How Do Medicines Work In The Body?


What happens to medications once they are in our bodies? Where do they go? How do they get there? What functions do they carry out?

Millions of pills, syrups and potions are ingested in some form or another by humans on a daily basis. It may then be beneficial to us all to know exactly what happens inside our bodies when we have taken some form of medication.

Medicines not only have many functions but there are a number of routes they can enter the body.
Medicines not only have many functions but there are a number of routes they can enter the body. | Source
Swallowing medication is the most common way for them to get into the body.
Swallowing medication is the most common way for them to get into the body. | Source

What medicines do for us

Medicines work in a variety of ways depending on what they are taken for and in what form.

Some examples of why we take medication are:

  • pain relief
  • to fight infection
  • to fight disease
  • to supplement a deficiency
  • to assist a body mechanism to correct itself
  • to decrease an overabundance of a body substance
  • to balance systems and organs in the body

But in addition to what we take, there is also the route and form by which a medication is taken:

  • Oral - tablet, capsule, syrup, drops etc.
  • Sub-lingual, (under the tongue) - tablet, drops.
  • Skin preparation - cream, ointments, gel, patches and so on.
  • Injection - by hypodermic needle.
  • IV - Intravenous - needle into a vein.
  • Into the bowel - suppository/enema.
  • Inhalation - steam inhalation, crystals, and inhaler.
  • Drops - ear/eye/nose.

How medicines are processed by the body is an intricate process, but we can simplify this by breaking the steps down into four main areas:

  • Administration - we take in the medicine by the form and route as mentioned earlier.
  • Delivery - once the medicines are inside our body they move into the blood stream then into organs and tissues.
  • Performance - medicines will produce or induce effects.
  • Elimination - the body will wash out medicines and waste products associated with them.

Therefore the type and route will have an effect on where the drug will enter the body and what areas the drug may target. For example, inhalations are primarily to assist with breathing.

The route and type of medication also has an effect on how quickly a drug will act. Intra-venous (IV) is a rapid method of medication administration, since the chemicals enter directly into the blood stream.

Injection into muscles – which are full of blood vessels - is also a very fast method of medicines getting into the body.

Suppositories and enemas inserted into the bowel through the anal opening can also be swift acting. This is due to the large surface area of the bowel that is packed with blood vessels, so absorbing the drugs very quickly.

These last 3 routes also by-pass the stomach where some or the entire drug could be destroyed or diluted by the hydrochloric acid.

Medicines are made in different ways in order that they will dissolve in the area of the body that will make them most effective.
Medicines are made in different ways in order that they will dissolve in the area of the body that will make them most effective. | Source

The most common route for medications

The most common route for taking medication is by mouth – also known as the ‘oral’ route. From here the medication has a journey to make that starts from our mouths to the target area inside the body.

Medicines in the digestive system

When medicines reach the stomach, some will start to dissolve. A few medicines will be absorbed into the stomach lining, whereas others will move onto the small intestine. It depends on the type of coating a tablet has whether it dissolves in the stomach or elsewhere.

Many drugs have special coats that protect the medicine inside from being destroyed by the stomach acid. Tablets in capsule form also often have this kind of protection. This is why it’s important not to open capsules or coated tablets and swallow the medicine inside.

In addition, some medicines inside coated ones might be harmful to the lining of the stomach. This happens because some medications induce the stomach to produce higher levels of hydrochloric acid in the stomach that can be harmful.

Medications that haven’t been processed fully by the stomach move into the small intestine.

Medications are absorbed into the lining of the small intestine which is made up of three parts:

  • The duodenum
  • The Jejunum
  • The Ileum

From the small intestine medications will move into the blood stream.

Medicines in the circulatory system

No matter what form a medicine takes they will be dissolved and enter the blood stream at some point.

Medicines are circulated around the body and delivered to organs and tissues. This process is very fast. The heart can pump a full cycle of blood in about one minute. During this process the medicine molecules are being delivered throughout the body. The brain will receive the largest portion - about 16%.

The effects of the medicine will continue to be active until metabolism begins. (Metabolism is the biochemical activity of a substance within a living organism.)

The metabolism for each medicine is different. In other words some are broken down and prepared for elimination more quickly than others.

That is why some medicines will be given frequently, for example 2-4 hourly, others less so. In fact some medicines may already be breaking down when they passed through the liver for the first time - this is called 'first-pass effect’.

