Most common side effects:

• shortness of breath and/or chest tightness
• increase in blood pressure
• decrease in heart rate
• upper respiratory tract infection (common cold), including sore throat, stuffy or runny nose
• gastrointestinal symptoms, including nausea, diarrhea, and gas
• rash
• fatigue
• flu or flu-like symptoms
• irregular, abnormal, or painful periods (menses) and increase in the amount of menstrual bleeding

Various mutations of the cystic fibrosis gene block the "gates" that allow the flow of salt across the cell membranes. This causes mucus to become thick and clog the lungs. Lumacaftor is a "cystic fibrosis transmembrane conductance regulator (CFTC) corrector". The CFTR protein is a channel at the surface of the cells that allows the movement of particles such as chloride in and out of the cell, contributing to salt and water balance. Lumacaftor helps stabilize this CFTR protein channel.  The thick mucus is reduced and cystic fibrosis symptoms lessen. 

Use with caution if you:

• have kidney or liver problems
• have cataracts

Possible drug interactions: 

• ketoconazole, itraconazole, posaconazole, voriconazole, fluconazole​
• some antibiotics such as clarithromycin, erythromycin, rifampin, rifabutin
• phenobarbital, carbamazepine, phenytoin 
• midazolam, alprazolam, diazepam, triazolam 
• digoxin
• cyclosporine, tacrolimus 
• warfarin 
• St. John’s wort 

Use in pregnancy and breastfeeding.  Little is known about the safety of this medication when used in pregnancy and breastfeeding.  Consult your doctor or pharmacist before use.