What are the different types of transdermal drugs?

October 11, 2025 •

5 min read

The market for transdermal drug delivery systems is experiencing significant growth, projected to reach hundreds of billions of dollars in the coming decade, driven by demand for non-invasive and patient-friendly treatments. Understanding what are the different types of transdermal drugs available is key for both patients and healthcare providers to appreciate the versatility and benefits of this delivery method.

Quick Summary

Different types of transdermal drugs include passive systems like patches, gels, and sprays, as well as enhanced systems using physical or electrical methods. These delivery systems offer advantages such as steady dosing and avoiding the digestive tract, catering to a wide range of medical needs.

Key Points

First-generation systems use passive diffusion: Rely on a drug's inherent properties to slowly absorb through the skin, suitable for small, potent, lipid-soluble drugs.
Common delivery forms include patches, gels, and sprays: Patches offer highly controlled, sustained release, while gels and sprays provide easier application for systemic absorption.
Second-generation methods enhance absorption: These utilize chemical enhancers to modify the skin's barrier or physical enhancers like electrical currents (iontophoresis) or sound waves (ultrasound) to boost drug penetration.
Third-generation innovations overcome delivery barriers: Advanced systems like microneedle patches create micro-channels in the skin, enabling the delivery of larger molecules that cannot be absorbed passively.
Nanotechnology plays a crucial role: Nanocarriers like liposomes and nanoemulsions encapsulate drugs to improve solubility and provide targeted, controlled release in advanced transdermal systems.
Transdermal delivery avoids first-pass metabolism: By bypassing the digestive system and liver, transdermal drugs avoid degradation and offer more consistent plasma levels than many oral medications.
Factors like skin hydration and temperature affect absorption: The integrity of the skin, its temperature, and moisture levels can influence how well and how quickly a drug is absorbed transdermally.

Transdermal drug delivery is a method of medication administration where drugs are absorbed through the skin and into the bloodstream for systemic effects. Unlike traditional oral medication, this route bypasses the gastrointestinal system and avoids 'first-pass' metabolism by the liver, which can degrade certain drugs and reduce their effectiveness. Over the decades, these systems have evolved significantly, moving from simple, passive methods to sophisticated, active technologies that enhance drug absorption.

First-Generation Transdermal Systems

First-generation systems rely primarily on a drug's intrinsic physicochemical properties to allow for passive diffusion through the skin's outermost layer, the stratum corneum. These systems work best for potent, low-molecular-weight, and lipid-soluble drugs.

Transdermal Patches

Medicated adhesive patches are the most common form of first-generation transdermal drug. They are engineered to deliver a precise, controlled dose of medication over a set period, from hours to a week.

Common types of patches include:

Single-Layer Drug-in-Adhesive: The drug is directly mixed into the adhesive layer that adheres to the skin. This simple design is cost-effective and provides a steady release rate.
Multi-Layer Drug-in-Adhesive: These patches use multiple layers of adhesive to create more complex release profiles. They can deliver an initial burst of medication followed by a sustained release or combine different drugs.
Reservoir Patches: These contain a separate compartment with the drug in a liquid or gel form, which is released through a rate-controlling membrane. They are ideal for potent drugs requiring very precise dosage control.
Matrix Patches: The drug is dispersed throughout a polymer matrix that is in direct contact with the skin. Release occurs as the drug diffuses out of the matrix.
Vapor Patches: These release volatile substances that can be absorbed through the skin or via inhalation.

Examples of medications delivered via transdermal patches include nicotine for smoking cessation, fentanyl and buprenorphine for chronic pain, and hormones like estrogen for replacement therapy.

Topical Gels, Creams, and Sprays

These semi-solid or liquid formulations are applied to the skin and absorbed for systemic effect, though the absorption rate is often less controlled than with patches. They are valued for their ease of application.

Gels: Semi-solid systems that are easy to spread over large areas. Testosterone gels are a common example used for hormone replacement.
Sprays: Liquid formulations that are misted onto the skin for rapid absorption. Estradiol sprays are used for hormone delivery.

Second-Generation Transdermal Systems

These systems employ additional methods to enhance skin permeability, expanding the range of drugs that can be delivered transdermally beyond those suitable for passive diffusion.

Chemical Enhancers

Chemical enhancers are substances that reversibly increase the skin's permeability by altering the structure of the stratum corneum. This allows a wider variety of drugs to be delivered.

Common examples include alcohols, fatty acids, and some solvents, which can increase drug solubility and partitioning into the skin.

Physical Enhancers

Physical methods use energy to temporarily increase skin permeability.

Iontophoresis: This technique uses a low-level electrical current to drive charged drug molecules across the skin. It offers a more controlled delivery rate and can be used for both charged and uncharged molecules. LidoSite® was an early example for delivering lidocaine.
Electroporation: This method uses high-voltage electrical pulses for very short durations to create temporary pores in the skin's lipid bilayers. It can deliver larger molecules, but carries a risk of cell damage.
Ultrasound (Sonophoresis): Uses high-frequency sound waves to disrupt the skin barrier and increase permeability. Low-frequency ultrasound is generally more effective.

