A sulfonylurea (type 2 diabetes tablet)
Gliclazide
A sulfonylurea tablet that lowers blood sugar in type 2 diabetes by prompting the pancreas to release more insulin — effective, but it can cause low blood sugar.
What is Gliclazide?
Gliclazide is a sulfonylurea medicine for type 2 diabetes that helps the pancreas release more insulin. It is often added when metformin alone is not keeping blood sugar under control, to lower glucose levels and ease the symptoms of high blood sugar, which over time helps reduce the risk of diabetes-related problems.
Education and reference only. This is a plain-language guide to Gliclazide — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Gliclazide is one of the most commonly used sulfonylureas in the UK for type 2 diabetes. It is often added when metformin alone is not controlling blood sugar, or used when metformin is not suitable. Unlike metformin, which works mainly in the background, gliclazide actively lowers blood sugar by squeezing more insulin out of the pancreas — which makes it effective but also means it can push blood sugar too low. It is taken as a long-term tablet, usually with or just before a meal.
How it works
Gliclazide attaches to the insulin-producing (beta) cells in the pancreas and prompts them to release more insulin. The extra insulin moves sugar out of the blood and into the body's cells, so blood-glucose levels fall. Because it makes the pancreas release insulin whether or not you have eaten, the blood sugar can drop too low (a "hypo") — particularly if a meal is skipped, delayed or smaller than usual, or after extra exercise or alcohol. This is the key difference from metformin, which does not usually cause hypos on its own.
Company & origin
Originated / developed by: Servier (Les Laboratoires Servier, France).
Gliclazide is a second-generation sulfonylurea developed by the French company Servier and introduced in the early 1970s, with regulatory approvals following in subsequent years (it was approved in Japan in 1984). It has long been marketed under the brand Diamicron.
What it treats
Conditions Gliclazide is used for
Practical use
How to take Gliclazide
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Usually taken with or just before a meal, most often breakfast, so that it works alongside food.
- Take it regularly at around the same time each day, and do not skip meals after taking it, as missing food raises the risk of a 'hypo' (low blood sugar).
- If you miss a dose, leave it out and carry on with your next one with food; never double up to make up for a missed dose.
- Learn to recognise hypo warning signs (shakiness, sweating, hunger, confusion) and carry a fast-acting sugar source, especially when driving or active.
- Keep up your blood-glucose monitoring and routine HbA1c checks so your team can review whether the dose still suits you.
- Do not stop suddenly without advice; let your prescriber know about illness, fasting, alcohol or major changes in activity.
Weighing it up
Advantages & disadvantages of Gliclazide
Advantages
- Long-established and well understood, with decades of UK clinical experience.
- Effective at lowering blood sugar and a useful add-on when metformin is not enough.
- Taken by mouth and generally inexpensive and widely available.
- Works relatively quickly compared with some other diabetes tablets.
Disadvantages
- Can cause low blood sugar (hypoglycaemia), which can be serious, particularly in older people or if meals are missed.
- Tends to cause some weight gain rather than weight loss.
- Does not have the heart and kidney protective benefits seen with some newer diabetes medicines.
- May become less effective over time as diabetes progresses, sometimes needing additional treatment.
Practical use
Good to know
It is taken with or just before a meal so the insulin it releases matches the food coming in; skipping that meal is the classic trigger for a hypo. It tends to cause some weight gain, which is worth knowing if weight is a concern. Because it can cause low blood sugar, it matters for driving — know the symptoms of a hypo (shakiness, sweating, hunger, confusion), carry a fast-acting sugar, and don't drive if your sugar is low. Alcohol and missed meals both raise hypo risk. Over time the pancreas may make less insulin, so the tablet can become less effective and the treatment plan may need reviewing.
Who should not take it / use with caution
- People with type 1 diabetes or in a diabetic emergency (such as ketoacidosis) — these need insulin, not a sulfonylurea.
- People with severe liver or kidney impairment, where the risk of prolonged low blood sugar is higher.
- Used with caution in older or frail people, those who eat irregularly, and in pregnancy or breastfeeding, where other treatments are usually preferred.
Monitoring
- Blood-glucose control (including HbA1c blood test)
- Hypo episodes and awareness of warning signs
- Weight, and kidney and liver function where relevant
Side effects
- Low blood sugar (hypoglycaemia) — the most important effect; symptoms include sweating, shakiness, hunger, irritability and confusion, and it needs treating quickly with fast-acting sugar.
- Weight gain, which some people find significant.
- Occasional digestive upset; rarely, skin rashes, or changes in blood counts or liver tests.
Key interactions
- Other glucose-lowering medicines (including insulin) add to the hypo risk, so the combination is balanced carefully.
- Alcohol can lower blood sugar further and mask hypo warning signs.
- Some medicines — certain antibiotics, antifungals and others — can raise or lower its effect; warfarin and a few drugs need extra care.
Available as: Tablets, including a standard form and a modified-release form taken once a day. The two are not swapped like-for-like, so it is best to stay on the form you were prescribed.
Answers
Gliclazide: frequently asked questions
Why can gliclazide cause low blood sugar when metformin usually doesn't?
Gliclazide makes the pancreas release more insulin whether or not you have eaten, so if a meal is missed or delayed the blood sugar can drop too low. Metformin works differently — it mainly reduces the sugar the liver makes and helps the body use insulin better — so on its own it rarely causes a hypo. This is why hypo awareness matters more with gliclazide.
What should I do if I am going to miss a meal?
Because gliclazide is timed to a meal, skipping that meal is the main cause of a hypo. Speak to your diabetes team about what to do on days you eat less or fast — they may advise adjusting timing. Always carry a fast-acting sugar (such as glucose tablets or a sugary drink) in case your sugar drops.
Can I drive while taking gliclazide?
Yes, but because gliclazide can cause hypos you must manage that risk: check your blood sugar as advised before driving, don't drive if it is low, keep fast-acting sugar in the car, and learn your hypo warning signs. There are DVLA rules for diabetes treated with medicines that can cause hypos — your team can explain what applies to you.
Will gliclazide make me put on weight?
Some weight gain is common with sulfonylureas, partly because of the extra insulin. If weight is a concern, mention it — there are alternative diabetes medicines that are weight-neutral or help with weight loss, and your team can weigh up the options with you.
What is the difference between gliclazide and Diamicron?
They are the same medicine — gliclazide is the generic (active-ingredient) name and Diamicron is a brand name. Generic gliclazide contains the identical active ingredient.
The wider class
About Sulfonylureas
Gliclazide belongs to the sulfonylureas class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
Browse by body system
Authoritative sources
- BNF: Gliclazide.
- electronic Medicines Compendium (SmPC): Gliclazide (Diamicron).
- NICE CKS: Gliclazide.
Keep reading
Related articles
Building a medicines information resource?
We create evidence-led, dose-free drug and formulary references for teams.