Constipation may occur for one of several reasons, including:
the reptile is dehydrated;
the reptile is impacted with fur, chitin, or particulate substrate, including commercial"lizard" and "reptile" substrates, or other foreign material or object;
the enclosure is too cool;
the basking temperatures needed are not being provided;
the reptile is suffering from a severe parasite infection;
the reptile is partially paralyzed from an injury or nutritional disorder.
As with all animals, ridding the body of wastes is essential for overall health. If wastes, either urates or feces, are lodged in the body, systemic infections and organ failure will eventually occur.
Being constipated is also uncomfortable, if not actually painful, for the reptile. This can lead to behavioral abnormalities, such as a reptile who is usually comfortable being handled becomes thrashy and irritable when handled, or a formerly active reptile becomes sluggish.
If the reason for the constipation cannot be determined, the reptile must be seen by a reptile vet for examination and, if necessary, x-rays to determine if there is an object lodged anywhere in the gut.
While you are searching for the reason for the constipation, you must assist the reptile to defecate. Bathe him in warmish water in the bath tub. After letting him soak for 10-15 minutes, begin to gently massage his belly, stroking from sternum to vent, for 5-10 minutes, rewarming the water as needed. This will usually get them to poop within 24 hours. If the reptile doesn't defecate by then, get it to a reptile vet ASAP.
Reptiles, especially lizards who are partially paralyzed due to metabolic bone disease, will have to be bathed and massaged daily to make sure they are able to void all their wastes.
Do not attempt to administer laxatives or enemas yourself. Many products may be fatal, and reptiles may take a significantly lower dose than a mammal or bird. This should only be done in consultation with your reptile veterinarian.