Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. Please be informed that I have read several studies on liver failure occurring with the use of hydroxycut in patients NOT on methadone. So, without even considering the variable of being on Methadone, which, by itself can stress the heart, taking hydroxycut can obviously be dangerous for some individuals. Hydroxycut is not just one product, but a variety of products and is not standardized as a content. I understand your concern about this rapid weight gain and am hoping you have had yourself checked by the doctor for your blood pressure, for fluid retention, your heart checked (rhythm, etc.) and had some general tests run including a TSH for your thyroid. Physical fitness is necessary before starting out on a nutritional plan to lose weight, particularly since an exercise component is key to the weight loss success. Also key to success is a healthy heart with a healthy kidney and thyroid. Circulatory problems may cause lower ankle swelling, elevated blood pressure and heart issues, so I do encourage you to have your overall health status checked. Now, on to some suggestions for the water retention. You may try limiting your sodium intake to 1,500 mg/day. A low-sodium diet may be obtained from a registered dietitian. Essentially, read labels, stay away from processed foods, obviously salty tasting foods, salt shaker on table, pickles, food additives such as MSG (monosodium glutamate) but remember to remain hydrated on 8 cups of water per day as dehydration may cause water retention as well. And, believe it or not, sugary foods cause a great deal of water to build up. Cut out added sugar and avoid fructose with the exception of 2 fresh fruits/day. Weight loss is best achieved, and this is backed up by evidence, through the combination of calorie restriction with a balanced diet, gradually increasing fiber to 25 g per day, exercise with a combination of both cardio and strength training, and last, but not least, cognitive therapy. Weight loss aides may be added in some cases to facilitate motivation and to counteract the weight gaining effects of some medicines. To recommend any particular one to you is unethical without doing a complete assessment of your medicines, health history, cardiac clearance, and motivation to make serious lifestyle changes. Consulting with a registered dietitian may help you sort all of these issues. So, first I suggest you to visit your physician and get an exercise clearance and then visit a registered dietitian with any labs you have and a 3 day food diary and work with him/her to set up a lifestyle plan to take that weight off you and help you improve your health. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Kathy Shattler