What are the disadvantages to taking fertility medicaitions?

Multiples, Costs. Every medication has benefits and risks. You question the risks: costs are variable from a few hundred to few thousand; multiple births vary but perhaps biggest concern; hyperstimulation syndrome and usual miscellaneous and allergies. Don't forget the benefit of getting pregnant. Modern infertility care depends heavily on medication. Meds safe is used properly and prudently. Best wishes.
At 42: no many. Risk of ovarian hyper stimulation at 42 is negligible. Risk of multiple pregnancy is real with ivf, but honestly at 42 the main risk is of wasting time using 1) oral fertility drugs and 2) injectable fertility drugs for anything short of ivf (e.g. Intrauterine inseminations). Infertility at 42 is a reproductive emergency: seek ultra-qualified advice by a certified reproductive endocrinologist.