• Changes in how your skin feels

• Mood changes (some people feel flatter than usual, especially in the first few weeks)

Most of these settle. Hair thinning in particular is more about the rate of weight loss than the medicine itself, and it usually grows back once things stabilise.

When to contact us and when to call 999

Most side effects are uncomfortable but not dangerous. A few things, though, need urgent attention.

Call 999 or go to A&E if you experience:

• Severe stomach pain, especially if it spreads to your back

• Persistent vomiting that lasts more than 48 hours

• Signs of an allergic reaction (swelling of your face, lips or throat, severe rash, difficulty breathing)

• A racing or pounding heart that doesn't settle

• Yellowing of your skin or eyes (jaundice)

Message your Numan clinical team if:

• A side effect is sticking around longer than you'd expect

• You're not sure if what you're feeling is normal

• You're worried about anything at all

We'd rather hear from you and reassure you than have you sit with something you're unsure about.

The numan take

Side effects are part of the deal with this class of medicine, and pretending otherwise wouldn't help anyone. What we can tell you, with confidence, is that most people get through the first few weeks and come out the other side feeling much more like themselves, with the medicine quietly doing its job in the background.

References

1. Wharton S, Lingvay I, Bogdanski P, Duque do Vale R, Jacob S, Karlsson T, et al. Oral semaglutide at a dose of 25 mg in adults with overweight or obesity. N Engl J Med. 2025;393(11):1077–87.

2. Franz K, Otten L, Müller-Werdan U, Doehner W, Norman K. Severe weight loss and its association with fatigue in old patients at discharge from a geriatric hospital. Nutrients. 2019;11(10):E2415.