What happens if a person misdiagnosed with adhd and having another(e.g. depression) take stimulants for the disease?

They don't get well: The main problem is likely to be that the person doesn't get well. Stimulants can have some beneficial effects on some kinds of depression, but are generally not nearly as effective as antidepressants.

Could be a problem: In some cases, either nothing will happen or there will be some remission of depression symptoms. In fact sometimes stimulants can be used with antidepressants in patients who have severe depression and trouble "getting going." however, if you have a cyclic mood disorder like bipolar disorder, stimulants could cause mania which could be a serious problem.

Incomplete treatment: If someone has been misdiagnosed and therefore not treated with the appropriate medication, your condition could worsen. Certainly at the least you may not see much improvement in symptoms. Since depression sometimes includes symptoms of poor concentration, feeling like you are partially treated may be possible. Often careful psychological testing is necessary to distinguish one from the other.

Depression not solve: Stimulants have many side effects which may contribute to the depression in some individuals and make symptoms like irritablity worse. However, they may also help the depressed individual feel more energetic and better able to focus. The main problem occurs if treating adhd leads to inadequate treatment of the depression or other condition.

Comorbidity : Depression is comorbid with adhd in the majority of adult cases. The amer acad peds published standards of care that delineate steps to be taken to determine if comorbidities are present before treating adhd. If so then the comorbidity is usually treated first since add meds can worsen anxiety, depression, ocd, bipolar disorder.