It is well acknowledged that the oral absorption of a drug can be influenced by its solubility, which is usually associated with its solid form properties. G1032 is a retinoic acid–related orphan receptor inverse agonist. Crystalline solid (form A) was identified with an aqueous solubility of 130 μg/mL. This form was used in an oral dose escalation study in rodents up to 300 mg/kg and achieved good exposures. Later on, a more stable crystalline hydrate (form B) was identified and the aqueous solubility was reduced to 55 μg/mL. A modeling exercise suggested that this solubility change would cause a 2-fold decrease in exposure at tested doses; however, the actual reduction was far larger than the model predicted. At high dose, exposure was found to be reduced by almost 10-fold. A parameter sensitivity analysis suggested that such a drop in exposure could be associated with permeability reduction as well. More in vitro permeability experiments were performed, indicating G1032 was an efflux transporter substrate. This finding was integrated into the modeling and the design for in vivo studies. Data obtained from those studies allowed us to better understand the causes of the higher-than-expected exposure change and enabled decision-making.