In some instances, it may be safe to quit using a substance without medical intervention, but that is best determined by a doctor or medical professional.
In some cases, substances (such as benzodiazepines or alcohol) can cause life-threatening side effects during the withdrawal phase. These dangerous effects may also not occur right away, so they can catch you or your loved one off-guard.
It is best to speak with a doctor or other healthcare provider about your substance abuse and let them determine whether it is safe for you to discontinue use without medical supervision.