More than three million people take metformin for type 2 diabetes, with over 26 million prescriptions dispensed every year. While the medication carries several potential side effects, the NHS says most should ease within weeks as the body adjusts.
Pharmacist Raj Patel, who posts on TikTok as the "straight talking pharmacist", has outlined the problems people might face and what to do about them. He also shared one situation where treatment might need to be "temporarily paused".
How metformin works
Patel explained: "Think of your liver as a sugar tap. Even when you're not eating, it releases sugar into your blood. And if you have type 2 diabetes, that tap releases more sugar than your body needs."
"Metformin helps turn it down. It also helps the insulin that you make work better, so sugar can move out of your blood and into your cells, where it can be used for energy."
Common side effects listed by the NHS include nausea or vomiting, diarrhoea, tummy pain, loss of appetite, a change to the way things taste, and vitamin B12 deficiency, which can cause tiredness.
Managing nausea and B12 deficiency
On nausea and diarrhoea, Patel said: "Nausea and diarrhoea can happen, especially around starting treatment. Taking it with meals and a gradual prescribed dose increase can help."
He added: "If symptoms persist or disrupt your day. Ask whether the dose schedule or a modified release preparation needs reviewing. Do not increase, swap, or abandon treatment yourself."
Regarding B12 deficiency, he said: "Metformin can also lower vitamin B12. New pins and needles, unusual tiredness, or a sore red tongue deserve a review."
"They do not prove B12 deficiency. Ask whether a blood test is appropriate. Testing is advised when deficiency is suspected, and periodic checks may suit people with risk factors. You can usually continue metformin while low B12 is treated if it remains suitable."
When to pause treatment
Patel said a temporary pause might be needed during illness, but only after seeking advice from the medical team. He advised: "If you are vomiting, have diarrhoea, or have a high fever, get prompt advice from your diabetes team, pharmacist, or NHS 111 about your sick day plan."
"Dehydration may mean a temporary pause is needed. Following an existing clinical plan, ask when to restart. Do not wait for a routine review if you cannot keep fluids down."
