Managing common side effects

Side effects occur because weight loss injections influence how your body processes food, appetite, and digestion. These medications work by slowing the rate of food leaving the stomach and affecting hunger hormones, which can sometimes lead to digestive changes, fatigue, or nausea. While most side effects are mild and temporary, knowing how to handle them can help make your treatment more comfortable and effective.

Side effects

"Side effects are normal, and most can be managed at home without interrupting your treatment. Below are the most common side effects, the best ways to handle them, and when you should speak to your doctor."

Dr. Babak Ashrafi
Dr Babak Ashrafi Clinical Lead for Service Expansion
Accreditations: BSc, MBBS, MRCGP (2008)

Nausea

Why it happens:

Weight loss injections slow digestion, meaning food stays in your stomach longer, which can sometimes cause nausea, especially after eating.

How to manage it:

  • Eat smaller, more frequent meals rather than large portions.
  • Avoid rich, spicy, or fatty foods, which can make nausea worse.
  • Stay hydrated by sipping water or herbal teas throughout the day.
  • Take anti-sickness medication if needed—you can get suitable options over the counter at your local pharmacy.
  • Try eating bland foods like toast, crackers, or bananas if you’re feeling queasy.
  • Ginger or peppermint tea can also help settle your stomach.

When to see a doctor:

If nausea is persistent, worsening, or accompanied by vomiting that prevents you from keeping fluids down, it’s time to seek medical advice.

Constipation

Why it happens:

Weight loss injections can slow digestion, which may lead to constipation in some people.

How to manage it:

  • Increase your fibre intake by eating more vegetables, whole grains, nuts, and seeds.
  • Drink at least 2 litres of water daily to help keep stools soft.
  • Engage in regular physical activity, like walking or light exercise, to stimulate digestion.
  • Use a mild laxative if necessary—your pharmacist can recommend a safe option.
  • Try probiotics or foods rich in gut-friendly bacteria, like yogurt or kefir, to promote healthy digestion.

When to see a doctor:

If constipation becomes severe, lasts longer than a few days, or causes discomfort, bloating, or vomiting, consult a doctor for guidance.

Diarrhoea

Why it happens:

Some people experience diarrhoea as their body adjusts to the medication, particularly if their diet has changed significantly.

How to manage it:

  • Stay hydrated with plenty of clear fluids, such as water or oral rehydration solutions.
  • Avoid greasy, fatty, or processed foods, which can make diarrhoea worse.
  • Eat small, bland meals such as rice, toast, or bananas to help settle your stomach.
  • Consider taking an over-the-counter anti-diarrhoea treatment if needed.
  • Avoid caffeine and alcohol, which can irritate the digestive tract.

When to see a doctor:

If diarrhoea lasts more than a few days, becomes severe, or is accompanied by dehydration symptoms (such as dizziness, dry mouth, or dark urine), seek medical advice.

Mild fatigue

Why it happens:

Weight loss injections impact metabolism, and as your body adjusts to a lower calorie intake, you may feel more tired than usual.

How to manage it:

  • Ensure you’re getting enough sleep—aim for at least 7–9 hours per night.
  • Engage in light physical activity, such as a short walk or gentle stretching, to boost energy levels.
  • Eat a balanced diet and make sure you’re consuming enough calories for safe, sustainable weight loss:
  • For men, this is usually 1,900–2,000 calories a day.
  • For women, 1,400–1,500 calories a day is generally recommended.
  • Stay hydrated—dehydration can contribute to feelings of fatigue.

When to see a doctor:

If fatigue becomes extreme, affects your daily life, or doesn’t improve, speak to a doctor to rule out any underlying causes.

Vomiting

Why it happens:

In some cases, weight loss injections may cause nausea severe enough to lead to vomiting, particularly if you eat too much or too quickly.

How to manage it:

  • Follow the same recommendations as for nausea (smaller meals, bland foods, and hydration).
  • Sip clear fluids frequently to prevent dehydration.
  • Avoid lying down immediately after eating, as this can make symptoms worse.
  • Take small sips of rehydration solutions if vomiting persists.

When to see a doctor:

If vomiting is severe, doesn’t improve, or is accompanied by dehydration or abdominal pain, seek medical attention.

Other less common side effects

While the above symptoms are the most common, some people may experience:

  • Headaches: Often due to dehydration or reduced food intake—drink more water and avoid skipping meals.
  • Dizziness: Can result from dehydration or low blood sugar—make sure you’re eating enough and staying hydrated.
  • Heartburn or indigestion: Try eating slowly, avoiding acidic or spicy foods, and elevating your head while sleeping.
  • Sulphur burps: These can occur when food remains in the stomach for longer than usual, allowing it to ferment and release gases like hydrogen sulfide. The same strategies used for managing heartburn —eating smaller meals slowly, avoiding acidic or spicy foods, and elevating your head while sleeping—can be helpful here too.

If any of these symptoms persist or become severe, consult a doctor.

When to get medical help

While most side effects are mild, it’s important to know when to seek medical attention. Contact a doctor if:

  • You experience severe or persistent nausea, vomiting, or diarrhoea.
  • You notice signs of dehydration such as dark urine, dizziness, or confusion.
  • You have severe abdominal pain that doesn’t go away.
  • Your fatigue is extreme or affecting your daily life.
  • You develop any unexpected symptoms that worry you.

For mild concerns, you can reach out via your ZAVA patient account, where we’re always here to help. If symptoms become severe or difficult to manage, call 111 for urgent medical advice—or 999 in an emergency.

Quick tips for managing side effects

Dizziness

Nausea

  • Eat smaller, more frequent meals
  • Avoid rich, spicy, or fatty foods
  • Stay hydrated!
  • Take anti-sickness medication if needed
Constipation

Constipation

  • Increase your fibre intake
  • Drink more water!
  • Engage in regular physical activity
  • Use a mild laxative if necessary
Diarrhoea

Diarrhoea

  • Stay hydrated with plenty of clear fluids
  • Avoid greasy, fatty, or processed foods
  • Eat small, bland meals
  • Consider taking an over-the-counter treatment
Fatigue

Mild fatigue

  • Ensure you’re getting enough sleep (7–9 hours)
  • Engage in light physical activity
  • Eat a balanced diet
Dizziness

Vomiting

  • Follow the same recommendations for nausea
  • Sip clear fluids frequently
  • Avoid lying down immediately after eating
David Meinertz

How long do side effects last?

For most people, side effects are temporary and should improve within the first few weeks of treatment. Here’s what to expect:

  • First few days: Nausea and mild digestive changes are most common.
  • First few weeks: The body adapts, and side effects like nausea and constipation usually improve.
  • First few months: Most side effects settle down, but some may persist or return during dose increases. If side effects are hard to manage or not improving, it may help to stay on a lower dose for longer. You can also try reducing the dose temporarily to give your body more time to adjust.

David Meinertz

How common are side effects?

Most people experience at least one mild side effect when starting weight loss injections, but they usually improve as the body adjusts.

  • Very common (experienced by more than 1 in 10 people): Nausea, constipation, diarrhoea, mild fatigue.
  • Common (experienced by up to 1 in 10 people): Vomiting, headaches, dizziness, acid reflux.
  • Less common (experienced by fewer than 1 in 100 people): Abdominal pain, bloating, dehydration symptoms.

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