Yes, you can take Ali with synthroid; my doctor actually prescribe xenical (same drug in Ali, but stronger), but I never got the script filled because insurance doesn't pay and it was $300+/month. Just make sure you leave a separation of a few hours between them.
I would advise that you think twice about trying it, though, because if you don't eat properly, the "side effects" can be brutal. The worst thing about Ali is that it can't distinguish between the good fats and the bad ones, so you may miss out on some essential nutrients.
You should discuss the use of Ali with your doctor.
Best way to lose weight is to implement a healthy diet, and moderate exercise program. Some of us just have to work a lot harder at it than others. I'm right there with you.
I would advise you to trya and enter your Diet medication and your thyroid meds at a web-site such as "Drugs.com, they have a good Interactions Checker, and the site is free. We do not have a Data Base to check interactions with all medications. Best Wishes FTB4