How Medications Work in Your Body: Why the Way You Take Them Matters

Author: Emmanuella O'Ambrose, Bachelor of Pharmacy (BPharm), Reviewed by Dr Azuka Chinweokwu Ezeike, MBBS, FWACS, FMCOG, MSc (PH)

Highlights.

• Medications work best when taken the right way, as prescribed.
• The route of administration affects how fast and how well drugs work.
• Common routes include oral, rectal, sublingual, injections, topical, vaginal, and inhalation.
• Some drugs must be injected or inhaled to avoid being destroyed in the stomach.
• Wrong routes can reduce effectiveness or cause serious harm.
• Always ask your healthcare provider if you're unsure how to take a medication

 Introduction

Have you ever wondered why you lick vitamin C tablets? Why does it sometimes come in dissolvable forms? Some tablets dissolve quickly in the mouth, while others that dissolve in water release their nutrients slowly. When we take our medications, we must consider how our bodies receive them. Medications function by interacting with specific parts of the body.  How they are given, known as the route of administration, determines their effectiveness. Routes of administration are the different ways drugs enter the body. [1] Each route comes with its pros and cons. The most common route is through the mouth; some others include veins, gums, skin, nostrils, and much more. Continue reading to learn about the various ways to give drugs and the pros and cons of each. 

Route of administration 

How a drug is made, how your body absorbs it, and how well it works determine its efficacy. An asthmatic patient went to see her doctor with a singular complaint: her asthma was getting worse. She had barely escaped death the last time she had an attack. After asking her a few questions, the doctor discovered she did not know how to use her inhaler correctly. She sprayed it directly before her face instead of inserting it into her mouth. 

There are many other cases like these. Cases of patients taking suppositories with water when they should have inserted them into a body cavity. These scenarios show that every drug has a particular route it must use to enter the body to be effective.

Common Routes of Administration

It is necessary to use drugs via the proper routes to prevent drug interactions either with food or with other medications. The drug's properties and convenience determine its use, so knowing the routes and how to use them is crucial.[2] 

Routes of administration are classified into  three: 

1. Enteral route of medication
2. Parenteral route of medication
3. Others

 They are accurately represented in the table below.

1. Enteral Route of Medication

A. Oral route (by mouth)

• What it involves: Medications like tablets, capsules, or liquids taken by mouth.
• Why it’s commonly used:
  • Simple and convenient.
  • Cost-effective.
    
    
  • Doesn’t require help to take.
    
    
• Drawbacks:
  • Takes longer to start working because it has to be digested.
  • The dose may be reduced as the medication travels through the digestive system before reaching where needed.
  • Not ideal in emergencies because it’s slower.
    
    
• Example drugs:
  • Pain relievers (e.g., Ibuprofen).
  • Antibiotics (e.g., Amoxicillin).

B. Rectal route

• What it involves: Medications, like suppositories, are placed into the rectum.

• Why it’s used:
  • This is for patients who can’t take medications by mouth (e.g., due to nausea, vomiting, or difficulty swallowing).
• How it works:
  • The medication dissolves in the rectum and is absorbed into the body quickly.
  • It helps to avoid stomach irritation and digestive issues.
• Common uses:
  • Treating constipation, pain, or fever when oral medications aren’t an option.
• Example drug: Diazepam (used as a suppository to treat seizures when oral medication isn’t possible).
• Benefit: Works faster and more effectively for certain conditions than oral medications.
  
  

C. Sublingual route

• What it involves: It involves placing medication under the tongue, where it dissolves.

• How it works:
  • Absorbed directly into the bloodstream through tiny blood vessels under the tongue.
    
    
• Why it’s used:
  • It works quickly because of direct absorption into the bloodstream.
  • Ideal for emergencies or when rapid action is needed.
    
    
• Common uses:
  • Treating conditions that require fast relief (e.g., chest pain).
    
    
• Example drug: Nitroglycerin (used for chest pain or angina).
• Benefits:
  • Fast acting.
  • Easy to use, especially for those who have trouble swallowing pills.

