Hi Thanks for posting your query on HCM. I appreciate your concern towards the safety of Methadone. Indeed Methadone can cause constipation. Treatment options: Change in lifestyles: Increasing dietary fiber & fluid intake Increasing exercise or physical activity Increasing time & privacy for toileting Laxatives like Lactulose, Bisacodyl or Liquid paraffin can be effective given either orally or in the form of rectal suppositories. Some time a combination of life style modification and laxative is required. The specific drug Methylnaltrexone helps restore bowel function in patients who have advanced illness and receive opioids for pain relief. You are advised to visit your doctor for the prescription of the above drugs. Hope your query is being answered. Kindly give your feedback if convinced. Best regards.