To determine which of the listed drugs can cause hypothermia when ingested in toxic doses, we need to understand the effects of each drug on the body. Hypothermia refers to a body temperature that drops below normal levels.

1. Digoxin: Digoxin is a cardiac glycoside used to treat heart conditions. It primarily affects heart rate and contractility and does not characteristically cause hypothermia in cases of toxicity.
2. Chlorpromazine: Chlorpromazine is an antipsychotic medication that is known for causing temperature dysregulation because it affects the hypothalamus, the part of the brain responsible for thermoregulation. In cases of overdose, chlorpromazine can result in hypothermia due to this disturbance in temperature regulation.
3. Iron: Iron overdose can lead to metabolic acidosis and damage to the gastrointestinal tract but does not cause hypothermia.
4. Alcohol: Alcohol can cause hypothermia as it leads to peripheral vasodilation, increasing heat loss. However, among the given options, chlorpromazine is more directly associated with significant hypothermic effects due to its pharmacological action on the hypothalamus.

Based on the above reasoning, the drug that causes hypothermia in toxicity is Chlorpromazine.

Conclusion: Chlorpromazine affects the body's ability to regulate temperature, making hypothermia a potential side effect in cases of overdose.