2. Parenteral Route of Medication

A. Injections

A standard method to get medicines directly into the body is injections. Health providers choose this way when they need to administer drugs quickly and safely. Medicine gets into the bloodstream sooner because injections don't go through the digestive system.[5]There are different types of injections, and each route has its preferred advantage. i. Subcutaneous Injections
Subcutaneous injections use a small needle to deliver medicine into the fatty layer under the skin.[6] This method is gentle and works well for medications that need to be absorbed slowly, like insulin or blood thinners. Common areas for these injections include the upper arms, thighs, belly, or buttocks. The short and thin needle makes it less painful than other injections.ii. Intramuscular Injections
Intramuscular injections use a longer needle to deliver medicine directly into a muscle. This method allows the medication to enter the bloodstream quickly, making it ideal for vaccines or pain relief drugs.[7] 

Some Common Injection Sites include:

• Upper arm (shoulder muscle)
  
• Thigh
  
• Hip

These injections may feel slightly more uncomfortable because they go deeper into the tissue.iii. Intravenous (IV) Injections
Healthcare professionals use intravenous injections to deliver medications directly into a vein. This method is fast and effective because it immediately allows the medication to enter the bloodstream.[8] Intravenous injections are used for emergency treatments, fluids, antibiotics, or other essential medications. How?

• A healthcare professional inserts a small needle into a vein, usually in the arm.
• A thin tube is placed into the vein to keep it open.
• Medications are given through this tube, so a new needle isn’t needed each time.
• This method allows medications to be:
  • Delivered quickly for fast action.
  • Given slowly over time when continuous treatment is needed.

Other routes of medication administration include:

A.Topical route

This route involves applying medications to the skin. It is non-invasive and enters the skin, relieving various conditions like pain and arthritis. Some medications applied via this route include creams, ointments, and gels applied directly to the skin.The advantage of this administration route is that there are minimal systemic effects, and it targets specific areas. However, it is limited to surface issues and may not penetrate deeply enough.[10] A typical example is hydrocortisone cream for rashes.

B. Inhalation

Some medications are breathed in or delivered through inhalers or nebulisers. They are rapidly absorbed into the bloodstream and quickly relieve respiratory issues. However, it requires proper technique and may not be suitable for all patients.[11] Examples are asthma inhalers and corticosteroids like fluticasone for treating nasal congestion.

C. Vaginal route

The vaginal route of administration involves placing medications directly inside the vagina to treat gynaecological conditions.[12] This method is used for conditions like infections or hormonal imbalances and can be very effective because it delivers the medication right where it's needed. These medications come in forms like:

• Creams – e.g., Clotrimazole cream (used for yeast infections)
• Gels – e.g., Metronidazole gel (used for bacterial vaginosis)
• Tablets – e.g., Misoprostol tablet (used for cervical ripening or infections)
• Rings – e.g., NuvaRing (a contraceptive ring that releases hormones slowly)

The advantages and disadvantages of the various routes of administration are: 

1. Oral (By Mouth)

Advantages:

• Easy and convenient to take.
• Non-invasive and generally affordable.
  
  

Disadvantages:

• Absorption can vary depending on your stomach.
• Some medicines may be broken down by the liver before they work.

2. Sublingual (Under the Tongue)

Advantages:

• Fast-acting since it goes directly into your bloodstream.
• Helps you avoid breakdown by the liver.
  
  

Disadvantages:

• Only suitable for small doses.
• Some people may dislike the taste.
  
  

3. Rectal

Advantages:

• Useful when you can’t swallow pills (e.g., during vomiting or nausea).
  
  

Disadvantages:

• Absorption can be unpredictable.
• It may feel uncomfortable or invasive for some people.
  
  

4. Intravenous (IV – Into a Vein)

Advantages:

• It works very quickly.
• 100% of the medicine enters your bloodstream.

Disadvantages:

• A trained healthcare professional must set it up.
• Involves a needle, with a small risk of infection.

5. Intramuscular (IM – Into a Muscle)

Advantages:

• Faster absorption than under-the-skin injections.
• It can be used for long-lasting effects.

Disadvantages:

• It might cause pain or soreness.
• Absorption can vary based on your muscle mass and blood flow.
  
  

6. Subcutaneous (SC – Under the Skin)

Advantages:

• Often less painful than intramuscular injections.
• It provides steady, slow absorption over time.

Disadvantages:

• Only small amounts of medicine can be given this way.
• Absorption might not be consistent.
  
  

7. Topical (On the Skin)

Advantages:

• Easy to apply directly where it’s needed.
• Fewer side effects compared to systemic medications.
  
  

Disadvantages:

• Mostly applicable for local (not whole-body) problems.
• It can cause skin irritation in some people.
  
  

8. Vaginal

Advantages:

• It can treat both local and whole-body conditions.
• Avoids being broken down by the liver.
  
  

Disadvantages:

• Absorption may vary between individuals.
• May cause mild discomfort or irritation.
  
  

9. Inhalation (Breathing In)

Advantages:

• Starts working very quickly.
• Non-invasive and great for respiratory conditions like asthma.
  
