The correct answer is B. 1 month.

Isotretinoin is a synthetic retinoid that is used primarily in the treatment of acne. Isotretinoin has a half-life of approximately 20 hours. Women should be advised to avoid becoming pregnant for at least one month.

The other listed time frames are not correct.

References:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2835909/

Brought to you by our brand partner