**Question:** For which of the following drugs a warning is written 'To be sold by retail on the prescription of a Registered Medical Practitioner only'

A. Pethidine
B. Bromocriptine
C. Quinine
D. Phenobarbitone

**Core Concept:** The question is testing our understanding of drugs that require a prescription from a registered medical practitioner due to their potential for misuse, abuse, or harmful side effects.

**Why the Correct Answer is Right:**

Correct Answer: Bromocriptine

Bromocriptine is a dopamine agonist used for the treatment of hyperprolactinemia, Parkinson's disease, and diabetes mellitus. It is prescribed by registered medical practitioners due to its potential for misuse as a recreational drug, leading to addiction or other adverse effects.

**Why Each Wrong Option is Incorrect:**

A. Pethidine (Demerol) - This drug is a synthetic opioid analgesic used for moderate to severe pain relief. It is not typically associated with a prescription-only warning for its misuse or adverse effects.

C. Quinine - Quinine is an antimalarial drug and is generally safe when prescribed by a medical practitioner. The warning could be due to potential side effects or contraindications, but not misuse or abuse.

D. Phenobarbitone - Phenobarbitone is an anticonvulsant and sedative-hypnotic medication. Although it has potential for misuse or abuse, the warning might be due to its risk of liver damage or other severe side effects, rather than misuse or abuse.

**Why Each Wrong Option is Incorrect:**

A. Pethidine (Demerol) - This drug is a synthetic opioid analgesic used for moderate to severe pain relief. It is not typically associated with a prescription-only warning for its misuse or adverse effects.

C. Quinine - Quinine is an antimalarial drug and is generally safe when prescribed by a medical practitioner. The warning could be due to potential side effects or contraindications, but not misuse or abuse.

D. Phenobarbitone - Phenobarbitone is an anticonvulsant and sedative-hypnotic medication. Although it has potential for misuse or abuse, the warning might be due to its risk of liver damage or other severe side effects, rather than misuse or abuse.

**Clinical Pearl:**

Bromocriptine (Bromocriptine, marketed as Parlodel) is a dopamine agonist used as a medication to treat Parkinson's disease, hyperprolactinemia, and acromegaly. Its prescription-only warning is likely due to the potential for misuse or abuse, which could lead to addiction, respiratory depression, and cardiovascular complications. This highlights the need for proper prescribing practices and patient monitoring to prevent misuse and its associated risks.