Final answer:
The effectiveness of oral contraceptives can be decreased by smoking, which impacts fertility and alters hormone metabolism, and by the use of certain antibiotics that increase the metabolism of contraceptive hormones. The correct option is a) Smoking and antibiotic use
Step-by-step explanation:
Two factors that decrease the effectiveness of oral contraceptives are a) Smoking and antibiotic use. Smoking can have a detrimental impact on fertility and can also affect the metabolism of contraceptive hormones in the body, which may lower the effectiveness of the pill.
Antibiotic use, particularly with drugs such as rifampin, can decrease the efficacy of oral contraceptives by enhancing the metabolic rate of contraceptive hormones, ultimately leading to a reduced concentration of these hormones in the bloodstream and increasing the risk of unintended pregnancy. The correct option is a) Smoking and antibiotic use