Metformin is the main medicine for type 2 diabetes. It works well and is generally safe.

But a rare side effect, lactic acidosis, has always been a focus for safety monitoring.

This article shows how pharmacovigilance (PV) helped update warnings and make metformin safer to use.

Early Concerns

Metformin is part of the biguanide class, which had problems in the past with phenformin (withdrawn for causing lactic acidosis).

When metformin came out:

• Boxed warnings were added for lactic acidosis
• Extra caution for people with kidney problems
• Limited use in elderly or hospitalized patients

Even though lactic acidosis was rare, these warnings influenced doctors for many years.

What Real-World Data Showed

PV studies and reports showed:

• Very few cases of lactic acidosis
• Less than 10 cases per 100,000 patients per year
• Most cases had other health problems like sepsis or heart failure

This meant metformin is very safe if used properly.

Label Changes

Thanks to PV data, labels were updated:

Now doctors have evidence-based guidance instead of strict bans.

Communicating Safety Changes (MICC)

PV also made sure safety updates reached everyone:

• Doctors know the new kidney limits
• Patients aren’t switched off metformin unnecessarily
• Labels are updated in software and guides
• Clear communication helped healthcare providers, pharmacists, and patients.

Lessons

• Past worries can affect decisions for decades
• Real-world data is key to balancing risk and benefit
• Labels change with new evidence
• MICC ensures updates are used in practice

Conclusion

Metformin is trusted not because it’s risk-free, but because PV helped understand and manage risks.