On the surface, chronic fatigue syndrome (ME/CFS) and attention deficit/hyperactivity disorder (ADHD) look like complete opposites: One means you have to stay inactive much of the time, and the other one makes you constantly active. They couldn't have much of anything in common, right?

Actually, they just might.

Researchers exploring a possible link between ME/CFS and adult ADHD say fatigue may be an important ADHD symptom, and that doctors should look for ADHD, or a history of it, in people with ME/CFS or other types of persistent fatigue.

Early Research Into an ADHD/ME/CFS Link

In 2007, a study led by JL Young looked at a possible connection between ADHD (inattentive type), ME/CFS, and fibromyalgia. According to the abstract:

"In an outpatient psychiatric clinic, a number of adult patients who presented primarily with symptoms of ADHD, predominately inattentive type, also reported unexplained fatigue, widespread musculoskeletal pain or a pre-existing diagnosis of CFS or FMS. As expected, ADHD pharmacotherapy usually [improved] the core ADHD symptoms of inattention, distractibility, hyperactivity, and impulsivity. Less expected was the observation that some patients also reported [improvement] of pain and fatigue symptoms."

This finding led to increased interest in the use of ADHD medications—such as Ritalin—to relieve some of the cognitive challenges related to ME/CFS and other kinds of chronic fatigue.

2013 Study Supports Findings

Young's later study looked at three cases of ME/CFS in people who'd responded poorly to treatment. Researchers found that all three met the criteria for ADHD, and all three responded well to psychostimulant medications, which are a common part of ADHD treatment. They say the patients saw improvements in fatigue, pain, cognitive dysfunction, and other symptoms. According to their abstract:

"...all patients were found to meet criteria for attention-deficit/hyperactivity disorder (ADHD) and underwent a standard regimen of a psychostimulant medication. After treatment with psychostimulants, the 3 patients reported improved symptoms of fatigue and pain, and cognitive and core ADHD symptoms."

Researchers concluded that ADHD and ME/CFS may share a common underlying mechanism and that over time, ADHD may develop into chronic fatigue syndrome and pain. (It's unclear whether this would most appropriately be considered a new form of ADHD or a subset of ME/CFS.)

From previous research, we know that ME/CFS and ADHD both involve neurotransmitter dysregulation that may involve serotonin, norepinephrine, and dopamine. However, that alone isn't enough to confirm more than a very loose relationship—neurotransmitters perform different jobs in different regions, and different jobs within a region based on specific receptors, so it's a complicated matter.

As we learn more about these conditions and their underlying mechanisms, we may grow to better understand the relationship.

Why Would the Same Drug Work for Both?

Back to these conditions appearing to be opposites now. Why would one medication help someone who's always exhausted and also someone who can't sit still?

Notice that the quote above talks about "psychostimulant medication." The key part of that phrase is "stimulant." For some reason, many stimulants have the opposite effect on people with ADHD than they have on others: They calm them down instead of speeding them up.

Other Research

This is an area of research that's drawn some on-going attention. Other studies have confirmed the link between ME/CFS and adult ADHD, especially in people who are also depressed. (It's likely not a coincidence that depression involves dysregulation of the same neurotransmitters.)

At least one study, published in Expert Review of Neurotherapeutics, helps shore up the evidence that methylphenidate (the drug in Ritalin) could have a promising role in ME/CFS treatment.

Should You Consider Ritalin for ME/CFS?

While research does suggest a connection, ADHD pharmaceuticals are not typically prescribed for chronic fatigue that's not caused by ME/CFS. Some doctors do prescribe ADHD medications off-label for ME/CFS, and these drugs work for some (but not all) people.

If you are experiencing difficulty with staying focused and attentive, and especially if you're depressed, this may be a medication to bring up with your doctor.