Unless a therapy is compared to something else, it is not possible to know what would happen without it.
If people get better or worse after a treatment, you are comparing how they were after the treatment to how they were before it. The problem with such “before and after” comparisons is that you don’t know what would have happened without the treatment.
For example, if a group of people with mild dysarthria following acute stroke chewed gum and their speech improved it might seem like the gum chewing helped. However, their dysarthria probably would have got better without the gum chewing. The best way to find out if the gum chewing made a difference would be to compare one group of people with mild dysarthria following acute stroke who chewed gum to another group with mild dysarthria following acute stroke that did not – and to make sure that it was a fair comparison.
BEWARE of treatment claims when you don’t know what the comparison was, and when they are based on before and after comparisons only.