1. What Is a Capsule and Why It Matters
Capsules are small containers used to deliver medicine. They hold powders, granules, oils, or liquids. Unlike tablets, capsules usually have a smooth outer shell that makes them easier to swallow. They also help mask unpleasant tastes and allow for better control of drug release.
From prescription drugs to daily vitamins, capsules are everywhere in modern healthcare. Understanding their types can help you choose the best one for your product or treatment.
2. Classification of Capsules by Structure
A. Hard Gelatin Capsules (HGCs)
Hard gelatin capsules are the most common type. They are made of animal-based gelatin and consist of two parts—a body and a cap. These capsules are typically filled with dry substances like powders or granules.
They dissolve quickly in the stomach, releasing the contents for absorption. They are affordable and easy to manufacture. However, they are sensitive to humidity and unsuitable for liquids unless specially modified.
B. Soft Gelatin Capsules (Softgels)
Softgels have a one-piece, flexible shell made from gelatin mixed with glycerin or sorbitol. They are ideal for holding oils, vitamins, and other fat-soluble compounds.
Softgels are popular in the supplement industry due to their smooth texture and fast absorption. However, they require more complex equipment and precise temperature control during production.
C. Vegetarian Capsules
Vegetarian capsules are made from HPMC (hydroxypropyl methylcellulose) or pullulan (a fermented tapioca derivative). They are used when animal-derived ingredients are not acceptable—for example, for vegan, halal, or kosher products.
These capsules have similar mechanical strength to gelatin capsules but offer better stability in hot and humid climates. They dissolve more slowly than gelatin, making them suitable for extended or delayed-release applications.
D. Enteric-Coated Capsules
Enteric-coated capsules have a special layer that resists stomach acid. They only dissolve once they reach the intestine. This coating protects sensitive ingredients like probiotics or drugs that might irritate the stomach lining.
Enteric coatings can be applied to both hard and soft capsules. They are essential for drugs that require targeted delivery or delayed action.
E. Liquid-Filled Capsules
Some capsules, especially softgels or modified hard capsules, are designed to hold liquids. This form allows precise dosing of potent or unstable ingredients like essential oils, hormones, or plant extracts.
Liquid-filled capsules need tight sealing and advanced manufacturing to prevent leakage. Their main advantage is faster absorption and higher bioavailability.
3. Classification by Fill Type
Capsules can contain different kinds of material:
- Powders – most common in traditional pharmaceuticals
- Granules or pellets – used for controlled or sustained release
- Liquids and oils – common in softgels and liquid-filled capsules
- Semi-solids or pastes – often used in nutritional formulas
- Combinations – some capsules use multi-phase filling, like beads and liquids together
Each fill type affects the way the drug is absorbed and how the body processes it.
4. Capsule Shell Materials: What Are Capsules Made Of?
A. Animal-Based Gelatin
This is the traditional material for capsules. Gelatin is derived from collagen in bovine or porcine skin and bones. It is inexpensive, widely available, and dissolves well in the stomach.
However, it’s not suitable for vegetarians, vegans, or people with religious dietary restrictions.
B. Plant-Based Shells (Vegetarian Capsules)
HPMC is the most popular alternative. It’s stable across a wide range of temperatures and doesn’t rely on animal products. Pullulan is another plant-based option with excellent oxygen barrier properties.
Vegetarian capsules are more expensive to produce, but they meet growing consumer demand for clean-label and animal-free products.
C. Specialized Coatings
Enteric polymers and starch-based blends are also used to create capsules with specific release profiles. Some seaweed-based capsules (carrageenan) are in development but less common.
5. Hard vs Soft Gelatin Capsules: Key Differences
Each type has its place. Softgels are great for quick absorption and oil-based nutrients. Hard capsules are versatile and cost-effective for dry materials.
6. Other Capsule Forms
- Caplets: Tablet-capsule hybrids; shaped for easy swallowing
- Modified-release capsules: Designed to release drugs over time
- Dual-release or multi-chamber capsules: Combine two types of ingredients in one dose
These innovations help tailor drug delivery to meet specific medical needs.
