This is a problem popping up mostly in wintertime, but sometimes also at other periods of the year. Tegus show very easy when there is a problem by stop acting like they normally do. Here is a checklist about the things that could be wrong.

• Check the temperatures in your enclosure. Too low temperatures can the engine of your tegu. They can not digest food anymore so they will have big trouble eating too. The hotspot must be around 45/55C (113/131F) and the cold corner 25/30C (77/86F). At night not under 23C (73F). Also check if your terrarium is not standing directly on the floor. If you heat your enclosure air temperature and the floor gives a lot of cold.. its posible it makes your soil very cold. Tegus hide under the soil get a body temperature that is too cold. You can put some wood blocks or insulation under the enclosure to keep the cold away. Also the room temperature can have small influence in the temperature in the enclosure.

• Parasites can also stop a tegu from eating. They can get parasites in many different ways. They get it from other animals, your hands, stress, raw food (check your food sorce). Most of the time tegus can fight of small amounts of parasites. But when they get stressed, with moving or just an immumesystem that is not that good at that moment can make the parasites multiply. If the enclosure its climate is perfect you can do a parasite test. This test you can get done by collecting fresh poop and bring it to a vet. A normal cat dog vet can even do the check. When it has parasite I always recommend to use Iverquantel (0,5ml a kilo at day 1 and day 10) or Flagyl (1,25ml a kilo 5 days, 1 time a day) depending on what parasite it is. My experiance with panacur on reptiles, especially tegus is really bad. So i recommend to never use that. Always ask a vet what medicine is best to be used. Never try yourself.
  
• If it’s not parasites go to a vet and ask for bacterial infection swab to see if it carries a bacterial infection. This can also make them really sick.