I had one Sim who would take drugs often but was never addicted. Well she had her first miscarriage, I understood it to be a reaction to her drug use, I stopped her from taking drugs, even stopped her husband from taking any, but she kept having miscarriage after miscarriage. It was very frustrating.
I ended up just deleting her and letting her husband remarry. Even when his drug use started back up again, his wife was still able to get pregnant. Idk if there's something in the code or whatever that says if a woman has ever taken drugs she cannot get pregnant successfully or what, but that seemed to be the case for me. Or was it a glitch? Idk.