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Pharmacodynamics is a branch of pharmacology. While pharmacokinetics can be described as what the body does to a drug, pharmacodynamics is what the drug does to the body. It studies the relationship between drug concentration and effect.

Pharmacodynamics: What does it have to with illicit drug use?

Pharmacodynamics of illicit drugs is studied most often in relation to the production of euphoria and the development of tolerance to certain drugs. All drugs of abuse cause euphoria and most produce tolerance. Addicts know that over time, they need more and more drugs to produce the same high. This is known as tolerance.

When you take a drug, it binds to certain receptors in the brain. The extent of binding and the number of receptors is the main focus of pharmacodynamics. Some drugs bind to receptors and stimulate them. These are known as antagonists. Most illicit drugs have this effect. Some drugs bind to receptors and partially stimulate them, but also block other drugs from binding. This is the case for drugs like Suboxone. It binds to opiate receptors and stimulates them partially, which helps to treat opiate withdrawal symptoms. It also blocks other opiates from binding, so if you shoot heroin after taking Suboxone, you won’t get high. This 2-fold effect is why Suboxone is used to treat opiate dependency. Some drugs bind and do not stimulate the receptor at all. They just block other drugs from binding. Naloxone is an opiate antagonist. It will prevent you from getting high from other opiates, but it does nothing to treat opiate withdrawal. This is why naloxone is used as more of a long-term preventative drug instead of a detox drug.

When a drug is taken over a long period of time, the body responds to the presence of the drug by increasing or decreasing the number of receptors for the drug depending on the drugs effect on the receptor. For antagonists, the body responds by decreasing the number of receptors and the “responsiveness” of each receptor. So not only does the body have fewer receptors, the receptors themselves are less responsive. Also, the body produces less of whatever natural chemical normally binds to the receptor.  This is tolerance, and for drugs with a high addictive potential, it occurs in a relatively short period of time. When the body becomes tolerant of a drug and drug use is stopped or significantly reduced, the body experiences withdrawal.

This is why, for example, opiate withdrawal is so painful. The body produces natural “opiates” or pain-killing chemicals. Over time, when the body is getting a steady supply of outside opiates (like heroin or roxies) it produces less natural opiates. Also, there are fewer opiate receptors and the receptors are less responsive. This is the essence of pharmacodynamics-the body’s response to drugs. It does this to try to maintain equilibrium. When the opiates are taken away or reduced, the body reacts in an extreme way.

Pharmacodynamics is important in studying the effect of drugs on the body and in the development of new drugs.

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*This is an informational based article and is not intended to replace the advice or knowledge of a medical professional.*

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