Like when some one is addicted to drugs, does it have a chemical mechanism, or is it because that person mind got use to that??
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The short answer is yes. Most literature on the subject now differentiates between physical and psychological addiction. Both in a way involve chemical signaling.
With a physical addiction, chronic use of the substance in question causes physical withdrawal signs in the absence of the drug. The body tries to keep certain parameters roughly stable (e.g. blood pressure, brain activity, hormone levels) and many drugs depress or elevate these processes. Thus if you suddenly stop, the body has already adjusted to having the drug. The severity of these effects varies with the drug used.
For example in a heavy drinker, alcohol chemically depresses the brain and body, the body adapts by producing more of some stimulatory chemicals, such as epinephrine/adrenaline & NMDA (increases brain activity), and less of some depressive chemicals, such as GABA (decreases brain and muscle activity). Thus if this person stops drinking suddenly the body has way too much stimulatory chemicals and way too few inhibitory ones. This explains why this person would become anxious, confused, and jumpy. This person could have a raised heart rate and blood pressure, difficulty sleeping, and develop a fever. These rebound effects could cause the person to experience hallucinations, seizures, or even die (from seizures or heart failure).
Besides alcohol, some drugs that cause physical dependence are: barbiturates, benzodiazepines (e.g. valium), nicotine, quaaludes, and steroids.
However, many drugs have a psychological addiction mechanism which is also chemically based. It's important to realize that these may not cause measurable physical signs of withdrawal (i.e. a doctor wouldn't be able to measure a difference in your vital signs) or cause death from quitting, but the effect on the individual is still profound. Many drugs act by hijacking the "reward center" of the brain. Normally the brain releases dopamine when you are doing something enjoyable or fun and to help cope with physical pain. Similar to physical addiction, the addicted brain will adjust to this and release less and less dopamine in response to normal "fun" stimuli and require more of the drug to release dopamine. Thus an addicted person would have to take more and more to achieve the same level of dopamine release. When withdrawing the person could experience varying (depending on drug and level of addiction) depression and body pain. Drugs that operate via this mechanism include cocaine & marijuana (to an extent).
Some drugs operate both ways like opioids (e.g. heroine and pain killers) & methamphetamine.
Some drugs don't really have a clear cut addictive chemical mechanism (that we know of) and may simply be based on the user liking the way they feel on the drug. Many of these are hallucinogens like LSD. Marijuana also is proposed by many to be in this category as it's effect on dopamine is mild.
So I guess this turned into a long answer, but essentially yes there is a direct chemical mechanism explaining addiction for most of the drugs we think of as addictive.
With a physical addiction, chronic use of the substance in question causes physical withdrawal signs in the absence of the drug. The body tries to keep certain parameters roughly stable (e.g. blood pressure, brain activity, hormone levels) and many drugs depress or elevate these processes. Thus if you suddenly stop, the body has already adjusted to having the drug. The severity of these effects varies with the drug used.
For example in a heavy drinker, alcohol chemically depresses the brain and body, the body adapts by producing more of some stimulatory chemicals, such as epinephrine/adrenaline & NMDA (increases brain activity), and less of some depressive chemicals, such as GABA (decreases brain and muscle activity). Thus if this person stops drinking suddenly the body has way too much stimulatory chemicals and way too few inhibitory ones. This explains why this person would become anxious, confused, and jumpy. This person could have a raised heart rate and blood pressure, difficulty sleeping, and develop a fever. These rebound effects could cause the person to experience hallucinations, seizures, or even die (from seizures or heart failure).
Besides alcohol, some drugs that cause physical dependence are: barbiturates, benzodiazepines (e.g. valium), nicotine, quaaludes, and steroids.
However, many drugs have a psychological addiction mechanism which is also chemically based. It's important to realize that these may not cause measurable physical signs of withdrawal (i.e. a doctor wouldn't be able to measure a difference in your vital signs) or cause death from quitting, but the effect on the individual is still profound. Many drugs act by hijacking the "reward center" of the brain. Normally the brain releases dopamine when you are doing something enjoyable or fun and to help cope with physical pain. Similar to physical addiction, the addicted brain will adjust to this and release less and less dopamine in response to normal "fun" stimuli and require more of the drug to release dopamine. Thus an addicted person would have to take more and more to achieve the same level of dopamine release. When withdrawing the person could experience varying (depending on drug and level of addiction) depression and body pain. Drugs that operate via this mechanism include cocaine & marijuana (to an extent).
Some drugs operate both ways like opioids (e.g. heroine and pain killers) & methamphetamine.
Some drugs don't really have a clear cut addictive chemical mechanism (that we know of) and may simply be based on the user liking the way they feel on the drug. Many of these are hallucinogens like LSD. Marijuana also is proposed by many to be in this category as it's effect on dopamine is mild.
So I guess this turned into a long answer, but essentially yes there is a direct chemical mechanism explaining addiction for most of the drugs we think of as addictive.