Why Do People Respond Differently to Drugs?

Content medically reviewed by Vicky Magobet, PMHNP-BC, on October 12, 2019.

The effects of drugs vary from person to person. Two people can take the same amount of a substance and feel different results. Do you ever wonder why people have unique responses to drugs or why some people have a higher chance of getting addicted than others? Multiple factors come into play.

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7 Reasons People Respond Differently to Drugs

1. Tolerance

Someone who takes a drug on a regular basis can build a tolerance. When this happens, they feel fewer effects from the drug over time. The body adapts to its presence and needs a higher amount for the person to feel the same results. Taking certain drugs can cause you to develop a tolerance at a faster rate than others. For example, the way opioids interact with the body creates a tolerance in a short time.

2. Body Mass

A person's size and amount of fat and muscle impact their reaction to a drug. Larger people also have larger vascular systems, meaning that a substance must travel in more blood. The higher volume of blood dilutes the drug, so its effects aren't as strong.

There are also fat-soluble drugs stay that in the system for a long time when the person has a high amount of fat tissue, with effects that are less pronounced. Meanwhile, non-fat-soluble substances focus on muscle mass and have a stronger impact on those with less muscle.

3. Age

As someone gets older, they need less of a drug to feel its effects. They develop more fat tissue in relation to muscle, so a drug lasts for a long time. The liver reduces in size and effectiveness over the years as well, so its capacity to absorb and filter various drugs decreases. An older person's receptors also become more sensitive as they age.

4. Sex

Most people have hormones and body sizes dependent on their biological sex. Men tend to have bigger body sizes and lower fat tissue proportions than women, so various drugs affect them in different ways.

For women, even different phases of the menstrual cycle can change someone's sensitivity to certain drugs. For example, certain phases can cause a stronger reaction to stimulant drugs than others.

5. Genetics

Someone's genetic makeup influences the way they absorb drugs. Genes determine the activity of the enzymes that help the body metabolize drugs. Most gene differences create small changes, but some types of genetic coding prevent the enzymes from working. In some cases, genes cause someone to process drugs at a rapid rate, creating an unpleasant response. 

Four main types of metabolizing genes show the different ways drugs can be metabolized:

  1. Poor metabolizer: When medication is broken down very slowly, it stays in the body's systems longer than needed. A person may experience side effects even with a standard dose.
  2. Intermediate metabolizer: Breakdown of the medication is slower than normal but not poor in function. The person may be subject to potential side effects.
  3. Extensive metabolizer: This is the standard rate of metabolism. It can also be described as the normal amount of medication at the usual doses.
  4. Ultrarapid metabolizer: The medication is broken down too quickly and is removed from the individual's system before it has a chance to provide relief.

6. Environment

The environment in which someone grew up can significantly affect the likelihood of drug addiction. Addiction is typically linked to a learned behavior in a certain environment where the person acquires knowledge of the substance and how to use it. Addiction all boils down to the physical, emotional and social aspects of a home, school, work environment and more.

A stressful and abusive early home environment for a child can drive them toward substances for a source of comfort — especially if their home includes exposure to these substances. If someone learns that using drugs and alcohol is a normal behavior or acceptable coping mechanism, they will also choose a similar behavior in their life. This concept also is true for learned behaviors from those they surround themself with, like friends and acquaintances and what those individuals deem acceptable.

7. Existing Health Conditions

Existing health conditions can create a higher risk of addiction, even though it is not always the health condition itself — it is usually the treatment. In 1995, OxyContin was introduced as a less-addictive opioid pill to treat chronic pain — though this was not the truth. Over the next two decades, doctors prescribed this medication, not knowing its addictive properties. The opioid crisis has provided awareness of how even prescription drugs must be taken cautiously. 

The possibility of addiction also goes for mental health conditions like depression, anxiety, PTSD and more. Some antidepressants contain ingredients that can lead to addiction if they are misused. Dependence on a specific drug can connect to a person's environment — the more available this drug is, the more likely it is to be used and misused. Having a health condition can act as the gateway to receiving addictive substances.

Factors Behind Substance Abuse

Some people have a higher chance of developing an addiction or substance abuse than others due to biological and social factors. Since the way we react to drugs has genetic causes, people with family histories of addiction have a risk of also getting addicted. Trauma and mental health issues also contribute to someone's likelihood of substance abuse. In certain cases, the person dealing with substance abuse started using a drug to self-medicate without realizing it.

At Diamond House Detox, we specialize in finding these underlying factors and addressing them so you can heal. Our dual diagnosis approach allows us to treat the causes and results of your substance abuse. If you need a partner in your journey to recovery, let us help. We welcome you to contact our team today. Call today for same-day admittance at (888) 205-9455.