Check with your doctor immediately if any of the following side effects occur:

Less common or rare
Less common or rare with azatadine, cetirizine, clemastine, cyproheptadine, desloratadine, dexchlorpheniramine, diphenhydramine, or loratadine

Abdominal or stomach pain
burning
chills
clay-colored stools or dark urine
cough
diarrhea
difficulty swallowing
dizziness
fast or irregular heartbeat
fever
headache
hives
itching
prickly sensations
puffiness or swelling of the eyelids or around the eyes, face, lips or tongue
redness of skin
seizures
shortness of breath
skin rash
swelling
tightness in chest
tingling
unusual tiredness or weakness
wheezing
Check with your doctor as soon as possible if any of the following side effects occur:

Less common or rare
Sore throat
unusual bleeding or bruising
unusual tiredness or weakness
Symptoms of overdose
Clumsiness or unsteadiness
convulsions (seizures)
drowsiness (severe)
dryness of mouth, nose, or throat (severe)
feeling faint
flushing or redness of face
hallucinations (seeing, hearing, or feeling things that are not there)
shortness of breath or troubled breathing
trouble in sleeping
Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common
Drowsiness
dry mouth, nose, or throat
gastrointestinal upset, stomach pain, or nausea
headache
increased appetite and weight gain
thickening of mucus
Less common or rare
Acid or sour stomach
belching
blurred vision or any change in vision
body aches or pain
clumsiness or unsteadiness
confusion (not with diphenhydramine)
congestion
constipation
cough
diarrhea
difficult or painful urination
difficulty in moving
difficult or painful menstruation
dizziness (not with brompheniramine or hydroxyzine)
drowsiness (with high doses of desloratadine and loratadine)
dryness of mouth, nose, or throat
early menstruation
fast heartbeat
fever
heartburn
hoarseness
increased sensitivity of skin to sun
increased sweating
indigestion
loss of appetite
joint pain
muscle aching or cramping
muscle pains or stiffness
nausea
nightmares (not with azatadine, chlorpheniramine, cyproheptadine, desloratadine, hydroxyzine, or loratadine)
ringing or buzzing in ears
runny nose
skin rash
swollen joints
stomach discomfort, upset or pain
tender swollen glands in neck
tremor
unusual excitement, nervousness, restlessness, or irritability
vomiting