Diabetes: tablets for type 2 diabetes

Tablets that are used to treat type 2 diabetes mellitus are known as oral hypoglycaemics or antihyperglycaemics.

There are a number of different types of oral hypoglycaemics available for treating type 2 diabetes, and they work in different ways. They may be used on their own and some can be used in conjunction with each other, or with insulin.


Metformin (e.g. Diabex, Glucophage) is the only biguanide currently available in Australia. Metformin is generally the first choice hypoglycaemic medication prescribed for people with type 2 diabetes.

There are several combination medicines that contain metformin plus another type of oral hypoglycaemic medicine in one tablet. These include:

  • metformin plus a sulfonylurea — glibenclamide (brand name Glucovance);
  • metformin plus a glitazone — rosiglitazone (brand name Avandamet); and
  • metformin plus incretin enhancers — DPP-4 inhibitors, including sitagliptin (brand name Janumet), vildagliptin (brand name Galvumet), saxagliptin (brand name Kombiglyze), alogliptin (Nesina Met) and linagliptin (brand name Trajentamet).

How do they work?

Biguanides work by reducing the amount of glucose produced by the liver, increasing the uptake of glucose by muscle and fat cells, and slowing the absorption of glucose by the intestine. This in turn reduces the level of glucose in the bloodstream.

Side effects

Lactic acidosis

The most serious complication associated with metformin is lactic acidosis. This happens when lactic acid builds up in the body faster than it can be metabolised. It is a potentially fatal condition but is very rare.

When lactic acidosis occurs in people treated with metformin it is generally associated with old age, or people with kidney, liver or heart problems, those taking more than 2 grams of metformin per day, or those drinking excessive amounts of alcohol. People with severe kidney problems (renal failure) should not take metformin. Anyone who may have lactic acidosis should be taken immediately to the nearest accident or emergency department or receive urgent medical attention.

The symptoms of lactic acidosis are:

  • nausea, vomiting, stomach pain;
  • trouble breathing;
  • feeling weak, tired or generally unwell;
  • unusual muscle pain;
  • unusual sleepiness;
  • dizziness or light-headedness;
  • shivering, feeling extremely cold; and
  • slow heartbeat.

Other side effects

More common side effects of metformin include the following.

  • Nausea and diarrhoea. Your doctor will minimise the chance of you getting these by making gradual adjustments to your dose and by advising that you take the tablets at mealtimes.
  • Weight loss. Beneficial side effects of taking metformin that have been observed include weight loss (in overweight people), and improved lipid (cholesterol) levels.

When used on its own, metformin rarely causes hypoglycaemia (blood glucose levels that are too low).

When should you take them?

In order to reduce unwanted gastrointestinal side effects, medicines containing metformin should be taken with or at the end of a meal.


The sulfonylureas are an older, but very effective, group of antidiabetic agents. Sulfonylureas include the medicines:

  • glibenclamide (Daonil, Glimel);
  • gliclazide (e.g. Diamicron);
  • glimepiride (e.g. Amaryl, Aylide, Dimirel); and
  • glipizide (e.g. Melizide, Minidiab).

A combination medicine is available that contains both glibenclamide and metformin in one tablet (brand name Glucovance).

How do they work?

Sulfonylureas work by helping to stimulate the release of insulin by the pancreas. They may also have some effect in improving the sensitivity of the body's tissues to the action of insulin and in reducing the production of glucose by the liver.

Side effects

Possible side effects of sulfonylureas include weight gain, skin rashes and gastrointestinal disturbances.

They also increase the risk of hypoglycaemia, which can be life-threatening, particularly in elderly people or people with kidney or liver problems.

Many other medicines can interact with sulfonylureas, so be sure to tell your doctor about any other medicines you are taking.

When should you take them?

Sulfonylureas should be taken at mealtimes to reduce the risk of hypoglycaemia.

Thiazolidinediones (glitazones)

Pioglitazone (e.g. Actos, Vexazone) and rosiglitazone (brand name Avandia) are examples of a group of oral hypoglycaemic drugs called thiazolidinediones. These medicines may be used either on their own or in conjunction with other diabetes medicines.

A combination medicine that contains both rosiglitazone and metformin in one tablet is available (brand name Avandamet). These combination tablets can be prescribed for people who are already treated with both rosiglitazone and metformin, or those whose diabetes is not adequately controlled on either rosiglitazone or metformin alone.

How do they work?

Thiazolidinediones work by increasing the sensitivity of the body's tissues to the action of insulin, rather than stimulating insulin secretion. This allows glucose to be transported from the bloodstream into the body's fatty tissue, skeletal muscle and liver cells more efficiently.

Side effects

Side effects of the thiazolidinediones include:

  • fluid retention;
  • anaemia;
  • increased risk of bone fracture in women;
  • raised lipid levels;
  • weight gain; and
  • heart problems, such as heart failure or a possible increased risk of heart attack (rosiglitazone).