Some categories of tablets and capsules may have to go through the liver several times before they can be eliminated from the body.

Medicines within the body tissues and cells

Within the body tissues we eventually get down to the cellular level.

The cells of the body can absorb fluids and so will soak up the molecules of medicine from the blood that surrounds them.

Not all medicines will start to work at the same time. This is because different medicines all have their own specific molecules that will dissolve either quite quickly or more slowly than others.

In addition some medicines find it easier to dissolve in human tissue than others.

Human cell membranes have a high content of fats. Therefore, if you have a medicine that can dissolve in fat then they will begin to work more quickly than those that can't.

This ability to dissolve in fat is a very important point when thinking about how fast a drug will begin to act.

Once the dissolved medications are within the cell this is where most of them do their work through biochemical reactions. They then re-enter the blood stream where they will once again enter the liver. Here they will be broken down further and prepared to be eliminated by the body.

Eliminating medicines from the body

The main organs associated with elimination of medicines are the liver and kidneys.

Basically these organs sieve out toxic substances. The liver breaks them down through a series of complex metabolic reactions. These toxins/waste products are then stored by the liver until it is ready to send them to the kidneys.

In the kidneys the prepared substances are further processed and then eliminated from the body through the urine.

Medications make a long journey around the body before finally being prepared by the liver and elimanated by the kidneys.
Medications make a long journey around the body before finally being prepared by the liver and elimanated by the kidneys. | Source

Medications and the Brain

As mentioned earlier, medicines enter the blood stream once they have been dissolved and travel throughout the body to various organs including the brain.

Once in the brain some medications can affect chemicals called neurotransmitters.

The neurotransmitters are special elements responsible for controlling the signals sent between brain cells. These brain cells are called neurones.

Specialised neurotransmitters are also responsible for affecting people's feelings and moods.

However, it’s not always possible for medicines to get access to the brain. This is because the brain has a safety device called the 'blood-brain barrier' – ‘BBB’ for short.

This in effect helps to prevent things such as bacteria, toxins and unwanted molecules from entering the fluid that directly surrounds the brain.

However, what this does mean is, if infection infiltrates the defences then medications such as anti-biotics, whose molecules are large, cannot cross the BBB to fight the bacteria.

Having said this, with infection, inflammation develops and this is one symptom that will weaken the barrier and may allow anti-biotics to filter through.

Other medications that are required to access the brain directly need to have specialised fat-soluble properties in order to get through the BBB's defences.

In some areas of the brain the BBB is deliberately weak. This allows the brain to monitor the composition of the blood and to take action if adjustments are needed.

There are conditions and diseases that can weaken the BBB to a dangerous level allowing other harmful substances to pass through. Some of these conditions are:

  • Hypertension
  • Very high exposure to microwaves and radiation
  • Infections
  • Head trauma
  • Ischaemia
  • Inflammation
  • Abnormal Pressure around the brain.
  • Meningitis
  • Epilepsy
  • Multiple Sclerosis
  • Alzheimer's disease
  • HIV Encephalitis
  • Viruses

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Taking Medications

Have you ever made a mistake while taking medications? For example too many or missed a dose?

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Factors that affect the medications you take.

There are quite a number of factors that will influence both the absorption rate and the metabolism of medicines:

  • Physical
  • Food
  • Other medications/chemicals

These factors will in turn decide how effective the medication is.

Physical Factors

These include:

Your weight,


Fat mass,

Muscle mass.

All these aspects either speed up medicine absorption or slow it down.

If you have a good amount of fat mass for example, then it will have an affect on how long it takes to target the specific area and how effective the medicine will be when it gets there.

In relation to age - younger people tend to be able to metabolise and eliminate medications quicker and more thoroughly than older people. Therefore doctors will often moderate the dosage of tablets for an elderly person.

Babies and young children have to have a moderated dosage as well since their bodies are still maturing. This means their organs could be more easily damaged by the toxic affects of medicines.

In addition, we are all genetically and chemically different. Some of us may tolerate a particular medicine more than others. This is why some people may suffer from either the *side effects or **adverse reaction of a medicine.

  • *Side effect - "An undesirable secondary effect of a drug" Encarta Dictionary
  • ** Adverse reaction - "...undesirable or harmful results from a medication..." Encarta Dictionary.

If you experience any problems with medicines you should consult your doctor or pharmacist immediately.


