Will metformin increase the risk of colon cancer by causing long-term diarrhea? How to reduce adverse reactions?

A friend asked Huazi that he had been suffering from diarrhea after taking metformin, and he was very worried that long-term diarrhea would damage the intestines and stimulate the incidence of colon cancer?

Huazi told him not to worry. The common adverse reaction of metformin is mainly gastrointestinal irritation, but it does not increase the risk of colorectal cancer. In addition, some retrospective studies have found that the incidence of various cancers may be slightly lower in patients with type 2 diabetes who use metformin for a long time.

1. Adverse reactions of metformin

Metformin is a relatively safe drug that does not affect the liver and kidneys . When used alone, it does not increase the risk of hypoglycemia . The most common adverse reaction is gastrointestinal reaction , which may cause nausea, vomiting, abdominal distension, diarrhea, abdominal pain, loss of appetite and other symptoms.

Gastrointestinal reactions caused by metformin usually occur in the first 1 to 2 months of medication , and will be tolerated and gradually alleviated with continued medication. The incidence of adverse reactions can be reduced by starting with a small dose, slowly increasing the dose, taking it with meals, and using a sustained-release formulation.

2. Effects of Metformin on Cancer

In animal experiments, it was found that metformin has a certain inhibitory effect on cancer cells through various mechanisms (such as affecting the energy metabolism of cancer cell mitochondria, activating the AMPK pathway, inhibiting PIK3CA mutations, etc.), and may have anti-cancer effects .

In some retrospective studies, the cancer incidence rate of metformin users was slightly lower than that of non-users. However, such studies have many confounding factors and limitations.

Multiple clinical trials are exploring the effects of metformin combined with chemotherapy, targeted therapy or immunotherapy on cancer, but the results are mixed and the evidence is insufficient.

At present, metformin has not been found to be carcinogenic , and may have certain anti-cancer effects, but further verification is still needed.

3. Rational use of drugs to reduce adverse reactions

1. Start with a low dose : It is recommended to start taking metformin at 500 mg per day. If no obvious adverse reactions occur, the dose should be doubled every 1 to 2 weeks until it reaches the optimal therapeutic dose of 2000 mg per day .

2. Choose a sustained-release dosage form : The ordinary dosage form of metformin has a greater irritation to the gastrointestinal tract. The enteric-coated dosage form can avoid direct irritation to the stomach. The sustained-release dosage form can slowly release the drug to minimize gastrointestinal irritation, so choosing a sustained-release dosage form will minimize adverse reactions .

3. Time of taking medicine : Enteric-coated dosage forms need to be taken on an empty stomach before meals, while ordinary dosage forms and sustained-release dosage forms need to be taken with meals to exert the advantages of the dosage forms and reduce adverse reactions.

4. Monitor renal function : Metformin will not harm the kidneys, but renal insufficiency will affect the excretion of metformin and increase the risk of lactic acidosis. Therefore, renal function should be checked regularly during medication. It is contraindicated when the eGFR is less than 30. When the eGFR is between 30 and 45, the risk needs to be assessed by a doctor.

5. Supplement vitamin B12 : Long-term use of metformin may affect the absorption of vitamin B12 and increase the risk of anemia and peripheral nerve damage. Therefore, it is necessary to check the level of vitamin B12 in the serum regularly and supplement it in time when it is deficient.

6. Beware of hypoglycemia : When metformin is used alone, it almost never causes hypoglycemia. However, when it is used in combination with other glucose-lowering drugs, it may increase the risk of hypoglycemia , so you need to be careful.

7. Stop the drug in special circumstances : If surgery or angiography is required, stop the drug 48 hours in advance and continue treatment after kidney function recovers. Stop the drug in case of severe infection or dehydration.

8. Maintain a healthy lifestyle : Excessive drinking and excessive dieting will aggravate gastrointestinal reactions and induce acidosis, so be careful to avoid them.

In summary, metformin does not increase the risk of cancer and may have a certain anti-cancer effect. The adverse reactions of metformin can be reduced through rational use of the drug. The drug must be used under the guidance of a doctor. If you have any questions about the use of the drug, please consult a doctor or pharmacist.

I am pharmacist Huazi. Welcome to follow me and share more health knowledge.