What the label lists and what reports show
Dalfampridine side effects
Dalfampridine's FDA label: “The most common adverse events (incidence ≥2% and at a rate greater than the placebo rate) for AMPYRA were urinary tract infection, insomnia, dizziness, headache, nausea, asthenia, back pain, balance disorder, multiple sclerosis relapse, paresthesia …” FAERS holds 71,317 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is gait disturbance (10,976 reports).
- Generic listed
Check it at the source: the dalfampridine FDA label on DailyMed (effective January 16, 2026, Merz Pharmaceuticals, LLC); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What are the possible side effects of AMPYRA?AMPYRA may cause serious side effects, including: serious allergic reactions. Stop taking AMPYRA and call your doctor right away or get emergency medical help if you have: shortness of breath or trouble breathing swelling of your throat or tongue hives See "What is the most important information I should know about AMPYRA?" The most common side effects of AMPYRA include: urinary tract infection trouble sleeping (insomnia) dizziness headache nausea weakness back pain problems with balance multiple sclerosis relapse burning, tingling or itching of your skin irritation in your nose and throat constipation indigestion pain in your throat Tell your doctor if you have any side effect that bothers you or that does not go away. These are not all the possible side effects of AMPYRA. For more information, ask your doctor or pharmacist. Call your doctor for medical advice about side effects. […]
Source: FDA drug label, Merz Pharmaceuticals, LLC, effective January 16, 2026 (SPL set 550eb76a-e4a6-4fa1-ad65-c0fd8b0ce783), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsThe most common adverse events (incidence ≥2% and at a rate greater than the placebo rate) for AMPYRA were urinary tract infection, insomnia, dizziness, headache, nausea, asthenia, back pain, balance disorder, multiple sclerosis relapse, paresthesia, nasopharyngitis, constipation, dyspepsia, and pharyngolaryngeal pain ( 6.1 ).
Table 1: Adverse Reactions with an Incidence ≥2% of AMPYRA-Treated Adult MS Patients and More Frequent with AMPYRA Compared to Placebo in Controlled Clinical Trials
| Adverse Reaction | Placebo (N=238) % | AMPYRA 10 mg twice daily (N=400) % |
|---|---|---|
| Urinary tract infection | 8 | 12 |
| Insomnia | 4 | 9 |
| Dizziness | 4 | 7 |
| Headache | 4 | 7 |
| Nausea | 3 | 7 |
| Asthenia | 4 | 7 |
| Back pain | 2 | 5 |
| Balance disorder | 1 | 5 |
| Multiple sclerosis relapse | 3 | 4 |
| Paresthesia | 3 | 4 |
| Nasopharyngitis | 2 | 4 |
| Constipation | 2 | 3 |
| Dyspepsia | 1 | 2 |
| Pharyngolaryngeal pain | 1 | 2 |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
From the label: adverse reactions, continuedThe following serious adverse reactions are described in more detail elsewhere in the labeling: Seizures [see Warnings and Precautions (5.1) ] Anaphylaxis [see Warnings and Precautions (5.4) ] The most common adverse events (incidence ≥2% and at a rate greater than the placebo rate) for AMPYRA were urinary tract infection, insomnia, dizziness, headache, nausea, asthenia, back pain, balance disorder, multiple sclerosis relapse, paresthesia, nasopharyngitis, constipation, dyspepsia, and pharyngolaryngeal pain ( 6.1 ). To report SUSPECTED ADVERSE REACTIONS, contact Acorda Therapeutics at 1-800-367-5109 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trials Experience Because clinical studies are conducted under widely varying conditions, adverse reaction rates observed in the clinical studies of a drug cannot be directly compared to rates in the clinical studies of another drug and may not reflect the rates observed in practice. In three placebo-controlled clinical trials of up to 14 weeks duration, 4% (15/400) of patients treated with AMPYRA 10 mg twice daily experienced one or more adverse reactions leading to discontinuation, compared to 2% (5/238) of placebo-treated patients. …
Source: FDA drug label, Merz Pharmaceuticals, LLC, effective January 16, 2026 (SPL set 550eb76a-e4a6-4fa1-ad65-c0fd8b0ce783), via openFDA; the full label on DailyMed
What do FAERS reports show?
71,317 reports list dalfampridine among the medicines taken, each a report of something that happened, not proof the medicine caused it; 1,759 are coded as a death and 10,146 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Reports rose sharply in 2016 (12,012, against a median of 2,758 a year): FAERS counts follow reporting, which news, litigation and label changes can drive, not how often a reaction happens. Of the 21 reactions below, 9 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Dalfampridine: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions