Erlotinib is helpful for the treatment of lung cancer as it slows down the growth of cancer cells. There are some products that may interact with the drug are warfarin and some drugs that lower stomach acid. Remember that your doctor has prescribed this medication because he or she knows that the benefit to you is greater than the risk of side effects. There are some common side effects like diarrhea, weakness, cough, fatigue. Erlotinib Price vary according to various wholesalers and pharma brands.