The side effects of Entecavir should be stated on the label for the medication or supplied by the pharmacy. I copy information I find on the Internet:
Some side effects of entecavir may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.
For the Consumer
Applies to entecavir: oral solution, oral tablet
Along with its needed effects, entecavir may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.
Check with your doctor immediately if any of the following side effects occur while taking entecavir:
Incidence not known
Abdominal or stomach discomfort
decreased appetite
diarrhea
fast, shallow breathing
general feeling of discomfort
muscle pain or cramping
nausea
rash
right upper abdominal or stomach pain and fullness
shortness of breath
sleepiness
unusual tiredness or weakness
Some side effects of entecavir 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:
Less common
Headache
Rare
Acid or sour stomach
belching
dizziness
heartburn
indigestion
sleepiness or unusual drowsiness
sleeplessness
stomach discomfort, upset, or pain
trouble sleeping
vomiting