Managing side effects from your weight loss injection

Side effects from weight loss injections can usually be managed by checking your water intake, food patterns and dose timing before considering any change to the medication. Doctors do not recommend taking half doses as that is not how these medications are prescribed and it runs the risk of over/underdosing. If side effects are severe or not improving, a dose change may be appropriate.

Who this applies to

This article applies to patients currently on a weight loss injection (Mounjaro or Wegovy) who are experiencing side effects. If your side effects are severe (such as significant abdominal pain, persistent vomiting, or signs of an allergic reaction), contact 999, your GP or NHS 111 rather than waiting for our response.

First things to check

Before changing dose, the doctors will want to know whether the basics are in place:

• Water intake. Many patients do not realise they need to drink 2-3 litres of water a day on weight loss injections. Low water intake can cause nausea, headaches and constipation. This can also cause more of the more serious side effects as well if you become dehydrated
• Food patterns. Eating smaller more frequent meals, rather than three large meals, tends to reduce side effects. Keep a food diary; a specific food may be triggering the issue.
• Dose timing. If you have come up the doses too quickly, your body may not have been ready for the higher strength. Going back down a level may help. 

Half doses and dose reductions

Doctors will not recommend taking half doses, this can cause side effects and potential under/overdosing which means OOP cannot confirm your safety. The medication is not prescribed or licensed for that and the doctors cannot continue to prescribe to you if you are taking it that way.

If side effects are not improving and you have given the basics time to work, the doctors may consider stepping you down to a lower strength. This is decided case by case.

Ordering a new pen at a lower dose

If a dose reduction is appropriate, you can place a new order for a lower-strength pen or if you already have an active order you can email customer service who can amend the order for you and refund any difference in price if there is one. Some doctors will approve this depending on your circumstances. 

Common scenarios

• You have just moved up a dose and the side effects are worse than the previous level. Check water and food first, and consider stepping back down if they do not settle.
• You have been on the same dose for a while and side effects have come back. A food diary often reveals the cause.
• You are tempted to take half a dose to make it more manageable. This is not recommended; speak to us first.

What to do next

Start with the basics: 2-3 litres of water a day, smaller and more frequent meals, and a brief food diary. If side effects are not improving after a week of this, contact us with details of your dose, how long you have been on it, what side effects you are experiencing, and what you have already tried.

Still need help?

See our Contact us article for the best way to reach our team.