Well I have to say that I have asthma and when I got pregnant with my first, my other half was on drugs......my oldest was and is very healthy:) Its very important to keep using your asthma meds. Your doctor will more than lilely tell you this too. I dont really know the importance of the father being on drugs.........Just do what you can to make your pregnancy healthy. I am sure you will be fine.
Have you mentioned to docs etc about the fact that the father uses drugs. My ex partner and the father of my child used them, i was equally as worried. I think its more harmful if its the mother herself who abuses the subtances to be honest. Your asthma shouldnt be a problem hun, not all things end up bein passed via the genes.
Im not a doc though hun, so why not make an appt to speak to someone who will more than likely put your mind at ease for you.Raise any concerns with them, thats what they are there for. Try not to worry too much, you dont wanna be getting stressed with your lil one relying on you to carry it healthily, so if its worrying you that much then please go get some answers. I was always ringing my midwife when i was pregnant with my little one