If your family member is actively involved in their addiction you can still have a "healthy" relationship with them but it will look and feel a lot different than a normal healthy relationship.
You can't have a normal healthy relationship with someone who is actively using drugs.
What is different? Number one you should not trust them. Not trusting them even if you want to is a good thing because it is a sign that you are understanding the reality of their situation. It is also important to develop a non judgmental understanding of your loved one's condition this is an important step in having a healthy relationship. Non judgmental does not mean you like what is going on but does mean you understand what is going on, and are willing to avoid falling into a power struggle with your loved one.
You need to be very consistent in your communication with the addicted person and avoid trying to manipulate them like the plague. It is important to learn how to take back your life while you reduce your urge to manipulate them manage their life while your life falls apart.
People that care about the addicted person tend to get scared, or angry when they can't make something positive happen. When family members don't get support their relationship with the addict becomes driven by anxiety and is focused on trying to make something happen to change the situation. This sets up a power struggle and the addicted person starts focusing on you as the problem and you are focused on trying to manage their life while your life starts to disappear.
It is important for you focus on maintaining the quality of your life and give consistent messages to the addicted person in your family. The messages should be that you love them and you want them to get help for their addiction and you will hold them accountable for their behavior. Without the drama of a power struggle there is no resentment and anger that gets in the way of communication. This leaves an opening for the future when they are struggling and start to believe they do need help for them to talk with you.