No period, equals no pregnancy?????

Patient: I’ve searched the Internet for an answer to my question and haven’t had any luck, so I’m hoping I can get an answer here; from a medical professional. Here is the question: Many female heroin addicts experience cessation of their menstrual cycle while using, but does this also mean their ovulation stops? Thus, their ability to conceive is compromised?? I’m aware that not all female users’ periods cessate and that some heroine addicts can and have become pregnant. That’s not my question. I want to know if someone, who is not having a period, can become pregnant while the bleeding is absent. Please help! Thank you!