Oral contraceptives progestogen-only

Chambers DM, Jefferson GC, Chambers M, Loudon NB. Antipyrine elimination in saliva after low-dose combined or progestogen-only oral contraceptive steroids. Br J Clin Pharmacol 1982 13(2) 229-32. 

Information is limited, but it appears that these retinoids do not usually alter the efficacy of combined oral contraceptives. The one available case suggests that acitretin reduces the efficacy of progestogen-only oral contraceptives. However, note that progesto n-onty oral contraceptives do not reliably suppress ovulation in all cycles, and that this is not considered their primary mechanism of action (see Hormonal contraceptives and Sex hormones , (p.975)). The single report cannot therefore be taken as evidence that acitretin reduces the efficacy of progestogen-only contraceptives. 

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