Why do drugs so drastically affect one person versus another? One person can take a sip of alcohol once and be an alcoholic for life. One person can take OTC narcotics and have almost no effect, while another person takes the same drug and knocked out for hours. Why are there such vast differences when for the most part, our biology is so similar?
In: Chemistry
Drugs interact with you via your neurons. The link between them (synapsis) can be filled with different substances. These substances encourage or inhibit the signaling in your body. The mechanism behind this is similar to a lock. Some substances act as keys for receptors, which in this analogy would be the locks. The amount of receptors you have is determined by your genetics and by a learning effect. Everyone has different genetics (except identical twins) therefore the reaction to drugs differs from person to person.
A whole lot of biochemistry goes into this answer and I’m probably not the most qualified to ELI5 it all and the answer is complicated.
Things like patient size(height/wt), dose, ethnicity can all play a role. For example we know people of Asian heritage produce less of the enzyme that breaks down alcohol(alcohol dehydrogenase) and therefore get drunk easier.
We also know that “ginger” people process anesthesia differently.
The reasons aren’t quite fully understood. But it comes down to biochemistry, dose, patient size. There is a TON going on.
Many drug interactions are actually due to a change in a third player. Drugs are broken down in the body. Whatever chemical is responsible for breaking it down can also be affected by the drug or by another drug. Let’s say drug A is broken down by chemical B, but you are also taking drug C, which has a side effect of making chemical B work a lot faster. Since chemical B is working faster, drug A is broken down very quickly, so drug A isn’t working very well in your body.
You can also have where drug C could make chemical B work very slowly, so the amount of drug A in your body can get to be very high (since your body isn’t getting rid of the drug fast enough) and you can then experience a lot of drug A’s side effects.
Sometimes a drug can be broken down into a toxic chemical, but normally it’s broken down at a rate where it’s still safe. Having an interaction where the drug is broken down into the toxic chemical very quickly can be poisonous.
Bonus: some drugs that you take are not active until they are broken down in the body, so you can have the opposite relationship where a lot of breaking down actually gives a lot of drug A side effects and slow breakdown makes it so the drug doesn’t work.
Each person has one of several different kinds of serotonin in their brain that react with drugs differently.
That and a bunch of other stuff.
In terms of addiction, the answer likely has less to do with biological differences and more to do with social factors.
I wrote my thesis on the mechanisms of cocaine dependency in rodents. One of the most interesting studies I read involved placing rats in “standard” and “enhanced” living conditions and givng them access to cocaine. The standard condition was a single rat housed in a cage with nothing except a water bottle, a tray of food, and a lever which would give them a small dose of cocaine. Rats are normally social animals, so the isolation is considered a significant stressor. The enhanced condition was a large cage with multiple rats, toys which were swapped out regularly, and simple puzzles which they had to complete to get food. The rats in the enhanced condition had the same access to cocaine, but took far less overall and had lower scores on “addiction-like behavior” tests.
While it wouldn’t be correct to say humans have the exact same behavioral patterns, there are definitely similarities. A person who has a strong social network, low stress, and an engaging lifestyle is likely not going to be as susceptible to addiction as someone under high stress who has little support. Essentially, if you’re bored, stressed, and lonely, you’re a lot more likely to take drugs.
Now genetic factors do absolutely play a role. In my experiments, all my rats were housed in identical conditions and were bred to have as little genetic diversity as possible (while maintaining a healthy population). I still had individuals who took far more drug than the average and some that hardly took any at all. There has likely been research into why this is, but I have not read it.
Different Genetics
Different Environment
Down to the rawest ELI5, this is the absolute answer.
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