Acetazolamide |
Antagonism of diuretic effect |
Amiloride |
Antagonism of diuretic effect |
Amitriptyline |
Antagonism of antidepressant effect but adverse effects increased due to increased plasma concentration of amitriptyline |
Amoxycillin |
Reduced contraceptive effect of estrogen-containing preparations |
Ampicillin |
Reduced contraceptive effect of estrogen-containing preparations |
Atenolol |
Antagonism of hypotensive effect |
Carbamazepine |
Accelerated metabolism of medroxyprogesterone (does not apply to injectable medroxyprogesterone acetate for contraception); reduced contraceptive effect (does not apply to injectable norethisterone enantate for contraception) |
Ceftazidime |
Reduced contraceptive effect of estrogen-containing preparations |
Ceftriaxone |
Reduced contraceptive effect of estrogen-containing preparations |
Cefuroxime |
Reduced effect of contraceptives |
Corticosteroids |
Oral contraceptives increase plasma concentration of corticosteroids |
Clomipramine |
Antagonism of antidepressant effect but adverse effects increased due to increased plasma concentration of clomipramine |
Cyclosporine |
Inhibition of cyclosporine metabolism (increased plasma–cyclosporine concentration) |
Doxycycline |
Reduced contraceptive effect of estrogen-containing preparations |
Efavirenz |
Efficacy of oral contraceptives reduced |
Enalapril |
Antagonism of hypotensive effect |
Fluconazole |
Anecdotal reports of contraceptive failure |
Fosphenytoin |
Reduced contraceptive effect |
Furosemide |
Antagonism of diuretic effect |
Glibenclamide |
Antagonism of hypoglycaemic effect |
Glimepiride |
Reduced hypoglycaemic action |
Glucagon |
Antagonism of hypotensive effect |
Glyceryl trinitrate |
Antagonism of hypotensive effect |
Griseofulvin |
Reduced contraceptive effect of levonorgestrel, accelerated metabolism of medroxyprogesterone (does not apply to injectable medroxyprogesterone acetate for contraception); does not apply to injectable norethisterone enantate for contraception |
Hydralazine |
Antagonism of hypotensive effect |
Hydrochlorothiazide |
Antagonism of diuretic effect |
Insulins |
Antagonism of hypoglycaemic effect |
Isosorbide dinitrate |
Antagonism of hypotensive effect |
Metformin |
Antagonism of hypoglycaemic effect |
Methyldopa |
Antagonism of hypotensive effect |
Nelfinavir |
Accelerated metabolism of levonorgestrel, medroxyprogesterone and norethisterone (reduced contraceptive effect); does not apply to injectable medroxyprogestrone acetate for contraception |
Nevirapine |
Accelerated metabolism of levonorgestrel, medroxyprogesterone and norethisterone (reduced contraceptive effect); does not apply to injectable medroxyprogestrone acetate for contraception |
Nifedipine |
Antagonism of hypotensive effect |
Phenobarbital |
Metabolism accelerated (reduced contraceptive effect); does not apply to injectable medroxyprogestrone acetate for contraception; does not apply to injectable norethisterone enantate for contraception |
Phenytoin |
Accelerated metabolism of levonorgestrel, norethisterone (reduced contraceptive effect); does not apply to injectable medroxyprogestrone acetate for contraception; does not apply to injectable norethisterone enantate for contraception |
Propranolol |
Antagonism of hypotensive effect |
Rifampicin |
Accelerated metabolism of levonorgestrol and medroxyprogesterone (reduced contraceptive effect); does not apply to injectable medroxyprogestrone acetate for contraception; does not apply to injectable norethisterone enantate for contraception |
Ritonavir |
Accelerated metabolism of levonorgestrol and norethisterone (reduced contraceptive effect); does not apply to injectable medroxyprogestrone acetate for contraception; does not apply to injectable norethisterone enantate for contraception |
Sodium nitroprusside |
Antagonism of hypotensive effect |
Spironolactone |
Antagonism of diuretic effect |
Topiramate |
Failure of contraceptive effect |
Theophylline |
Delayed excretion of theophylline; increased plasma concentration |
Verapamil |
Antagonism of hypotensive effect |
Warfarin |
Antagonism of anticoagulant effect |