Why do people suffer extreme withdrawal effects when they stop taking some drugs but mild to no withdrawal when they stop taking other drugs?

http://www.addictionsandrecovery.org/withdrawal.htm

http://en.wikipedia.org/wiki/Withdrawal

The severity of withdrawal effects when discontinuing drug use can vary depending on several factors, including the specific drug involved, the duration of use, the dosage, and an individual's biology and sensitivity to the drug.

Drugs that typically lead to extreme withdrawal effects, such as opioids (e.g., heroin, oxycodone) and benzodiazepines (e.g., Xanax, Valium), often affect the central nervous system and may cause physical dependence. When these drugs are used consistently and in high doses, the body adapts to their presence and relies on them to function normally. When the drug is suddenly removed, the body goes through a period of adjustment, resulting in withdrawal symptoms. These symptoms can be intense and unpleasant, including nausea, restlessness, anxiety, muscle pain, insomnia, and in severe cases, seizures or hallucinations.

On the other hand, drugs that are less likely to cause severe withdrawal effects, such as certain antidepressants or stimulants like Adderall, typically do not produce the same level of physical dependence. While there can still be some withdrawal symptoms, they are generally milder and more manageable.

It's important to note that the severity of withdrawal symptoms can also be influenced by how the drug use is discontinued. Abruptly stopping certain drugs can result in more severe withdrawal, whereas gradually tapering off or using medication-assisted treatments under medical supervision can help mitigate the intensity of withdrawal symptoms.

Ultimately, the specific mechanisms of each drug, as well as individual variations, play a significant role in determining the severity of withdrawal effects.