55 side effects
| Side effect | Frequency | MedlinePlus | PubMed Central (PMC) | Mayo Clinic Connect | NHS |
|---|
| Lactic Acidosis | rare | lactic acidosis | — | — | — |
| Extreme Tiredness | — | extreme tiredness | — | — | Tiredness |
| Weakness | — | weakness | — | — | — |
| Discomfort | common | discomfort | abdominal discomfort | Digestive System issues | Stomach ache |
| Nausea | common | nausea | nausea | nausea | Nausea |
| Vomiting | common | vomiting | vomiting | — | Vomiting |
| Stomach Pain | common | stomach pain | — | — | Stomach ache |
| Decreased Appetite | common | decreased appetite | — | — | Loss of appetite |
| Deep and Rapid Breathing | rare | deep and rapid breathing | — | — | Rapid breathing |
| Shortness of Breath | — | shortness of breath | — | — | Breathlessness |
| Dizziness | rare | dizziness | — | — | Dizziness |
| Lightheadedness | — | lightheadedness | — | — | Faintness |
| Fast Heartbeat | rare | fast heartbeat | — | — | Fast or shallow breathing |
| Slow Heartbeat | rare | slow heartbeat | — | — | Slow heartbeat |
| Muscle Pain | common | muscle pain | — | — | — |
| Feeling Cold | — | feeling cold | — | — | — |
| Diarrhea | common | diarrhea | diarrhea | severe diarrhea | Diarrhoea |
| Stomach Discomfort | common | stomach discomfort | abdominal discomfort | Digestive System issues | Stomach ache |
| Indigestion | common | indigestion | dyspepsia | — | — |
| Constipation | common | constipation | — | severe constipation | — |
| Lack of Energy | common | lack of energy or weakness | — | — | Severe tiredness |
| Change in Sense of Taste | common | change in sense of taste | — | — | Metallic taste |
| Headache | common | headache | — | — | — |
| Flushing of the Skin | common | flushing of the skin | — | — | — |
| Nail Changes | common | nail changes | — | — | — |
| Rash | common | rash | — | — | Rash |
| Chest Pain | — | chest pain | — | — | — |
| Hypoglycemia | — | hypoglycemia | — | — | Low blood sugar |
| Abnormal Heartbeat | rare | abnormally fast or slow heartbeat | — | — | Fast or shallow breathing |
| Weight Loss | common | — | Weight Loss | — | — |
| Abdominal Discomfort | common | — | abdominal discomfort | Digestive System issues | Stomach ache |
| Flatulence | common | — | flatulence | — | — |
| Dyspepsia | common | — | dyspepsia | — | — |
| Fecal Incontinence | uncommon | — | fecal incontinence | — | — |
| Mood Swings | common | — | — | mood swings | — |
| GI Problems | common | — | — | GI problems | — |
| Bloating | common | — | — | bloating | — |
| Severe Constipation | uncommon | — | — | severe constipation | — |
| Loud Gurgles | uncommon | — | — | loud gurgles | — |
| Metallic Taste | common | — | — | — | Metallic taste |
| Vitamin B12 Deficiency | — | — | — | — | Vitamin B12 deficiency |
| Low Blood Sugar | — | — | — | — | Low blood sugar |
| Breathlessness | — | — | — | — | Breathlessness |
| Faintness | — | — | — | — | Faintness |
| Serious Allergic Reaction | rare | — | — | — | Serious allergic reaction |
| Swollen Lips | rare | — | — | — | Swollen lips, mouth, throat or tongue |
| Confusion | rare | — | — | — | Confusion |
| Drowsiness | rare | — | — | — | Drowsiness |
| Liver Problems | rare | — | — | — | Liver problems |
| Yellow Skin or Eyes | rare | — | — | — | Yellow skin or eyes |
| General Feeling of Being Unwell | rare | — | — | — | General feeling of being unwell |
| Severe Tiredness | rare | — | — | — | Severe tiredness |
| Fast or Shallow Breathing | rare | — | — | — | Fast or shallow breathing |
| Tight Throat | rare | — | — | — | Tight throat |
| Struggling to Breathe | rare | — | — | — | Struggling to breathe |
11 additional sourcesdidn't return structured side-effect data: Ncbi.nlm.nih.gov, Mayo Clinic, WebMD, RxList, GoodRx, YouTube · JJ Medicine, Cleveland Clinic, Weight Watchers, Herald Scholarly Open Access, Reddit, Healthdirect.gov.au.
Demographic risk groups
| Group | Risk | Sources |
|---|
| kidney disease patients | higher risk of lactic acidosis | MedlinePlus |
| patients over 65 years old | higher risk of lactic acidosis | MedlinePlus |
| patients with heart disease | higher risk of lactic acidosis | MedlinePlus |
| patients with liver disease | higher risk of lactic acidosis | MedlinePlus |
| pregnant | Contraception may not protect from pregnancy | MedlinePlus, NHS |
| children | Serious allergic reaction | MedlinePlus, NHS |
| lean individuals with type 2 diabetes | higher risk of weight loss | PubMed Central (PMC) |
| elderly | higher risk of diarrhea | PubMed Central (PMC) |
| patients with nephropathy | increased metformin levels | PubMed Central (PMC) |
| People with kidney problems | Low blood sugar may happen | NHS |
| People with liver problems | Low blood sugar may happen | NHS |
| People with brown or black skin | Difficulty noticing yellow skin or eyes | NHS |