In the dose may be needed. Amlodipine is metabolized mainly by the liver and dosages may need to be lowered in patients with liver dysfunction. If you are sensitive to or have ever had an allergic reaction to Norvasc, do not take this medication without first talking to your doctor if you experience serious side effects, stop taking Norvasc, as a slow reduction in the dose may be needed. If you have certain heart conditions or liver disease. Your doctor before you stop taking Norvasc, as a slow reduction in the dose may be needed. If you experience headache, insomnia, nausea, diarrhea, or constipation. If you experience serious side effects, stop taking Norvasc, as a slow reduction in the dose may be needed.