Food will slow down the absorption rate of medication. This can either be beneficial or detrimental to the medication's success rate.

That is why it is always important to follow the instructions given either by a doctor, pharmacist or on the leaflet that comes with the medication.

As an example, instructions may include:

  • To be taken before food
  • To be taken either with or after food
  • To be taken after food
  • To be taken with a full glass of water

These instructions are given so that the medications will work at their most effective. In addition, these instructions may also be to lessen the harmful effects that some tablets may have on the body.

Other Medications

These can also have numerous affects on medications. For example, if some medications are taken at the same time, they could cancel out the benefits of each other.

Some medications will increase or decrease the rate of absorption and metabolism in the body. So again, that is why it is important to follow the instructions given to you or that are stated on instruction leaflets.

For example you may see an instruction such as:

  • Not to be taken with alcohol
  • Do not operate machinery, or drive while taking this medication

I hope this article has been helpful to you in explaining how medications work in the body and the factors that can affect how they work.

If you are ever unsure about any medications that you have - whether prescribed or bought - then speak to a doctor or pharmacist as soon as you can.

© 2011 Helen Murphy Howell

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Comments 40 comments

melpor profile image

melpor 5 years ago from New Jersey, USA

Good hub and very informative. A lot goes on in body before medicines do their work.

Seeker7 profile image

Seeker7 5 years ago from Fife, Scotland Author

Hi melpor,

Many thanks for stopping by and for the nice comment. I think the more we learn about the human body the more amazing it is.

thiruselvamk profile image

thiruselvamk 5 years ago from MALAYSIA

Well written. There are many who do not complete the full course and of course this leads to increased dosage in future. Drug tolerance has resulted. The human body is amazing. How refined and specific each tablet is becoming as to work on the target organ with minimal side effects.

YES! the human body is amazing. Not at all discovered in its full. The mind is a mystery. The brains are a wonder. The nervous system is unique. The tissues are intricate.

The puzzle is that breath..... in and out and in and out.

Can anyone say when it will stop or why it stopped. The body is as amazing as the universe.

Seeker7 profile image

Seeker7 5 years ago from Fife, Scotland Author

Hi thiruselvamk,

Thank you for stopping by and for your comment. Yes!!! The human body is amazing. We go into space to explore other planets, yet we don't know everything about our own. We try to find alien life - yet we don't know everything about our own bodies. What an odd but fascinating species we are! Many thanks again for taking the time to write.

tysanders profile image

tysanders 5 years ago from Atlanta, Ga

This is very good information! I have always wondered how medicine works once inside the human body. Thanks for sharing.

Seeker7 profile image

Seeker7 5 years ago from Fife, Scotland Author

Hi tysanders,

Thanks for stopping by and for the great comment.

Sam9999 profile image

Sam9999 5 years ago

Very interesting and useful hub. Keep writing!!

Seeker7 profile image

Seeker7 5 years ago from Fife, Scotland Author

Hi Sam9999,

Many thanks for stopping by and the nice comment. Really appreciated.

Entourage_007 profile image

Entourage_007 5 years ago from Santa Barbara, CA

Great article Seeker7 - Its really interesting to think how prescription drugs and over the counter medications work. Especially the prescription pain killers, I've always taken an interest in understanding them because its good to know how these things work. Especially when your taking a medication that could potentially be addictive.

Seeker7 profile image

Seeker7 5 years ago from Fife, Scotland Author

Hi Entourage_007 - (love the name!). Many thanks for stopping by and for leaving such a nice comment. I think that you have made a very good point about understanding the medicines that we take, especially, as your rightly point out, when some of them can become addictive. I don't think people actually think about the effect that medicines might have on our body, especially if taking them over long periods of time. As a nurse, who specialises in elderly care, it is very common for an elderly person to be put on a drug, then when this drug causes a side effect, they need another one to counteract this and the vicious cycle goes on. They also occasionally end up in hospital due to the toxic effects from some drugs, for example the heart medication Digoxin. So in effect drugs can cause more harm than actually helping. Many thanks again for your interesting comment.

acaetnna profile image

acaetnna 5 years ago from Guildford

I am so very concerned about the use of medication, particularly with the elderly. Drugs can definitely cause more harm than good and I feel that we need to be totally aware of this. A great hub - thank you.

