In multiple sclerosis, the immune system attacks the myelin sheaths that protect nerve cells
The ADHD medication is not a universal cognitive enhancer
STUDY: Morrow SA et al, Mult Scler Relat Disord 2026
STUDY TYPE: Randomized controlled trial
FUNDING: MS Canada
Background
Slowed thinking is common in multiple sclerosis (MS) and the leading cause of work disability. This larger trial follows up on a smaller one that found positive results with mixed amphetamine salts (Adderall XR).
The Study
- 123 adults with MS and slowed processing speed on the Symbol Digit Modalities Test (SDMT), randomized to Adderall XR 10 mg, 20 mg, or placebo for 12 weeks; 109 completed.
- Primary outcome was SDMT change.
Results
All three groups gained 5 to 7 points on the SDMT, with no difference between drug and placebo.
On secondary outcomes: no difference on memory tests, but the 20 mg group reported less cognitive fatigue on the Fatigue scale (MFIS), improving 9.3 points versus 5.0 on placebo. With so many outcomes tested, this may be chance.
Side Effects
Seven patients on Adderall dropped out for side effects, mostly insomnia and weight loss, compared with none on placebo. Insomnia affected 6 of 34 patients on 20 mg.
Limitations
- Smaller than planned 150 patients, though the results weren’t close to significance.
- The 20 mg group was younger.
- Patients with ADHD or major depression were excluded.
Practice Implications
- Amphetamines carry risks and are not robustly effective for fatigue or cognition in populations outside of ADHD.
—Chris Aiken, MD
Director, Psych Partners
Editor in Chief, Carlat Psychiatry Report