7. Capsule Sizes and Shapes
Capsules come in standardized sizes, from 000 (largest) to 5 (smallest). The size you choose depends on:
- Dosage requirements
- Type of material inside
- Swallowability
- Filling machine compatibility
Most dietary supplements use sizes 0 or 00, while pharmaceuticals may use 1 or 2.
8. Applications in Medicine and Supplements
Different types of capsules suit different industries:
- Prescription medications – antibiotics, anti-inflammatory drugs
- Nutritional supplements – vitamins, minerals, fish oils
- Probiotics – often in enteric or vegetarian capsules
- Herbal extracts – turmeric, ginseng, or CBD in softgels or HPMC capsules
- Clinical trials – custom formulations with strict quality needs
Capsules can improve taste masking, shelf life, and even brand identity through color and printing.
9. Choosing the Right Capsule
When choosing a capsule type, consider:
- The physical and chemical nature of your product
- Your target consumer (vegan, elderly, children)
- Required release profile (immediate, delayed, extended)
- Storage and transport conditions
- Budget and production scale
Manufacturers must also follow Good Manufacturing Practices (GMP) to ensure quality and safety.
10. Capsule Manufacturing and Filling Equipment
Capsule production involves two main stages: shell manufacturing and capsule filling. Depending on the type of capsule (hard or soft), the machinery used varies greatly in function, precision, and output.
A. Hard Capsule Filling Machines
Hard capsules are usually pre-manufactured and shipped empty to pharmaceutical or supplement companies. These companies then use capsule filling machines to dose and close the capsules.
Common Filling Methods:
- Powder filling – most common
- Pellet filling – for sustained or dual-release
- Liquid filling (with sealing) – for potent extracts or oils
Machine Types:
- Semi-automatic Capsule Filling Machines – good for mid-size batches
- Fully Automatic Capsule Filling Machines – used in large-scale pharmaceutical production; can fill, close, and eject thousands of capsules per hour
These machines can be adjusted for capsule size (000 to 5) and support multiple dosing stations. Modern models often include sensors and weight control for high accuracy and compliance with GMP standards.
B. Softgel Manufacturing Machines
Soft gelatin capsules require a completely different process. Unlike hard capsules, softgels are formed, filled, and sealed simultaneously using rotary die encapsulation machines.
Functions:
- Prepare the gelatin ribbon (mixed with plasticizer)
- Pump the fill material (oil, extract, etc.)
- Form capsules in rotary dies with heat and pressure
- Cool, trim, dry, and polish the softgels
Softgel machines are highly specialized and often run in climate-controlled cleanrooms. Their advantages include excellent seal integrity, uniform dosing, and attractive capsule appearance.
C. Additional Equipment in Capsule Production
- Polishing Machines – clean capsules of any powder residue or oil film
- Inspection Systems – optical or laser-based machines to reject defective capsules
- Printing Machines – imprint dosage, branding, or batch codes
- Sorting and Counting Systems – ensure consistent packaging downstream
11. Common FAQs
Q: What are capsules made of?
Capsules are made of gelatin (animal-based) or HPMC/pullulan (plant-based). They can also include plasticizers, coatings, and colorants.
Q: What’s the difference between a tablet and a capsule?
Tablets are compressed powders. Capsules are containers that hold medicine inside a shell. Capsules are often easier to swallow and faster to absorb.
Q: Are all capsules vegan?
No. Only capsules made from HPMC or pullulan are vegan. Gelatin capsules come from animals.
Q: Can capsules be opened and mixed?
Some can. Hard capsules may be opened if approved by a doctor. Softgels cannot be opened without losing content or stability.
Q: Are capsules better than tablets?
It depends. Capsules are easier to swallow and absorb faster. Tablets are more stable and often cheaper.
12. Conclusion: Capsule Variety Powers Modern Healthcare
Capsules are more than just a pill shape—they are a delivery system that can be tailored to different drugs, users, and health goals. Understanding the types of capsules helps healthcare providers, supplement makers, and consumers make better decisions.
From softgels filled with omega-3 to vegetarian capsules carrying herbal blends, today’s capsule technology continues to evolve with science, safety, and user needs in mind.