They are generally not prescribed for people who have heart failure or in the case of rosiglitazone, heart disease or angina.

When should you take them?

Thiazolidinediones are taken once or twice daily, with or without food. It may take 6 to 8 weeks to get the full effect of these drugs on blood sugar levels.

Alpha-glucosidase inhibitors

Acarbose (brand name Glucobay) is the only type of alpha-glucosidase available in Australia. Acarbose is sometimes prescribed in conjunction with biguanides or sulfonylureas.

How do they work?

The alpha-glucosidase inhibitors interfere with the function of some of the digestive enzymes (alpha glucosidases) that are involved in digesting carbohydrates. The effect is to slow carbohydrate digestion in the small intestine so that glucose (sugar) is not absorbed into the bloodstream so quickly. This decreases the blood glucose peaks which happen after a meal.

Side effects

Common side effects of alpha-glucosidase inhibitors include flatulence, diarrhoea and abdominal pain, especially upon initial treatment. However, starting at a low dose and gradually increasing it to the final dosage, rather than starting with the final dose, can help avoid these problems.

When should you take them?

Alpha-glucosidase inhibitors (acarbose) must be taken immediately before your meal, or with the first couple of mouthfuls, in order for them to work.

Incretin enhancers and mimetics

Incretin enhancers — also called dipeptidyl peptidase-4 (DPP-4) inhibitors — include:

  • sitagliptin (Januvia);
  • vildagliptin (Galvus);
  • saxagliptin (Onglyza);
  • alogliptin (Nesina); and
  • linagliptin (Trajenta).

Incretin mimetics — GLP-1 receptor antagonists — include:

  • exenatide (Byetta); and
  • liraglutide (Victoza).

Incretin enhancers are oral medicines, while incretin mimetics must be injected. These medicines are used in adults, and are used in combination with other oral diabetes medicines.

Available combination medicines include:

  • sitagliptin plus metformin (brand name Janumet);
  • vildagliptin plus metformin (brand name Galvumet);
  • saxagliptin plus metformin (Kombiglyze);
  • alogliptin plus metformin (Nesina Met); and
  • linagliptin plus metformin (Trajentamet).

These fixed-dose combination tablets can be prescribed for people who are already treated with both metformin and an incretin enhancer, or those whose diabetes is not adequately controlled on metformin alone.

How do they work?

Incretin enhancers and incretin mimetics work by increasing the production and release of insulin by the pancreas, as well as by reducing the production of glucose by the liver.

Incretin enhancers and mimetics work when blood glucose levels are high, especially just after a meal, but also help to lower blood sugar levels between meals.

On their own they are unlikely to cause hypoglycaemia, because they do not work when blood sugar levels are low.

Side effects

Side effects of incretin enhancers can include:

  • discomfort when swallowing;
  • headache, cold-like symptoms (alogliptin, linagliptin, sitagliptin and saxagliptin); and
  • dizziness and tremor (vildagliptin).

Side effects of incretin mimetics can include:

  • nausea;
  • decreased appetite;
  • headache; and
  • cold-like symptoms.

Pancreatitis (inflammation of the pancreas) is an uncommon side effect of both incretin enhancers and mimetics. These medicines need to be stopped if pancreatitis occurs.

When should you take them?

The incretin enhancers are taken once daily (or sometimes twice daily for vildagliptan), with or without food. They should be taken around the same time each day.

They are taken as combination therapy with metformin, a sulfonylurea or a thiazolidinedione. Combination medicines that contain an incretin enhancer plus metformin should be taken twice a day with meals.

Exenatide is injected twice a day, before breakfast and before dinner; liraglutide is injected once daily, around the same time each day.

Sodium-glucose co-transporter 2 (SGLT2) inhibitors

These medicines include:

  • dapagliflozin (Forxiga);
  • canagliflozin (Invokana); and
  • empagliflozin (Jardiance).

How do they work?

SGLT2 inhibitors act on the kidneys to increase the amount of glucose that is excreted in the urine, lowering the blood glucose level.

Side effects

Side effects include an increased risk of:

  • dehydration; and
  • genital and urinary tract infections.

Long-term side effects are still uncertain because these medicines are relatively new, but may include increased risk of bone fractures.

When should you take them?

SGLT2 inhibitors should be taken once daily.

Long-term outlook for people taking tablets for type 2 diabetes

It is not unusual for oral hypoglycaemics to control type 2 diabetes for a number of years, and then stop working. In fact, insulin treatment may be required in one-third of people with type 2 diabetes after 10-15 years of successful management using oral hypoglycaemic agents.

A healthy balance

Regardless of the type of diabetes you may have, it is important to recognise that medicines are only part of the overall treatment picture. It is just as important to follow both a healthy eating plan and a regular activity programme in order to maintain relatively stable blood glucose levels.

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