What the label lists and what reports show
Dantrolene side effects
Dantrolene's FDA label lists its adverse reactions in its own words. FAERS holds 1,745 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 neuroleptic malignant syndrome (172 reports).
- Generic listed
- Boxed warning
Check it at the source: the dantrolene FDA label on DailyMed (effective August 21, 2026, Par Health USA, LLC); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsThe most frequently occurring side effects of dantrolene sodium have been drowsiness, dizziness, weakness, general malaise, fatigue, and diarrhea. These are generally transient, occurring early in treatment, and can often be obviated by beginning with a low dose and increasing dosage gradually until an optimal regimen is established. Diarrhea may be severe and may necessitate temporary withdrawal of dantrolene sodium therapy. If diarrhea recurs upon readministration of dantrolene sodium, therapy should probably be withdrawn permanently. Other less frequent side effects, listed according to system, are: Gastrointestinal: Constipation, rarely progressing to signs of intestinal obstruction, GI bleeding, anorexia, swallowing difficulty, gastric irritation, abdominal cramps, nausea and/or vomiting. Hepatobiliary: Hepatitis (see WARNINGS ). …
Table 1: Adverse Events in Healthy Volunteers
This table is printed in the RYANODEX dantrolene sodium label published by Eagle Pharmaceuticals, Inc. of October 30, 2024; the label quoted above does not print one.
| Reaction | RYANODEX [N=30] n (%) | Dantrolene Sodium Comparator [N=31] n (%) |
|---|---|---|
| Flushing | 8 (27) | 1 (3) |
| Somnolence | 5 (17) | 4 (13) |
| Dysphonia | 4 (13) | 1 (3) |
| Dysphagia | 3 (10) | 4 (13) |
| Nausea | 3 (10) | 3 (10) |
| Feeling abnormal | 3 (10) | 3 (10) |
| Headache | 1 (3) | 4 (13) |
| Vomiting | 1 (3) | 2 (6) |
| Vision blurred | 1 (3) | 1 (3) |
| Pain in extremity | 1 (3) | 1 (3) |
| Muscular weakness/Asthenia | 1 (3) | 1 (3) |
| Atrioventricular block | 1 (3) | 0 |
| Tachycardia | 1 (3) | 0 |
| Infusion site pain | 1 (3) | 0 |
| Dizziness | 1 (3) | 0 |
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.
Source: FDA drug label, Par Health USA, LLC, effective August 21, 2026 (SPL set 11689f56-15e0-4350-b53f-ae96e5994fea), via openFDA; the full label on DailyMed
What do FAERS reports show?
1,745 reports list dantrolene among the medicines taken, each a report of something that happened, not proof the medicine caused it; 198 are coded as a death and 854 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. Of the 21 reactions below, 7 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?
- Dantrolene: 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