You can stop taking a pill or an injection treatment, but you can’t stop or retract stem cell treatments if there’s a bad side effect.
Unlike other kinds of medicines, once stem cells have been transplanted into patients, if something goes wrong you cannot stop the ‘treatment’. There’s no retraction possible because transplanted stem cells spread in the body and potentially integrate.
One of the striking things in the commercial stem cell arena in 2016 was the emergence of patient lawsuits against stem cell clinics including two proposed class action suits. These patients, and I count potentially now more than a dozen, allege a variety of harms ranging from tumors to blindness. The reason I mention this is that there appears to be huge potential for harm to patients from unapproved stem cell therapies. I know a lot of patients who would wish they could undo what the stem cell clinic did. It’s just not possible.
Even in an appropriately regulated stem cell trial context, there’s no easy way to undo stem cell transplants. There has been talk for years about suicide genes to be inserted into stem cells to provide “a net” should something go awry with stem cell treatments, but it’s not clear how well these would work and stem cell clinics aren’t interested in that anyway.