Doxycycline 100 mg is an oral antibiotic from the tetracycline class used to treat bacterial infections such as respiratory infections (bronchitis, pneumonia), urinary tract infections, skin infections (like acne or cellulitis), sexually transmitted infections (chlamydia, syphilis), gastrointestinal infections (like typhoid), and to prevent malaria in high-risk areas. It works by stopping bacteria from making the proteins they need to grow and survive, allowing the body to fight the infection.  

Common side effects include nausea, vomiting, diarrhea, stomach upset, headache, and sun sensitivity, while rare effects may include allergic reactions, liver problems, severe diarrhea, and tooth or bone discoloration in children. Doxycycline should not be taken by people allergic to it, children under 8 years, pregnant or breastfeeding women, or those with severe liver problems. It can be taken with or without food, but avoid dairy products, calcium-fortified drinks, antacids, or iron/magnesium/zinc supplements at the same time, leaving at least a 2-hour gap. 

Doxycycline 100 mg is an oral antibiotic medicine belonging to the tetracycline category, and this medicine is used to prevent and treat conditions like: 

1. Respiratory tract infections (like bronchitis or pneumonia) 
2. Urinary tract infections (UTIs) 
3. Skin infections (like acne or cellulitis) 
4. Sexually transmitted infections (like chlamydia or syphilis) 
5. Gastrointestinal infections (like typhoid or bacterial diarrhea) 
6. Prevention of malaria in people traveling to high-risk areas    

1. Take this medicine exactly as prescribed by your doctor, at the same time each day. 
2. Do not stop taking this medicine without your doctor’s approval, even if you feel better. 
3. If you forget to take this medicine, take it as soon as you remember. If it’s almost time for your next dose, skip the missed dose. 

More Common  

1. Nausea 
2. Vomiting 
3. Diarrhea 
4. Stomach pain or upset 
5. Loss of appetite 
6. Headache 
7. Sun sensitivity (skin may burn more easily in sunlight)     

Less Common

1. Allergic reactions (rash, swelling, difficulty breathing) 
2. Severe diarrhea due to C. difficile infection 
3. Liver problems (yellowing of skin/eyes, dark urine) 
4. Changes in blood counts (low platelets or white blood cells) 
5. Tooth or bone discoloration in children   

Doxycycline works by stopping bacteria from making proteins they need to grow and multiply. Without these proteins, the bacteria cannot survive, which allows your body to fight off the infection and heal. 

Allergy or hypersensitivity

If you are allergic to doxycycline or other tetracycline antibiotics, taking it may cause serious reactions such as rash, swelling of the face or lips, or difficulty breathing. Stop the medicine immediately and seek medical help. 

Children

If children under 8 years take doxycycline, it may affect teeth and bone development, causing permanent tooth discoloration or weaker bones. Avoid giving this medicine to young children unless a doctor specifically prescribes it. 

Pregnancy and Breastfeeding

If a pregnant or breastfeeding woman takes doxycycline, it may harm the baby or infant, affecting bone and tooth development. Do not take this medicine unless your doctor advises it.

Liver problems

If someone with severe liver disease takes doxycycline, it may worsen liver function, leading to tiredness, jaundice, or other liver-related issues. Inform your doctor, who may adjust the dose or prescribe a safer alternative.  

Doxycycline can be taken with or without food but taking it with a meal may help reduce stomach upset. You should avoid taking it at the same time as dairy products like milk, cheese, or yogurt, as well as calcium-fortified drinks, because they can reduce how well the medicine works. Do not take it together with antacids or supplements containing iron, magnesium, or zinc; leave at least a 2-hour gap. Other common foods or drinks usually do not interfere with doxycycline. 

Avoid taking Doxycycline 100 mg with the following medicines, as it may increase or decrease the desired effect, or in worse cases, it could be fatal: 

IUPAC (International Union of Pure and Applied Chemistry)/ Chemical name

(4S,4aR,5S,5aR,6R,12aR)-4-(dimethylamino)-1,4,4a,5,5a,6,11,12a-octahydro-3,5,10,12,12a-pentahydroxy-6-methyl-1,11-dioxo-2-naphthacenecarboxamide hydrochloride 

Daily dose

Take Doxycycline 100 mg exactly as your doctor recommends. The dose may change based on your condition and how well you respond. Do not take more than prescribed without consulting your doctor. 

Missed Dose

If you forget to take your medicine, take the medication as soon as you remember. If it’s nearly time for your next dose, skip the missed one and continue with your regular schedule. Always consult the doctor before making any changes to your dosage. 

Overdose

It is not recommended to take more than 300 mg doxycycline per day, as it may cause severe overdose symptoms like nausea, vomiting, headache, tremors, restlessness, and rapid heartbeat. 

1. Store the medicine at room temperature 
2. Keep away from sunlight and moisture 
3. Keep out of reach of children  

What are the uses of Doxycycline 100 mg? 

Doxycycline 100 mg tablet is used to treat bacterial infections such as respiratory infections (bronchitis, pneumonia), urinary tract infections, skin infections (like acne or cellulitis), sexually transmitted infections (chlamydia, syphilis), gastrointestinal infections (like typhoid), and to prevent malaria in high-risk areas. 

How does Doxycycline 100 mg work? 

Doxycycline 100 mg works by stopping bacteria from making the proteins they need to grow and survive. Without these proteins, the bacteria cannot multiply, which allows your body to fight off the infection and heal. 

Who should not take Doxycycline 100 mg? 

Doxycycline 100 mg should not be taken by people who are allergic to it or other tetracycline antibiotics, children under 8 years (can affect teeth and bones), pregnant or breastfeeding women (may harm the baby or infant), and people with severe liver problems. 

What class of medicine is Doxycycline? 

Doxycycline belongs to the tetracycline class of antibiotics, which work by stopping bacteria from growing and multiplying. 

Can Doxycycline 100 mg be taken during pregnancy? 

Doxycycline 100 mg is not recommended during pregnancy because it may affect the baby’s bone and tooth development. It should only be taken if a doctor specifically prescribes it after weighing the risks and benefits. 

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3. PubChem. Doxycycline Hydrochloride [Internet]. Nih.gov. PubChem; 2025 [cited 2025 Dec 9]. Available from