Bisphosphonates are a class of drugs that prevent the loss of bone mass, used to treat osteoporosis and similar diseases.
The cause for use of bisphosphonates is to treat diseases like osteoporosis and other conditions involving fragile, breakable bone.
Treatment with clear aligners for patients using bisphosphonates probably won't be able to move forward, since these types of drugs hinder osteoclastic activity, which is a crucial part of clear aligner therapy. This is also true for traditional orthodontics; if bone is unable to be broken down, then the teeth are just not going to move.
If you discover they are taking bisphosphonates, a choice will have to be made. If the patient cannot take a break from his or her bisphosphonates, then treatment will likely have to be discontinued or put on hold until the patient can stop taking them.