Like all medicines, short-acting insulin can cause side effects, although not everyone gets them. If you do have side effects such as problems where you inject, they usually happen in the first few weeks of starting insulin.
Common side effects
There are things you can do to help cope with these common side effects of short-acting insulin:
Hypoglycaemia (hypos)
Insulin can make your blood glucose levels fall too low (hypoglycaemia, or hypos).
Symptoms include:
- sweating
- trembling or shaking
- anxiety, confusion or difficulty concentrating
- fast heartbeat (palpitations)
- tingling lips
- changes to your vision such as blurred vision
- feeling dizzy
- feeling hungry
- paler than usual skin
If you start to get some of these symptoms, follow the instructions you've been given to treat a hypo and have a sugary drink or snack, such as a small glass of fruit juice or sugary fizzy drink, 5 glucose or dextrose tablets, 4 large jelly babies, or 2 tubes of glucose gel.
This type of sugar will not last long in your blood, so you may also need to eat a starchy carbohydrate once you blood glucose is back above 4mmol/L, like a sandwich or some biscuits, or your next meal if it's due.
You can reduce the chances of having a hypo by monitoring your blood glucose levels regularly and adjusting your insulin dose as advised by your doctor or diabetes nurse.
If you often get hypos, ask your doctor or diabetes nurse about getting a continuous glucose monitor or flash monitor, if you do not already have one.
This is a small sensor you wear on your skin that can show your blood glucose levels at any time. Most types have an alarm, which can wake you up if you get a hypo while you're asleep. You may be able to get a monitor free on the NHS.
Talk to your doctor or diabetes nurse if you often get hypos, or if you get them at night. It's likely you’ll need to adjust your insulin treatment.
Itching or redness where you inject
Try to avoid using any new soaps or bath products in the first few weeks of treatment, so that you'll know if any itching is caused by the insulin.
You can take an antihistamine to help ease the itching. Ask a pharmacist what type is suitable for you.
Itching and redness usually improves after about a week. If it does not get better, contact your doctor or diabetes nurse, as you may need to switch to a different type of insulin.
Pain when you inject
Always use a new needle for every injection. Rotate your injection sites by choosing a different place each time you inject, at least 1cm away from your last injection. You can use your tummy, the sides of your thighs or your buttocks.
Let your insulin warm up to room temperature before using it.
It can also help to try numbing the injection area by rubbing it with ice for 15 to 20 seconds before you inject.
If the pain does not stop or bothers you, contact your doctor or diabetes nurse to check your injection technique and make sure you're using the right size needle. Insulin needles come in different lengths, and a slightly longer or shorter needle could be better for your body shape.
Bleeding or bruising where you inject
Some people have some minor bleeding after injecting but this is not usually a problem. To reduce bruising, gently press the injection site for a few minutes after each injection.
If bleeding or bruising does not stop or bothers you, contact your doctor or diabetes nurse to check your injection technique and make sure you're using the right size needle. Insulin needles come in different lengths, and a slightly longer or shorter needle could be better for your body shape.
Fatty lumps under the skin (lipohypertrophy)
This can happen if you repeatedly use the same small area of your body to inject. It can look unsightly and can affect how the insulin is absorbed into your body.
To help reduce the chances of this happening, rotate your injection sites by choosing a different place each time you inject, at least 1cm away from your last injection. You can use your tummy, the sides of your thighs or your buttocks.
If you do get these lumps, do not inject in that area until it becomes soft and smooth again. This can take several weeks.
Changes in your vision
You may notice problems with your eyesight when you first start taking insulin, but this usually only lasts a short time.
Diabetes can also affect your vision, so you may have noticed your eyesight getting worse before you start insulin. You may find that your eyesight improves after a week or two as your blood glucose levels improve.
If it does not improve or you feel your eyesight is getting worse, speak to your doctor or diabetes nurse.
If you have diabetes you're eligible for free NHS sight tests.
If you've been diagnosed with diabetic retinopathy and you feel your eyesight is getting worse, contact your doctor or diabetes nurse.
Speak to your doctor or diabetes nurse if the advice on how to cope does not help and a side effect is still bothering you or does not go away.
Serious side effects
Insulin can sometimes cause severe hypos, where your blood glucose falls very low and you can become unconscious.
Speak to your doctor or diabetes nurse if:
- you've had severe hypos
- you do not always recognise the symptoms when you have a hypo
Immediate action required: Call 999 if:
You think someone's having a severe hypo and they're not responding normally or they're unconscious, and:
- a glucagon injection is not available or you do not know how to use it
- you've given a glucagon injection and they have not recovered within 10 minutes
- they've been drinking alcohol
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction to short-acting insulin (anaphylaxis).
Immediate action required: Call 999 now if:
- your lips, mouth, throat or tongue suddenly become swollen
- you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
- your throat feels tight or you're struggling to swallow
- your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
- you suddenly become very confused, drowsy or dizzy
- someone faints and cannot be woken up
- a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)
You or the person who's unwell may also have a rash that's swollen, raised, itchy, blistered or peeling.
These can be signs of a serious allergic reaction and may need immediate treatment in hospital.
Do not drive yourself to A&E.
The person you speak to at 999 will give you advice about what to do.
Other side effects
These are not all the side effects of short-acting insulin. For a full list, see the leaflet inside your medicine packet.
Reporting side effects
You can report any suspected side effect using the Yellow Card safety scheme.
Visit the Yellow Card website for more information about reporting side effects.