Drugs which have potential to effect the efficacy of hormonal contraception

Example drugs are listed. Please check guidance (1) and BNF for more comprehensive information.

• drugs that reduce contraceptive hormone levels or decrease contraceptive effects are
  
  
  • antiepileptics e.g. - carbamazepine, phenobarbital, phenytoin
    • modest to marked reduction in ethinylestradiol (EE) and progestogens. Possible reduced contraceptive efficacy
      
      
  • antibiotics e.g. - rifabutin, rifampicin
    • rifabutin associated with a modest reduction in EE or estradiol and progestogen. Rifampicin has a marked effect
      
      
  • antiretroviral e.g. - ritonavir - marked reduction in EE. EE reduced by 40%. Additional and/or alternative contraceptive methods advised
    
    
  • emergencey contraceptives e.g - ulipristal acetate
    • theoretical reduction in the efficacy of progestogen-containing contraceptives. Additional precautions required for 14 days (9 days if using or starting POP, 16 days for Qlaira®)
      
      
  • gastrointestinal drugs e.g. - proton pump inhibitors, antacids, H2 receptor antagonists
    • theoretical reduction in plasma concentrations of UPA and may result in decreased efficacy. Concomitant use not recommended
      
      
  • herbal e.g. - St. Johns Wort - is a weak enzyme inducer and has the potential to reduce efficacy
    
    
• drugs that increase contraceptive hormone levels
  • antibacterial e.g. - erythromycin
    
    
• the clinical significance is not known but increased adverse events might be anticipated
  • antifungal e.g. - fluconazole, itraconazole, ketoconazole
    
    
• modest increases in EE and progestogen
  • antiretroviral e.g. - atazanavir
  • NSAID's e.g. - etoricoxib
    • doses of etoricoxib >=60 mg raise ethinylestradiol (EE) levels by approximately 40% or more
      
      
• potential risk of estrogen-related adverse events
• statins e.g - atorvastatin the clinical significance is not known but likely to be small

Reference

• 1. Royal College of Obstetricians and Gynaecologists. Faculty of Sexual and Reproductive Healthcare guideline 2011. Drug Interactions with Hormonal Contraceptions