  

Disadvantages:

• Requires correct technique to be effective.
• It may irritate the throat or airways.
  
  

Why It's Crucial to Follow the Prescribed Route of Administration:

• Wrong routes can be dangerous – Taking a medicine the wrong way (like injecting something meant for oral use) can cause serious harm or even be life-threatening.

• Effectiveness depends on the route – Some medications won’t work if not taken correctly (e.g., insulin must be injected, not swallowed).

• Dosing is route-specific – The body absorbs drugs differently depending on the route. Taking a medicine by the wrong path can lead to overdose or underdose.

• Side effects increase with incorrect use – Some routes protect your body (like bypassing the stomach); using the wrong one can cause irritation or organ damage.

• It's part of your treatment plan. Professionals choose the route to treat your condition safely and effectively. Ignoring it can delay healing or worsen symptoms.

Some Practical Tips for patients to follow include:

1. Follow instructions carefully. It is essential to adhere to your health provider’s instructions for optimal results.
2. Always ask. Please seek clarification if you do not understand how to take your medications.
3. Store your meds correctly. Make sure to keep medications at the right temperature to remain effective.

Conclusion

How effective your medications are depends on how much of the correct dose gets where needed. Using them via the proper route helps to prevent or minimise side effects and interactions with food and drugs. The advantages of each route sit heavily on the peculiarity of the patient’s case because this will determine what medication they should take and how safe it is for them. If you are currently on some drugs and you’re not entirely sure about the correct way to take them, it is important to seek clarification from your healthcare provider. Understanding the different routes of administration empowers you to take an active role in your treatment. Medication isn’t one-size-fits-all, and how you take it truly matters. Safe and effective use begins with the correct information and the proper guidance.

References

 1. Kim J, De Jesus O. Medication routes of administration. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 [cited 2025 Mar 25]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK568677/ 

2. Alagga AA, Pellegrini MV, Gupta V. Drug absorption. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 [cited 2025 Apr 15]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK557405/ 

3. Hua S. Physiological and pharmaceutical considerations for rectal drug formulations. Front Pharmacol [Internet]. 2019 Oct 16 [cited 2025 Apr 15];10:1196. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6805701/ 

4. Rn) OR for N (Open, Ernstmeyer K, Christman E. Chapter 18 administration of parenteral medications. In: Nursing Skills [Internet] [Internet]. Chippewa Valley Technical College; 2021 [cited 2025 Apr 15]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK593214/ 

5. Doyle GR, McCutcheon JA. 7. 3 Intradermal and subcutaneous injections. 2015 Nov 23 [cited 2025 Apr 15]; Available from: https://opentextbc.ca/clinicalskills/chapter/6-7-intradermal-subcutaneous-and-intramuscular-injections/ 

6. Polania Gutierrez JJ, Munakomi S. Intramuscular injection. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 [cited 2025 Apr 15]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK556121/ 

7. Rn) OR for N (Open, Ernstmeyer K, Christman E. Chapter 23 iv therapy management. In: Nursing Skills [Internet] [Internet]. Chippewa Valley Technical College; 2021 [cited 2025 Apr 15]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK593209/

8.  Drug routes of administration, their benefits, and risks [Internet]. 2023 [cited 2025 Mar 20]. Available from: https://www.medicalnewstoday.com/articles/routes-of-administration

9. Rn) OR for N (Open, Ernstmeyer K, Christman E. Chapter 1: Initiate IV therapy. In: Nursing Advanced Skills [Internet] [Internet]. Chippewa Valley Technical College; 2023 [cited 2025 Apr 15]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK594499/ 

10. Yu YQ, Yang X, Wu XF, Fan YB. Enhancing permeation of drug molecules across the skin via delivery in nanocarriers: novel strategies for practical transdermal applications. Front Bioeng Biotechnol [Internet]. 2021 Mar 29 [cited 2025 Apr 15];9:646554. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8039394/ 

11. Barnes PJ. Inhaled corticosteroids. Pharmaceuticals (Basel) [Internet]. 2010 Mar 8 [cited 2025 Apr 15];3(3):514–40. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4033967/ 

12. Alexander NJ, Baker E, Kaptein M, Karck U, Miller L, Zampaglione E. Why consider vaginal drug administration? Fertil Steril. 2004 Jul;82(1):1–12. Available from: https://pubmed.ncbi.nlm.nih.gov/15236978/ 

Disclaimer:
The information provided on this website is for general educational and informational purposes only. It is not intended to replace professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.

Published April 30, 2025