Tefor 500 mg and 850 mg film-coated tablets – metformin for type 2 diabetes

Tefor® is a medicine for the treatment of diabetes containing the active substance metformin (as metformin hydrochloride). It belongs to the group of oral antidiabetics called biguanides (ATC A10BA02). It is manufactured by Galenika a.d. Belgrade in two strengths: Tefor 500 mg and Tefor 850 mg film-coated tablets.

Metformin helps to lower blood glucose to normal levels in people whose body does not make enough insulin or does not use it properly. In overweight adults, long-term use also helps to reduce the risk of diabetes complications and is associated with stable body weight or modest weight loss.

What is Tefor (metformin) used for and how should it be taken correctly?

Basic information about the medicine

What is Tefor used for?

According to the package leaflet, Tefor is used to treat type 2 diabetes ("non-insulin-dependent diabetes") when diet and exercise alone are not enough to keep blood glucose under control, especially in overweight patients:

• adults may take Tefor alone or together with other medicines (oral antidiabetics or insulin);
• children aged 10 years and over and adolescents may take Tefor alone or together with insulin;
• in overweight adults, long-term use reduces the risk of diabetes complications.

How is Tefor taken and dosed?

Take the medicine exactly as your doctor has prescribed. Tefor does not replace a healthy lifestyle – continue with the prescribed diet and regular physical activity.

• Take the tablets with or after a meal – this reduces digestive side effects. Swallow each tablet with a glass of water; do not crush or chew them.
• One dose a day – in the morning with breakfast; two doses – with breakfast and dinner; three doses – with breakfast, lunch and dinner.
• Your doctor will check your blood glucose regularly and adjust the dose, and will check your kidney function at least once a year.
• If you also use insulin, your doctor will explain how to start treatment with Tefor.

Special patient groups

• Children and adolescents: the medicine can be used by children from 10 years; the nature and severity of side effects are similar to those in adults.
• Elderly: kidney function is checked more often; regular check-ups are especially important.
• Kidney impairment: with severely reduced function (GFR < 30 mL/min) the medicine is contraindicated; with milder impairment the dose is reduced.
• Liver impairment: do not take the medicine if you have liver problems (liver failure).

Contraindications – when the medicine must not be used

Do not take Tefor:

• if you are allergic to metformin or to any of the excipients;
• if you have liver problems (liver failure) or severely reduced kidney function;
• if you have uncontrolled diabetes with severe hyperglycaemia, nausea, vomiting, diarrhoea, rapid weight loss, lactic acidosis or ketoacidosis;
• if you have lost too much body fluid (dehydration), e.g. after long-lasting diarrhoea or repeated vomiting;
• if you have a severe infection (lungs, bronchi or kidneys);
• if you are being treated for acute heart failure, have recently had a heart attack, have severe circulation problems (shock) or breathing difficulties;
• if you drink alcohol excessively.

Precautions and warnings

• Lactic acidosis: the risk is higher with reduced kidney function, uncontrolled diabetes, serious infections, prolonged fasting, alcohol intake, dehydration, liver problems and conditions with reduced oxygen supply to tissues (e.g. acute heart failure).
• Contact your doctor immediately if you have an inherited mitochondrial disease (MELAS, MIDD) or if after starting treatment you notice seizures, declining cognitive abilities, difficulty with body movements, pain or numbness, migraine or hearing loss.
• Before an X-ray with iodinated contrast and before major surgery the medicine is stopped temporarily – the doctor decides when and for how long.
• Tefor alone does not cause hypoglycaemia, but with sulfonylureas, insulin or meglitinides there is a risk of low blood sugar (weakness, dizziness, sweating, fast heartbeat, vision problems, difficulty concentrating) – eating or drinking something with sugar usually helps.
• During treatment, the doctor checks kidney function at least once a year, more often in elderly people.

Interactions with other medicines, food and drink

Tell your doctor about all medicines you are taking; more frequent glucose and kidney tests or a dose change may be needed. The following are particularly important:

• iodinated contrast agents (Tefor is stopped temporarily);
• diuretics; medicines for pain and inflammation (NSAIDs and COX-2 inhibitors, e.g. ibuprofen, celecoxib); ACE inhibitors and angiotensin II receptor antagonists;
• beta-2 agonists (salbutamol, terbutaline) and corticosteroids;
• medicines that change the amount of metformin in the blood: verapamil, rifampicin, cimetidine, dolutegravir, ranolazine, trimethoprim, vandetanib, isavuconazole, crizotinib, olaparib;
• other medicines for diabetes.

