The following side effects may get better over time as your body gets used to the medication. Let your healthcare provider know immediately if you continue to experience these symptoms or if they worsen over time.
Common Side Effects
- Low blood sugar
- Reactions where the medication is injected (e.g., redness, swelling, itching)
Less Common Side Effects
- Fat deposits under the skin or pitting of the skin where the medication is injected
- Weight gain
- Swelling (e.g., in the legs, ankles, or feet)
Humulin R serious side effects
Contact your healthcare provider immediately if you experience any of the following.
- Severely low blood sugar: dizziness, shakiness, feeling confused, feeling irritable or anxious, feeling faint, sweating, extreme hunger, can't think clearly
- Dangerously low potassium levels: weakness, muscle cramps or twitches, constipation, abnormal heartbeat, tiredness, trouble breathing
- Severe allergic reaction: rash; hives; swelling of face, tongue, and throat; trouble breathing
Source: DailyMed
More on Humulin R side effects

The following Humulin R side effects have also been reported
Along with its needed effects, a medicine 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:
Incidence not known
blurred vision
chills
cold sweats
confusion
convulsions
cool, pale skin
decreased urine
difficulty with swallowing
dizziness
fast heartbeat
flushing or redness of the skin
headache
increased hunger
increased thirst
irregular heartbeat
loss of appetite
muscle pain or cramps
nightmares
numbness or tingling in the hands, feet, or lips
puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue
seizures
shakiness
slurred speech
sweating
swelling
tightness in the chest
unusual tiredness or weakness
unusually warm skin
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:
Incidence not known
Bleeding, blistering, burning, coldness, discoloration of the skin, feeling of pressure, hives, infection, inflammation, itching, lumps, numbness, pain, rash, redness, scarring, soreness, stinging, swelling, tenderness, tingling, ulceration, or warmth at the injection site
redistribution or accumulation of body fat
Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.
Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.
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