ME vs CFS: are they the same thing?
Mostly, yes. Today, most health bodies (including the US CDC, the UK’s NICE and Emerge Australia) use the combined term ME/CFS for one illness. The two names have different origins, though, and some people still draw a line between them.
| Myalgic encephalomyelitis (ME) | Chronic fatigue syndrome (CFS) | |
|---|---|---|
| Where the name came from | Used in the UK after a 1955 outbreak among staff at London’s Royal Free Hospital. The name means “muscle pain with inflammation of the brain and spinal cord”. | Coined by the US CDC in 1988 to describe a set of symptoms without assuming a cause |
| How it’s defined | Stricter definitions (e.g. the 2011 International Consensus Criteria) that require post-exertional malaise and neurological symptoms | Older definitions (e.g. Fukuda 1994) required six months of unexplained fatigue plus four of eight symptoms. PEM was optional. |
| The problem | “Encephalomyelitis” implies brain inflammation, which hasn’t been clearly proven in the way the name suggests | The name sounds like “being tired”, which trivialises the illness. Broad definitions also pulled in people with other conditions, muddying research. |
Where things stand now: modern criteria, such as the US Institute of Medicine (2015) and the Canadian Consensus Criteria, require post-exertional malaise. That brings “CFS” much closer to what was always meant by “ME”. The 2015 report even proposed a new name, systemic exertion intolerance disease (SEID), but it didn’t catch on.
“Chronic fatigue” vs “chronic fatigue syndrome”
These sound the same but aren’t:
- Chronic fatigue is a symptom: feeling tired for a long time. It has many causes, including anaemia, thyroid problems, sleep apnoea, depression, medications, cancer, autoimmune disease, overwork and poor sleep.
- Chronic fatigue syndrome (ME/CFS) is a specific illness defined by post-exertional malaise, unrefreshing sleep, reduced function for 6+ months, and brain fog and/or orthostatic intolerance.
That’s why doctors should rule out other causes before diagnosing ME/CFS. See Tests to ask your GP for.
ME/CFS and related conditions compared
| Condition | What it is | Key feature | How it relates to ME/CFS |
|---|---|---|---|
| ME/CFS | A multi-system illness affecting energy, immune and nervous systems | Post-exertional malaise (PEM): a delayed crash after exertion | — |
| Long COVID | An umbrella term for health problems lasting 3+ months after COVID-19 | Very varied: fatigue, breathlessness, brain fog, heart symptoms, loss of smell, and more | Many people with Long COVID meet ME/CFS criteria, especially those with PEM. Others have lung, heart or other problems instead. See After COVID vs glandular fever. |
| POTS (postural orthostatic tachycardia syndrome) | A form of dysautonomia: the nervous system doesn’t regulate heart rate and blood flow properly when upright | Heart rate rises 30+ bpm within 10 minutes of standing | Common alongside ME/CFS. Most people with ME/CFS have some orthostatic intolerance; a smaller share meet POTS criteria. See Dizziness on standing & POTS. |
| Orthostatic intolerance (OI) | The broader term for feeling worse when upright | Symptoms ease lying down | One of the core ME/CFS symptoms. POTS and orthostatic hypotension are specific types. |
| Fibromyalgia | A chronic pain condition | Widespread pain and tenderness, plus fatigue and poor sleep | Large overlap. Many people have both, and DecodeME found a shared genetic signal. Fibromyalgia doesn’t require PEM. |
| Post-infectious fatigue syndrome | Fatigue that persists after an infection | Fatigue after a clear infection | Many cases of ME/CFS start this way. Some people recover within months; others go on to meet ME/CFS criteria. |
| Depression | A mood disorder | Low mood and loss of interest or pleasure | Can co-occur, but is different. See below. |
| hEDS (hypermobile Ehlers-Danlos syndrome) | A connective tissue disorder | Very flexible joints, stretchy skin, easy bruising | Often seen alongside POTS and ME/CFS. |
| MCAS (mast cell activation syndrome) | Immune cells release too much histamine and similar chemicals | Flushing, itching, hives, food and chemical reactions | Reported more often in ME/CFS and POTS. A tryptase test can help. |
| Sleep apnoea | Breathing repeatedly stops during sleep | Snoring, gasping, unrefreshing sleep | Can mimic ME/CFS. It should be ruled out, and it’s treatable. See Sleep. |
How is ME/CFS different from POTS?
People are often diagnosed with one and later the other, so it’s worth being clear:
- POTS is about the heart rate response to standing. It’s diagnosed with a stand or tilt test. Many people with POTS don’t have post-exertional malaise.
- ME/CFS is about the energy system as a whole. Its hallmark is PEM after any kind of exertion, including mental effort, lying down.
- You can have both. Treating POTS (fluids, salt, compression, medications) often helps the dizziness and some of the brain fog of ME/CFS, but it doesn’t treat PEM.
- Exercise advice differs. Some POTS programmes use gradual, recumbent (lying or seated) exercise to recondition. If you also have ME/CFS, any exercise must stay inside your PEM threshold, which for many people means very little or none.
How is ME/CFS different from depression?
This matters because ME/CFS was misdiagnosed as depression for decades.
| ME/CFS | Depression | |
|---|---|---|
| Motivation | People usually want to do things but physically can’t | Loss of interest or pleasure in doing things |
| After exertion | Crash 12–72 hours later | Activity and exercise usually help mood |
| Other features | Flu-like symptoms, sore throat, tender glands, orthostatic intolerance | Persistent low mood, guilt, hopelessness |
People with ME/CFS can also develop depression or anxiety. That’s understandable with any serious, isolating illness, and it deserves treatment. But treating depression doesn’t cure ME/CFS, and exercise prescribed for depression can make ME/CFS worse.
Why getting every diagnosis right helps
Even though there’s no cure for ME/CFS yet, several of the conditions that come with it are treatable:
- POTS or orthostatic intolerance: fluids, salt, compression and medications
- Sleep apnoea: CPAP or a mouth splint
- MCAS: antihistamines and trigger avoidance
- Iron deficiency, thyroid problems, low vitamin D: straightforward to fix
Ask your doctor about each one. Fixing the treatable parts can make a real difference to how you feel day to day.