Why are there no “perfect drugs” that work well without side effects?


It seems like the more potent a drug/medication is, the more risks are involved with it, where as drugs with very little risk don’t help nearly as much.

In: Biology

You’ve mostly answered your own question: the downside to drugs that do a lot is that they do a lot, and the downside to drugs that don’t do much is that they don’t do much.

There are some drugs that are great and have almost no risk, but the fact that they exist means that other drugs for the same treatment don’t get used anymore.

So the only time you see multiple drugs for the same issue is when there’s a tradeoff involved.

If you want the drug to make a “change”, then you run the risk of side effects, and you are right that the magnitude of the side effects can be related to the size of the change.

Organisms are highly optimized, if it takes work to make a molecule then using the same molecule for many tasks is more efficient than making a different molecule for every task. When a drug changes the rate or production for the molecule, all the tasks that use it are impacted. Maybe you want to drug to change one task so you feel better, but the molecules are all impacted and there will be side effects.

Much of drug research is trying to make very exotic changes so that the net effect is more like what you want. Unfortunately, every person is different, and a different balance of tasks leads to a different amount of side effect.

I think the answer is there’s not really such a thing as “side effects.” There’s just “effects.” A decongestant “may cause drowsiness” as a side effect and the very same drug as a sleep aid “may cause dry mouth” as a side effect. The drug is the same, it’s just whether the effects of the drug are advertised on the front of the box or not.

The body has a limited set of tools to interact with. Some tissues and organs use the same tool in different ways. While one organ may take a screwdriver to tighten screws, another may use it to pry things, while one more may use it to poke holes.

When a doctor diagnoses someone with a few screws loose, the doctor could have the patient take a medicine that gives more screwdrivers. Sure that helps the one organ manage to tighten screws but the other organs, now with more screwdrivers, will start to pry more things and poke more holes. These unintended effects are side effects.

A real life example is the body’s response to opoids. Opoids are used as powerful painkillers because they imitate other chemicals in the body that block receptors that transfer the pain response to the brain. The same chemicals also trigger your gut to push your digested food down and out! One side effect of opoids is constipation. The drug brand Imodium, an anti diarrhea medicine, is actually an oral opoid that helps stop your gut from pushing too much. It’s dose is not high enough to cause the pain relief for the brain but people have tried abusing it this way.


On the molecular level drugs are generally telling your body to do something different. That signal change usually tells a bunch of other processes to behave differently, which in turn tell a bunch of other processes to behave differently, and so on. You can have a drug that only changes “one” thing and a zillion functions behave differently.

It depends on what you consider a side effect. For a young, healthy person, there are many drugs which won’t cause any negative effects at all. For instance, most people who take acetaminophen (paracetamol) at appropriate doses for a headache will not experience any negative effects. Same goes for calcium carbonate tabs for heartburn, non-sedating antihistamines for allergies, etc.


There are about a bazillion listed side effects for almost any drug, but this is from large studies – if you take thousands of people with different genetics, ages, and health conditions, someone is bound to get negative effects from almost any medication. Likewise, taking any substance at much higher than the recommended dose (e.g. overdosing) will almost always result in negative effects – this is even true of something like water or food!


That said, if something is said to have absolutely no effects other than the intended one, there’s a good chance that it’s utter BS and doesn’t even do that (e.g. homeopathy).

They cause an imbalance in the four humors of the body, if you minimize one humor another is certain to rise!

From Douglas Adams:

“The term `holistic’ refers to my conviction that what we are concerned with here is the fundamental interconnectedness of all things. I do not concern myself with such petty things as fingerprint powder, telltale pieces of pocket fluff and inane footprints. I see the solution to each problem as being detectable in the pattern and web of the whole. The connections between causes and effects are often much more subtle and complex than we with our rough and ready understanding of the physical world might naturally suppose, Mrs Rawlinson.

“Let me give you an example. If you go to an acupuncturist with toothache he sticks a needle instead into your thigh. Do you know why he does that, Mrs Rawlinson?

No, neither do I, Mrs Rawlinson, but we intend to find out. A pleasure talking to you, Mrs Rawlinson. Goodbye.”

