Death has other calculations

They find a woman named Noha sleeping on her bed dead, and next to her is a box of finished and open medicine. It turns out to be a suicide. During the autopsy, the forensic doctor discovers that there are no traces of the medicine in her stomach. He thinks that it is possible that she took the last pill of the medicine by chance and died, because there is no trace of a crime or suicide. Then the cleaner finds the pills in the trash and takes them to the police. Here they confirm that this is a murder. So, who did this and why?