Causes of fatigue

Although it has one name, there are two recognised types of fatigue in MS: fatigue caused by nerve damage (primary fatigue), and fatigue caused by factors related to MS (secondary fatigue). Your fatigue could be due to one of these factors, or a combination.

Fatigue caused by nerve damage (primary fatigue)

When fatigue is thought to be a direct result of damage to the central nervous system, like demyelination or inflammation, we call it 'primary fatigue'.

MS fatigue and the central nervous system

Some studies suggest certain parts of the brain are linked to MS fatigue. But no single area of the brain has been identified. It could be caused by damage in several areas of the brain or spinal cord.

Some researchers suggest fatigue might be caused by the way that the brain adapts to the impact of MS. MRI scans of people who have fatigue show they use larger areas of the brain to carry out activities than people without fatigue.

Perhaps the brain is finding new routes for messages when the usual nerve paths have been affected. Finding new routes might mean it takes more energy to carry out an action, and this might cause fatigue.

But there are other processes in the brain and spinal cord that might also have an effect. We don’t yet know for sure if there is an exact link between nerve damage and fatigue.

Fatigue caused by factors related to MS (secondary fatigue)

Secondary fatigue is the result of factors that may be related to MS, but are not MS itself.

These include:

Other MS symptoms

Muscle weakness, stiffness, pain, tremor and depression may lead to feelings of fatigue.

Living with MS

Lack of sleep, or disturbed sleep caused by things like bladder problems or muscle spasms, might also cause fatigue.

If you are less mobile and, as a result, less fit than you once were, you might have lower energy levels.

Some people also find that living with MS causes anxiety or low mood and that this adds to feelings of fatigue. For more on this, see our section on MS and mental health.

Very often, heat makes fatigue worse for people with MS. Changes in the weather, an overheated room or physical exertion can all have a temporary effect.


Infections can also raise the body’s temperature and make fatigue worse until your temperature returns to normal.


Many common drugs used to manage MS and related symptoms have side effects that add to fatigue. If you start a new medication, change doses, or the time you take it, your fatigue levels might also change. Discuss any changes with the prescribing doctor – don’t adjust your drugs without advice.

I explain fatigue to my friends by reminding them how they feel just after they've got over a bad case of flu. Add to that the feeling of a really bad hangover, and you have some idea of what fatigue is like.
Chris, living with primary progressive MS