What the label lists and what reports show
Clemastine side effects
Clemastine's FDA label: “Transient drowsiness, the most common adverse reaction associated with clemastine fumarate, occurs relatively frequently and may require discontinuation of therapy in some instances.” FAERS holds 1,357 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 dyspnoea (108 reports).
- Generic listed
Check it at the source: the clemastine FDA label on DailyMed (effective February 3, 2025, Genus Lifesciences); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsTransient drowsiness, the most common adverse reaction associated with clemastine fumarate, occurs relatively frequently and may require discontinuation of therapy in some instances.
From the label: adverse reactions, continuedTransient drowsiness, the most common adverse reaction associated with clemastine fumarate, occurs relatively frequently and may require discontinuation of therapy in some instances. Antihistaminic Compounds It should be noted that the following reactions have occurred with one or more antihistamines and, therefore, should be kept in mind when prescribing drugs belonging to this class, including clemastine. The most frequent adverse reactions are italicized. General: Urticaria, drug rash, anaphylactic shock, photosensitivity, excessive perspiration, chills, dryness of the mouth, nose, and throat. Cardiovascular System: Hypotension, headache, palpitations, tachycardia, extrasystoles. Hematologic System: Hemolytic anemia, thrombocytopenia, agranulocytosis. Nervous System: Sedation, sleepiness, dizziness, disturbed coordination, fatigue, confusion, restlessness, excitation, nervousness, tremor, irritability, insomnia, euphoria, paresthesias, blurred vision, diplopia, vertigo, tinnitus, acute labyrinthitis, hysteria, neuritis, convulsions. GI System: Epigastric distress, anorexia, nausea, vomiting, diarrhea, constipation. GU System: Urinary frequency, difficult urination, urinary retention, early menses. Respiratory System: Thickening of bronchial secretions, tightness of chest and wheezing, nasal stuffiness.
Source: FDA drug label, Genus Lifesciences, effective February 3, 2025 (SPL set cf8a3449-8bb3-4d5c-8d0d-557590e49ee5), via openFDA; the full label on DailyMed
What do FAERS reports show?
1,357 reports list clemastine among the medicines taken, each a report of something that happened, not proof the medicine caused it; 174 are coded as a death and 763 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 23 reactions below, 8 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?
- Clemastine: 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