Final answer:
Carl was likely taking heroin, an opioid that reduces brain production of endorphins, leading to severe withdrawal symptoms upon cessation. Methadone is used in treating heroin addiction due to its ability to reduce cravings and withdrawal symptoms without high abuse potential. Withdrawal symptoms from physical dependence include pain, seizures, and psychological effects like anxiety and depression.
Step-by-step explanation:
After taking a psychoactive drug for many years and experiencing physical pain upon withdrawal resulting from the cessation of the drug's induction of brain production of endorphins, the drug Carl was taking is likely heroin. Heroin is a well-known opioid that causes the brain to reduce its own production of endorphins, which are natural painkillers and mood elevators, leading to severe withdrawal symptoms that include pain when the drug is discontinued.
A person with a heroin addiction may be prescribed the psychoactive drug methadone as part of a treatment program because methadone acts on the same opioid receptors as heroin but causes less euphoria and is longer-lasting, thereby reducing cravings and withdrawal symptoms without the same high risk for abuse and overdose.
Possible withdrawal symptoms associated with physical dependence
Common withdrawal symptoms from physical dependence on psychoactive drugs like heroin may include tremors, pain, seizures, insomnia, anxiety, depression, and paranoia. These physical and psychological withdrawal symptoms are signs of the body re-adjusting to the absence of the drug.