Third-Generation Transdermal Systems

These represent the latest advancements, using advanced technologies to target the stratum corneum with minimal invasion, making transdermal delivery possible for macromolecules like proteins and vaccines.

Microneedle Patches

Microneedles are an array of tiny needles that painlessly pierce the stratum corneum to create microchannels, bypassing the skin's main barrier.

They can deliver larger molecules, offer faster absorption, and reduce dosing frequency.
Various types exist, including solid, hollow, and dissolving microneedles that are coated or encapsulate the drug.

Nanocarriers and Vesicular Systems

Nanotechnology allows for the encapsulation of drugs within tiny carriers, improving their stability, solubility, and targeted delivery.

Nanoparticles: Solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) can deliver drugs with high bioavailability and control.
Vesicular Carriers: Systems like liposomes, ethosomes, and niosomes are phospholipid-based carriers that can encapsulate drugs and enhance permeation. Ethosomes, for example, incorporate ethanol to act as a permeation enhancer.
Nanoemulsions: These are fine oil-in-water dispersions that improve drug penetration and controlled release.

Comparison of Transdermal Drug Delivery Types


Feature	First-Generation (Patches, Gels)	Second-Generation (Chemical/Physical Enhancers)	Third-Generation (Advanced)
Delivery Mechanism	Passive diffusion driven by drug's properties.	Active enhancement via chemical or physical means (electricity, sound waves).	Micro-invasive disruption of stratum corneum or targeted delivery with nanocarriers.
Drug Suitability	Small, potent, lipid-soluble molecules with low daily dose requirements.	Broader range of drugs, including some larger or less lipophilic compounds.	Large molecules like proteins, peptides, and vaccines.
Control over Release	Generally good, sustained release (especially patches).	Highly controlled, often patient-adjustable delivery rates (e.g., iontophoresis).	Highly controlled and targeted release, often with rapid onset of action (e.g., microneedles).
Complexity	Relatively simple, with patches requiring specialized manufacturing.	More complex, involving external devices (e.g., iontophoresis units) or special formulations.	Highly complex, involving microneedle fabrication or advanced nanotechnology.
Invasiveness	Non-invasive.	Non-invasive, though some methods can cause local irritation.	Minimally invasive (microneedles) or non-invasive (nanocarriers).
Patient Convenience	High (e.g., once-daily or weekly patch application).	Moderate (requires external device and potential longer application time).	High (e.g., painless, self-administered patches).

Conclusion

Transdermal drug delivery has evolved significantly from passive methods like patches and gels to advanced technologies that can actively enhance absorption or bypass the skin's barrier entirely. The choice of transdermal system depends on the drug's properties and the therapeutic goal. First-generation systems are simple and effective for many small-molecule drugs, while second-generation approaches use chemical or physical boosters to broaden the range of deliverable medications. The cutting-edge third-generation technologies, such as microneedles and nanocarriers, promise to deliver even larger, more complex molecules with unprecedented control and precision, opening new possibilities for patient care. As research continues to advance, the transdermal route is set to become an even more prominent and versatile player in modern medicine, offering convenience, safety, and improved patient outcomes.

For more in-depth scientific information on the mechanisms and future of transdermal drug delivery, you can explore detailed reviews like this one from the National Institutes of Health (NIH).

Frequently Asked Questions

A reservoir patch holds the drug in a separate liquid or gel compartment controlled by a membrane, ensuring a precise release rate. In contrast, a matrix patch has the drug dispersed within a polymer matrix that is in direct contact with the skin.

No, standard passive transdermal patches are typically ineffective for large molecules. The skin's outermost layer, the stratum corneum, is a strong barrier that generally limits passive diffusion to molecules under 500 Daltons. Advanced methods like microneedles are required for larger drugs.

Iontophoresis patches use a mild electrical current to actively push charged drug molecules into the skin. This allows for a more controlled and often faster delivery rate than passive diffusion, and can deliver drugs that would not otherwise penetrate the skin effectively.

Microneedle patches use an array of tiny needles to create micro-channels in the stratum corneum. This allows the drug to bypass the skin's primary barrier and be delivered more effectively into the deeper layers and bloodstream, even for larger molecules.

Transdermal patches for pain management often contain analgesics like fentanyl or buprenorphine. These are used for managing chronic and severe pain by providing a continuous, controlled release of medication.

Avoiding first-pass metabolism, where the liver processes and potentially degrades a drug after absorption from the gut, is a major advantage. This means a higher percentage of the drug reaches systemic circulation, often resulting in more stable and consistent blood levels.

Yes, the anatomical location of a patch can affect absorption. Factors like skin thickness, temperature, and blood flow vary across the body, which influences the rate and amount of drug absorbed. For example, absorption is generally faster in areas with thinner skin.