Alcohol: avoid excessive intake as it increases the risk of lactic acidosis.

Pregnancy and breastfeeding

If you are pregnant, think you may be pregnant or are planning a pregnancy, talk to your doctor – a change of treatment or of glucose monitoring may be needed. Use of the medicine is not recommended if you are breastfeeding or plan to breastfeed.

Driving and using machines

Tefor alone does not cause hypoglycaemia and does not affect the ability to drive. Take care if you use it with medicines that can cause hypoglycaemia (sulfonylureas, insulin, meglitinides) – if you feel symptoms of low blood sugar, do not drive or use machines.

Possible side effects

• Very common (more than 1 in 10): nausea, vomiting, diarrhoea, stomach pain and loss of appetite – mostly at the start of treatment; dividing the dose and taking tablets with or right after meals helps. If symptoms persist, stop the medicine and contact your doctor.
• Common (up to 1 in 10): taste changes; reduced vitamin B12 in the blood (extreme tiredness, sore red tongue, pins and needles, pale or yellow skin).
• Very rare (up to 1 in 10,000): lactic acidosis; abnormal liver function tests or hepatitis; skin redness, itching or hives.

Overdose, missed dose and stopping treatment

• Overdose: may cause lactic acidosis (vomiting, stomach pain with cramps, weakness, difficulty breathing, low temperature, slow heartbeat) – stop the medicine immediately and seek urgent medical help.
• Missed dose: do not take a double dose; take the next dose at the usual time.
• Stopping treatment: any change or stop of treatment is decided by the doctor.

Related information

For blood sugar self-monitoring in diabetes, see also the category Blood sugar measuring devices – products in this category do not replace the medicine prescribed for you.

Composition, pack and manufacturer

• Active substance: metformin hydrochloride 500 mg or 850 mg per film-coated tablet.
• Excipients – core: povidone K 30; propylene glycol; microcrystalline cellulose; croscarmellose sodium; magnesium stearate. Film coating: hypromellose; talc; titanium dioxide; macrogol 6000.
• Tefor 500 mg: round, biconvex, white film-coated tablets; Al/PVC-PVC/PVdC blister with 10 tablets, 3 blisters per carton (30 tablets).
• Tefor 850 mg: oval, biconvex, white to almost white film-coated tablets; HDPE bottle with PP cap containing 30 tablets.
• Marketing authorisation holder and manufacturer: Galenika a.d. Belgrade. Authorisation numbers: 500 mg – 003105300 2024 of 11 September 2025; 850 mg – 515-01-02903-19-001 of 26 March 2020.

Storage

• Keep out of the sight and reach of children; if a child takes Tefor, use must be supervised by a parent or carer.
• Store below 25 °C in the original package in order to protect from light and moisture.
• Tefor 850 mg: after first opening the bottle, store below 25 °C in the original package for no longer than 30 days.
• Shelf life: 3 years; do not use after the expiry date stated on the pack.

Frequently asked questions

Does Tefor cause low blood sugar?

Not on its own. There is a risk of hypoglycaemia when Tefor is taken together with insulin, sulfonylureas or meglitinides.

When should I stop taking Tefor temporarily?

In conditions with fluid loss (vomiting, diarrhoea, fever, exposure to heat, low fluid intake), before and after an X-ray with iodinated contrast and before major surgery – always as instructed by your doctor.

Why does the doctor check vitamin B12?

Metformin can commonly reduce vitamin B12 levels in the blood. If extreme tiredness, a sore red tongue, tingling or pallor occur, the doctor will investigate the cause.

What is the difference between Tefor 500 mg and 850 mg?

They differ in strength and pack (500 mg in blisters, 850 mg in a bottle). The starting dose is usually 500 mg or 850 mg, and the doctor gradually adjusts it according to glucose values.

Sources

• ALIMS – Patient information leaflet Tefor 500 mg (PIL)
• ALIMS – Summary of product characteristics Tefor 500 mg (SmPC)
• ALIMS – Patient information leaflet Tefor 850 mg (PIL)
• ALIMS – Summary of product characteristics Tefor 850 mg (SmPC)

Sources checked on: 25 October 2026.