This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Substance Abuse, Subject name: Psychiatry
Symptom of opioid withdrawal is: 
Select and explain. 
A. Piloerection, B. Dry Skin, C. Bradycardia, D. Pupillary construction
A: Piloerection
Answer: A: Piloerection 
Explanation: Ans. A. PiloerectionOpioid Withdrawal* With long-term use of opioids down regulation of dynorphins, endogenous endorphins and opioid receptors takes place.* Abrupt cessation of opioid use does not allow time for upregulation of receptors It results in elevated neuronal firing and the opioid withdrawal syndrome.* Opioid withdrawal usually starts with-- Diaphoresis- Yawning- Feelings of anxiety- Lacrimation- Rhinorrhea and diffuses myalgias.It then progresses to -- Nausea- Profuse vomiting- Diarrhea, Piloerection, mydriasis and abdominal dehydration.* Opioid withdrawal reactions are not life-threatening and rarely fatal but they are very uncomfortable.* Vomiting and aspiration of gastric contents causes pneumonitis.