In other words, your body is an interconnected whole, not a bunch of independent systems. You can’t tweak something in one place without affecting other parts of the system.

What starts with a C and ends with an annabis?

Overly simplified –>

Its like a mathematical equation – you can’t just do one thing to one side of it. We’re all running in equilibrium, even if its not an ideal equilibrium, and when you take something you are knocking YOUR body out of equilibrium, so it will react in some way.

I’d say caffeine is pretty close to a perfect drug (when used in moderation). The primary routes of adminstration, coffee and tea, both show life extending properties. The only problems come from overdose or withdrawal, and even a perfect drug would have withdrawal.

There is a saying, ‘There is nothing strong enough to help you, that isn’t also strong enough to hurt you.’ A big part of medicine is making sure that the trade offs are understood and that the downside is outweighed by the positive effect. Since a core concept in medicine is ‘informed consent’ you have to be made aware of these… but people are bad at understanding the trade offs.

The body runs on a bunch of balances. Water is a good example, as you know, not enough and you die… but conversely if there is too much water to everything ratio, you also die.

Medicines change something that affects that balance. But often that then affects the balance of something else, something unintended. That is the side effect. In many cases the medicine might have another use where that side effect is actually the primary effect (say sleepiness with allergy meds) and the primary effect in the other case is now a side effect.

Many systems in the body are regulated with various neurotransmitters, proteins, ions, and the like. They work like glorified keys in locks, where some are master keys that work in many locks, others with very unique keys that only work in one place.

The goal of any pharmaceutical therapy is to find a drug that acts on only the locks that are problematic, while affecting the fewest other systems. Unfortunately as before, there is a tonne of interplay between the systems.

Aspirin (ASA) thins the blood (because [reasons](https://en.wikipedia.org/wiki/Aspirin)). Have a headache or a heart attack? Take Aspirin, ASA thins the blood, allowing it to flow into constricted areas to reduce the pain or help deliver more oxygen. Have a bleeding stroke or bleeding disorder? Take aspirin and the thinner blood will…bleed even more easily. It’s not so much that aspirin is a ‘cure headache key’, it’s a ‘thin the blood’ key (among other effects).

To the original question – why isn’t there a perfect drug for a specific ailment? Because many body systems have overlap between their systems. The same thing regulating your blood pH balance can be responsible for digestive acid production and some other liver function. Affecting any one stage will carry on further down the line. Frankly, the fact that our bodies work at all is nothing short of astounding. Tens of thousands of chemical processes in delicate balance with slight perturbations causing disease and death.

Caffeine is actually a remarkable drug. It creates alertness without any serious side effects.

If it wasn’t so common we’d be amazed by it.

The body is a very complicated machine. It is constantly self-adjusting. Drugs are like taking a 9lb hammer and banging on something — it’ll fix that one thing but it throws off other connected things (and things are not always connected in immediately logical ways). The drugs tend not to absorb at a steady rate (taking a pill for example) vs the gradual ebb and flow of bodily functions, so also throws off the machine.

On top of all of your body’s biochemical overlap, which has been addressed in other comments, there’s a selective effect in which drugs get approved for use.

A more potent drug for a more serious condition might be worth enduring the side effects. You’d risk nausea and hair loss to save your life from cancer, but probably not to alleviate a headache.

Your brain has hundreds of levers (neurotransmitters) that it uses to tell you what’s going on. When good things happen, it sends moves some levers and you feel good. Drugs work by going in and messing with all the levers, so you feel/think/see things that aren’t appropriate for what is going on around you. This can sometimes damage the levers (or the parts that listen to the status of the lever) because your brain is only supposed to have certain levers on for a certain amount of time.

Damaging those levers (by keeping them on/off too long) can cause long term damage resulting in a world of disorders often including depression and long term paranoia.

We don’t know enough about the human body so we are targeting broadly across many areas.

If we target depression we might target serotonin but serotonin modulates a lot of other functions and we don’t know how to target serotonin in just the brain, most serotonin receptors are in the stomach so a common side effect is nausea.
Now we know after 30+ years of targeting serotonin that serotonin might be just modulating something else and that something is what we should be really targeting.