Which drug for alcohol abuse patients has not established safety in pregnancy?

Disulfiram is a medication used in the management of alcohol dependence, but it has not established safety in pregnancy. The lack of safety data is primarily due to its mechanism of action, which inhibits the enzyme acetaldehyde dehydrogenase, leading to unpleasant reactions when alcohol is consumed. This putative discomfort is intended as a deterrent to drinking but poses ethical and safety considerations during pregnancy, as it's unclear how it may affect fetal development.

In contrast, acamprosate is considered safer for use in pregnant individuals as it acts on the glutamate system and does not have known harmful effects on fetal development, although data are still limited. Varenicline is a smoking cessation aid, and while it has unclear safety in pregnancy as well, its primary indication is not alcohol use. Bupropion, an antidepressant and smoking cessation aid, has also been deemed safer relative to disulfiram when it comes to pregnancy, although it should still be used with caution.

Thus, the concern with disulfiram is about its unknown effects on pregnancy and lack of established safety, making it the correct choice in this context.