Hi I had gone through the question and understand your concern. See , methadone is a powerful synthetic analgesic drug which is similar to morphine in its effects but less sedative and is used as a substitute drug in the treatment of morphine and heroin addiction. Side effects: Commonly these include dizziness, sleepiness, vomiting, and sweating. Serious risks include opioid abuse or a decreased effort to breathe. Heart arrhythmia(heart rate irregularity) may also occur. I hope this information helps. Let me know if you have any other queries. Thank you.