Common Nausea, Lightheadedness, Slow heart rate, Headache, Breathlessness, Dizziness, Flushing (sense of warmth in the face, ears, neck and trunk), Chest tightness, Burning sensation.

Expert advice for Carnosine Injection

Inform your doctor if you have any of the following heart problems: heart attack/ failure, or heart transplant within the last year; unusual heart rhythm (atrial fibrillation or flutter), low blood volume/ narrowing of heart valves.
Consult your doctor if you have narrowing of the main arteries in your neck (carotid arteries).
Take precautions while taking adenosine if you have recurrent fits.
Caution must be exercised if you have had recurrent fits or experienced difficulty in breathing and problems associated with blood pressure, urination, defecation, etc.
You may need to monitor your condition (ECG and blood pressure) while taking adenosine.
Avoid food or drinks that have caffeine before taking this drug. 
Tell your doctor if you are or planning to become pregnant or are breastfeeding.

Q. Is adenosine a hormone/an amino acid/nucleotides/beta blocker/calcium channel blocker?
Adenosine belongs to class of drugs called nucleosides. It acts by restoring the heart rhythm. It also relaxes blood vessels supplying the heart and increases blood flow, thereby relieving abnormal electrical activity due to compromised blood flow to heart

Q. Is Carnosine a vasopressor/does Carnosine cause vasodilation/ vasoconstriction/ bronchoconstriction?
Carnosine causes vasodilatation which may result in headache, dizziness, lightheadedness, tachycardia and flushing. It also causes bronchoconstriction resulting in breathlessness and chest discomfort

Q. Does Carnosine makes you sleepy?
No. Carnosine has no effect on sleep

Q. Does Carnosine cause atrial fibrillation?
Yes, Carnosine can cause various types of disturbances in heart rhythm; atrial fibrillation is one of them.