Radiotherapy is undeniably a treatment method that helps many patients struggling with cancer, but on the other hand, it can have some side effects. One possible side effect is cognitive impairment, which can appear after a certain period of time in patients who have undergone radiotherapy for an intracranial tumour as a child. However, researchers at the Swedish Karolinska Institutet report that a drug that has been known for years could offset the severity of these problems - lithium .