Seeker7 profile image

Seeker7 5 years ago from Fife, Scotland Author

Hi acaetnna,

Many thanks for stopping by and for leaving a good and insightful comment. I agree with you about drugs and in relation to elderly people. I remember working in the hospitals years ago and drugs would be given out to the patients, and then, although they had been prescribed for years, would suddenly be taken off the market because they were found to be "unsafe". Very scary stuff as all drugs are supposedly tested before use. I know all folks won't agree, but I think incidents like this show just how useless, (not to mention the cruelty factor), testing drugs on animals are and how dangerous drugs can be - both short term and long term for humans and animals alike.

Many thanks again for stopping by.

Nspeel profile image

Nspeel 5 years ago from Myrtle Beach

Amazing article you went very in depth and I am very against medicine so it was a good read for me. Keep up the good work voted up and useful.

Seeker7 profile image

Seeker7 5 years ago from Fife, Scotland Author

Hi Nspeel,

Lovely to hear from you and glad that you enjoyed the hub.

I agree with your view about medicines. We are mostly told about the benefits but it is clear to see what these chemicals can do in the body that is not a benefit.

It may seem a strange thing to say coming from a nurse, but working with elderly people for so long I have often seen them being admitted to hospital because of some unknown illness. They are frequently taken off a whole list of obscure medications and within a short period of time they feel a hell of a lot better. Just goes to show that although they do have their place but it should be in moderation.

Nspeel profile image

Nspeel 5 years ago from Myrtle Beach

Oh yeah they find a medicine to give you for everything when in reality most things could be dealt with yourself herbally.

Rehana Stormme profile image

Rehana Stormme 5 years ago

Voted up and useful. This is something I was wondering about last week when I fell ill and had to take strong anti-biotics. Somehow I stumbled upon this article and it all makes sense. Thanks for this!

Seeker7 profile image

Seeker7 5 years ago from Fife, Scotland Author

Hi Rehana,

Many thanks for leaving a comment and the vote up. I hope you are feeling better and glad that the hub was of some use to you. Take care.

Ingenira profile image

Ingenira 4 years ago

Voted up and tweeted. I often read about how medicine affects our body especially the kidney. You provided very comprehensive information here.

Seeker7 profile image

Seeker7 4 years ago from Fife, Scotland Author

Lovely to hear from you again Ingenira and again glad that you found the information useful. Thanks also for the 'tweet'!

molometer profile image

molometer 4 years ago from Cambridgeshire, England

Very interesting, highly detailed and well researched hub on medicines and how they work.

I have just started taking Melatonin for a sleep disorder and it was good to know how these are delivered to the brain.

The diagrams were useful too.

Excellent hub voted up interesting and useful.

Seeker7 profile image

Seeker7 4 years ago from Fife, Scotland Author

Hi molometer, many thanks for stopping by and glad that you found the hub useful. Sorry to hear that you have a sleeping disorder - hopefully the Melatonin will help you with this. I think when folks have to take medication, even for just the short-term, it's good to have at least a little knowledge of where the chemicals are going and what they are actually doing.

bookmonger99 profile image

bookmonger99 4 years ago from Saint Helens, Oregon USA

Just a few years back I was patting myself on the back for being my age, "elderly" and not taking so many pills. Now I find myself in the situation that so many elderly do, taking hands full. ugh.. but thank you for this article, did vote it up and tweeted it. Blessed Be. xx

Seeker7 profile image

Seeker7 4 years ago from Fife, Scotland Author

Hello to you bookmonger99 and many thanks for stopping by. I know what you mean about the pills, my Dad is the same now. It's like our minds and memories are forever young but the body doesn't keep up! I know my Dad hates having to take medication and I can understand that. Unfortunately having a heart condition and Parkinson's Disease he doesn't have much choice. But he would certainly be in sympathy with your own feelings about having to take 'handfulls'!

Many thanks again for leaving such an interesting comment and for the 'tweet'! It really is appreciated.

articlesocean profile image

articlesocean 4 years ago from London, United Kingdom

Great hub! I found it really useful. As your a nurse, hope you don't mind me asking, but I have been taking a medicine to cure allergy (urticaria) for more than 2 years now. its called cetirizine 10mg, and the allergy has just gone worse. Voted Up and useful !

Seeker7 profile image

Seeker7 4 years ago from Fife, Scotland Author

Hi articlesocean - sorry for taking so long to respond to you. Two years is quite a long time for one drug for urticaria. So it can mean one of two things. Either the drugs effectiveness has worn off or the drug is not solving the issue that you have. Do you know what the allergy is that you are suffering from? Or is it a general allergy? Depending on what you are allergic to, it might be that you will need to have a change of medication or a combination of medicines to combat this distressing condition!

