Diclofenac: what it does and what to watch
Also known as: Diclofenac sodium, Diclofenac potassium, Diclofenac diethylamine · NSAID (nonsteroidal anti-inflammatory pain reliever) · Updated 2026-10-25 · Educational — not medical advice
In plain language: It blocks the enzymes that manufacture prostaglandins, the chemical messengers responsible for pain, swelling, and fever at an injury site. Those same prostaglandins normally protect the stomach lining and help the kidneys manage blood flow, so blocking them broadly is what makes this medicine effective against inflammation while also being the source of its main risks to the gut, kidneys, and cardiovascular system.
What it's used for
- Pain and inflammation from arthritis
- Muscle and joint injuries
- Menstrual cramps
- Post-surgical or dental pain
Common side effects
- Stomach upset or heartburn
- Headache
- Dizziness
- Fluid retention or mild swelling
- Nausea
- Skin rash
Get medical help if…
Vomiting blood or vomit that looks like coffee grounds: go to an emergency department now. Black or tarry stools (possible bleeding in the gut): contact a doctor straight away
Chest pain, shortness of breath, sudden weakness on one side or trouble speaking (possible heart attack or stroke): call emergency services now
Reduced urination, swelling, or unusual tiredness (possible kidney strain)
Severe stomach pain that doesn't ease
Facial swelling or difficulty breathing: call emergency services now. A severe skin reaction, especially with blisters or peeling: go to an emergency department now
Lab values it can move
Few guides tell you this part: medicines show up in blood work. If you take Diclofenac and a value below looks off on your report, this may be part of the story — never stop a medicine without your doctor.
By reducing blood flow through the kidneys, this medicine can push creatinine upward, especially with frequent use, dehydration, or existing kidney concerns.
CreatinineSlow, often unnoticed blood loss from stomach lining irritation can gradually lower hemoglobin, sometimes before any stomach symptoms are even noticed.
HemoglobinGood to know
- Carries a combined caution for the heart, kidneys, and stomach, so it's generally used at the lowest amount for the shortest time that controls symptoms
- People with existing heart disease, high blood pressure, or kidney disease are usually advised to use it carefully and under medical guidance
- Not usually recommended at any stage of pregnancy, and it should not be taken from about 20 weeks unless a doctor advises it; paracetamol is generally the first choice of painkiller in pregnancy
- Taking it with food reduces stomach irritation
- Avoid combining with other NSAIDs or without checking first if already on blood thinners or steroids
- Check with a doctor first if you have asthma, or have ever had wheezing or other side effects from NSAIDs such as ibuprofen or naproxen
Questions people ask
Why does diclofenac carry heart, kidney, and stomach warnings all at once?
All three risks trace back to the same mechanism: blocking the prostaglandins that cause inflammation also blocks prostaglandins that protect the stomach lining, keep blood flowing properly through the kidneys, and help balance clotting and blood vessel tone. That's why this class of medicine is watched from several angles rather than just one, particularly with frequent or prolonged use.
Why is diclofenac avoided late in pregnancy?
In the later stages of pregnancy, this type of medicine can affect blood flow in the developing baby and has been linked to complications affecting the heart and blood vessels around birth, as well as reduced amniotic fluid. Because of these specific concerns, it's generally avoided in the second half of pregnancy (from about 20 weeks) unless a doctor has decided the benefit clearly outweighs the risk in a particular situation.
Sources
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