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Multiple Sclerosis (MS) Fatigue

What is multiple sclerosis (MS) fatigue?

​​​​​​​​​​​​​​​​​​​​​​​​​​Understanding MS fatigue and its effects can be helpful​ whether you have MS or know someone living with MS. On this page, you’ll find information about MS fatigue and why it happens. Visit other pages to find useful information on:

For support people, you’ll also find tips and information to identify and prevent burnout​.

What is MS fatigue?

Multiple sclerosis (MS) fatigue is a symptom of MS. It is overwhelming tiredness that changes what you can and cannot do.

MS fatigue can make it hard to do basic tasks and activities, no matter how much sleep or rest you get. Compared to someone without MS, you may feel much more tired after doing a task or activity. MS fatigue can affect how your body feels, your thoughts, reactions, and emotions.

MS fatigue is unique, different, and usually more severe than the tiredness experienced by people without MS.

  • It usually occurs every day, and tends to get worse throughout the day.
  • It can happen early in the morning, even if you’ve slept well.
  • Heat and humidity can make it worse.
  • It can start easily and without warning.
  • It is more likely to impact your day-to-day tasks.

When you have MS and aren’t able to do what you want to do or need to do during the day, you aren’t being lazy or unmotivated. You are experiencing the most common and disabling symptom of MS. Up to 95% of people living with MS experience fatigue, and over half describe fatigue as one of their most troubling symptoms. Fatigue is the most common reason that people with MS need to leave their workplace or change what they do at work.

MS fatigue is a symptom in all disease stages and sub-types. The severity of your fatigue is not linked to your age, gender, type of MS, or how long you’ve had MS.

People with MS describe their fatigue in many ways:

  • “I feel like I was hit by a truck.”
  • “It’s like I’m trying to walk through thick molasses.”
  • “I feel like my arms and legs are full of lead.”
  • “I can sleep 24 hours a day and still don’t feel rested.”
  • “I shouldn’t feel this tired.”
  • “It feels like I’m in a fog.”
  • “I’m so tired I can’t even think about doing anything.”

In addition to a feeling of extreme tiredness, MS fatigue can also cause communication challenges, difficulty swallowing, and less energy for family, relationships, and socializing. You may have noticed these experiences without knowing that they are part of MS fatigue:

  • Saying things like: “It’s on the tip of my tongue,” “I lost my train of thought,” or “I can see the word in my head but can’t get it out.”
  • Having people tell you that you are mumbling.
  • Choking on your spit, coughing, or feeling food sticking in your throat.
  • Not having energy for social gatherings or not being able to keep up in conversations.
  • Not having energy for intimacy.
  • Needing more time to get your energy back than you might expect.

From the outside, it can look like you are not experiencing fatigue. This is why many people with MS describe fatigue as an “invisible symptom.”

Why does MS fatigue happen?

For people without MS, there is usually a balance between how much energy you have available on a given day (energy storage) and how much energy you spend throughout the day. You can spend your energy in many ways, like doing things that are physical, doing things that are cognitively demanding (thinking tasks), or by regulating your emotions.

With MS, this energy use becomes out of balance in 3 ways:

  • It is harder to store energy, and so you have less energy available.
  • You spend more energy doing the same tasks than you used to.
  • It takes longer for energy levels to return, especially if you have done too much in one day.

In other words, with MS, there may not be enough energy to do all of the things you want or need to do throughout the day. And you may need more time, even several days, to get your energy back. This is how MS fatigue impacts what you can and cannot do.

Primary fatigue

MS fatigue can be divided into 2 types: primary and secondary fatigue.

Primary fatigue has to do with tiredness caused by the direct changes to the brain and spinal cord caused by MS. These changes create an inefficient nervous system, which uses more energy and causes fatigue. The changes can include myelin loss, changes to the immune system, and hormones.

Myelin loss is a breakdown of the myelin sheath, a covering for your nerve cells that helps messages travel quickly and accurately through your nervous system. Without myelin, you need to use more energy to get the message sent to where it needs to go. Heat is another factor that can slow the speed of messages.

Every message that moves through your central nervous system needs energy to travel, just like a car needs gas to get from one place to another. When MS breaks down your myelin, the road is harder to travel. The car may need to use more gas as it tries different routes, idles in traffic, or slows down through a construction zone. Primary fatigue happens because your gas tank empties more quickly with MS than without MS. The route the messages once took is no longer quick and direct.


​Using strategies will help you maximize your energy and manage your fatigue. Think of these like ways to save gas or ways to refuel the car.

Primary fatigue can affect your cognition, which includes how you think, process information, remember things, pay attention, and make decisions. When you are thinking, processing information, using your memory, or paying attention, your nervous system is sending messages to different parts of your brain. These messages are using energy, just like the messages needed to do physical tasks (like walking) use energy. If you have MS, you may need more energy to do these thinking tasks than someone without MS.

Secondary fatigue

Secondary fatigue is caused by other factors related to MS that are not direct changes to the brain and spinal cord.

Secondary fatigue can be caused by:

  • sleep disturbances (caused by restless legs, aches, or pains)
  • medicines that you are taking
  • low mood, depression, or increased stress
  • temperature sensitivity
  • muscles that are stiff, tight, or jerk uncontrollably (spasticity)
  • other medical conditions like anemia and hypothyroidism
  • obesity

MS fatigue is a complex issue. Primary fatigue can be made worse by secondary fatigue.

Learn more about how MS fatigue can impact daily living.


Current as of: September 14, 2023

Author: Calgary MS Program - Allied Health