Hope this helps a bit and many thanks for visiting - really appreciated!

articlesocean profile image

articlesocean 4 years ago from London, United Kingdom

That's alright, well the doctor has told me that its urticaria and when i searched for this it said that its another term for Hives. well maybe this drug isn't useful but it cures the allergy in 30 min to 1 hour, then its back again the next day. i have also tried to see by checking if it comes back by eating certain foods or some type of cloths, so i realized that i'm allergic to silk. can u recommend a drug for me? yes, this has helped thanks so much.

Seeker7 profile image

Seeker7 4 years ago from Fife, Scotland Author

I don't know if you've tried an over-the-counter remedy such as piriton or piriteze - these are the UK names. I've used them in the past and they have worked very well. There are also lotions and creams - herbal - that you can buy without prescription. You could also perhaps go to a chemist and see if they can give you a cream or lotion with hydrocortisone in it.

MargaritaEden profile image

MargaritaEden 4 years ago from Oregon

High quality article, very informative, answered some of the questions i had.

Seeker7 profile image

Seeker7 4 years ago from Fife, Scotland Author

Hi MargaritaEden,

Glad that you found the hub useful. Many thanks for stopping by and taking the time to leave such a positive comment - thank you!

wwolfs 4 years ago

Nice hub and very informative. You did a great job explaining how medicine works throughout the body. This is good information to know, and how there are many situations and other factors for the outcome and results of medication for each individual. Thank you for sharing.

Voted up and useful!

Seeker7 profile image

Seeker7 4 years ago from Fife, Scotland Author

Hi wwolfs - (love your profile photo of the wolf!),

Many thanks for stopping by and glad that you found the hub useful. As you rightly point out, there are so many factors that contribute to medication other than just swallowing them, so it is a huge and important subject area.

toknowinfo profile image

toknowinfo 4 years ago

Hi Helen, This is a fascinating topic. You explained it very clearly and in detail that is easy to understand. Thank you for putting this well done article together. I learned a lot and am sharing it on twitter, so others will learn also. Voted up, interesting, and awesome.

Seeker7 profile image

Seeker7 4 years ago from Fife, Scotland Author

Hi to knowinfo, many thanks for stopping by. Glad that you enjoyed the hub and found it useful. Thank you as well for the share on Twitter - greatly appreciated.

Seeker7 profile image

Seeker7 3 years ago from Fife, Scotland Author

Thank you!!

TomJarred 3 years ago

What a great page! This helped me with my science assignment. Could you make a page for lizzard species?

Seeker7 profile image

Seeker7 3 years ago from Fife, Scotland Author

LOL!! Hi TomJarred - I don't know that much about lizards to be honest, but maybe once I get through the hubs I'm working on!!

Glad that you found a use for the hub with your science assigment - that always makes the hard work of writing very worthwhile! Thank you also for the nice comment, very much appreciated!

eliani brian 2 years ago

wow, this really awesome, please help me with this

A drug swallowed as a pill or capsule may not make it into the general circulation in sufficient amounts to be effective. Explain different mechanisms that may account for this observation. Why might a drug delivered by a skin patch or nasal spray be more effective than the same drug taken orally?

Seeker7 profile image

Seeker7 2 years ago from Fife, Scotland Author

Hi Eliani brian,

Please accept my apologies for the delay in replying to you - I haven't been around Hub Pages for a couple of months or so. I'm g;ad that you enjoyed the hub and to answer your question:

The areas you describe such as the skin and the nasal passages have huge amounts of blood vessels very near the surface area of the body. Both the skin and the area within the nose have the ability to absorb all kinds of chemicals. When these chemicals are taken in by the body through the skin or nose, then they go directly into the blood stream. This way, the drugs or chemicals by-pass the destructive acid in the stomach and the digestive enzymes in the bowel.

Mel Carriere profile image

Mel Carriere 12 months ago from San Diego California

Fantastic summary, and very helpful. Too often we just pop pills and assume they just work magically, somehow. Thank you for this breakdown of the actual physiological process involved.

Seeker7 profile image

Seeker7 12 months ago from Fife, Scotland Author

Many thanks for stopping by and glad you enjoyed the hub.

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