Lasix (furosemide) is a loop diuretic (a water pill) prescribed for the treatment of fluid retention diagnosed with a wide variety of health conditions. Your health care provider needs to know about any disease you have been diagnosed with to be able to prescribe the right dosage. Make sure you mention any of the following ones: gout, diabetes, lupus, kidney or liver disease, allergy to any sulfa drugs. Lasix has been classified as FDA pregnancy category C - it is not known whether this drug can affect the health of an unborn baby, but it is known that Lasix passes into breast milk and can do harm to the nursing infant. If you are pregnant or breastfeeding you might want to discuss your situation with a qualified professional to make sure your baby is completely safe. If you took Lasix in spite of the fact you already had an allergic reaction to it the following symptoms may be developed: swelling of your lips, face, throat and tongue, hives, trouble breathing and skin rash. Some of the side effects you may have when using this drug include but are not limited to constipation, diarrhea, headache, dizziness, tingling, blurred vision, stomach pain and numbness. More serious side effects that you should immediately report to your health care provider include weakness, lightheadedness, drowsiness, peeling skin rash, muscle pain, loss of appetite, clay-colored stools and dark urine, easy bleeding and bruising, restlessness, fast heartbeat, urinating less than usual and yellowing of your skin (jaundice).