📄 chemistry

Stability of South African commercial and extemporaneously prepared cannabidiol (CBD) topical oil-in-water emulsions

This study evaluates the stability of South African commercial and extemporaneously prepared CBD topical oil-in-water emulsions, finding that while light and heat generally degrade CBD, commercially available gels and high-viscosity Pickering emulsions (stabilized by Aerosil® R974) offer superior stability compared to other formulations like tissue oils.

Original authors: Alyson Bennett, Roderick B. Walker

Published 2026-08-03

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Alyson Bennett, Roderick B. Walker

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you are a chef trying to bake the perfect cake, but instead of flour and sugar, your main ingredient is a delicate, temperamental spice that hates heat and gets nervous in the sunlight. This is the world of Cannabidiol, or CBD, a popular ingredient found in lotions and oils that people use to soothe sore muscles or calm skin. In South Africa, these products are strictly regulated to ensure they are safe and contain only tiny, legal amounts of CBD without any of the "high" associated with cannabis. However, there's a catch: CBD is like a shy guest at a party who melts away if the room gets too warm or if the lights are too bright. If the CBD breaks down before you even use the product, the lotion is just expensive water. This research dives into the science of keeping this "shy guest" safe inside different types of creams and oils, testing how well various recipes protect the ingredient from the everyday heat and light of a South African summer.

The scientists at Rhodes University decided to play a game of "survival of the fittest" with CBD. They gathered a lineup of commercially available CBD products—like body lotions, hand creams, and gels bought from local pharmacies—and mixed up their own special versions in the lab, known as "extemporaneously prepared" formulations. Think of these homemade versions as experimental recipes where the scientists swapped out ingredients to see which combination created the strongest shield for the CBD. They tested these mixtures under three different conditions: sitting in a cool, dark cabinet (the safe zone), sitting on a sunny windowsill (the light trap), and baking in a warm oven set to 37°C (the heat trap). They wanted to see which formulation kept the CBD intact the longest and which ones let it degrade, or fall apart, the fastest.

The results were like a race where the starting line was full of promise, but the finish line showed some surprising winners and losers. The study found that heat and light are the ultimate villains for CBD stability. When the products were exposed to light or heated up to 37°C, the CBD started to break down much faster, like ice cream melting on a hot day. Among the store-bought products, the gel was the clear champion. It held onto its CBD the best, even when things got warm. The researchers suspect this is because the gel is so thick and sticky (high viscosity) that it acts like a fortress, making it hard for the damaging effects of heat and light to reach the CBD trapped inside. In contrast, the tissue oil was the biggest loser. It lost a massive amount of its CBD, especially when stored at 37°C, likely because oil is thin and offers very little protection against the elements.

The homemade experiments offered some fascinating insights into how to build a better shield. The scientists created different types of mixtures, including one called a Pickering emulsion. You can think of this as a special recipe where tiny solid particles (called Aerosil® R974) act like tiny bricks, building a sturdy wall around the oil droplets containing the CBD. This "brick wall" structure turned out to be incredibly effective. The Pickering emulsion showed better stability than the other homemade creams, holding its ground even at 37°C. However, there was a trade-off: while this "brick wall" cream was great at protecting the CBD, it was also very thick and hard to spread on the skin, especially when warm. The other homemade creams were easier to spread but didn't protect the CBD quite as well as the gel or the Pickering emulsion.

Ultimately, the paper suggests that if you want a CBD cream that stays effective in a hot climate, you need a thick, sturdy formula. The commercial gel proved that high thickness can slow down degradation, and the lab-made Pickering emulsion showed that using solid particles to build a protective structure is a promising way to make stable creams. However, the study also highlights a challenge: making a product that is both super-stable and easy to spread is difficult. The tissue oil, which was easy to spread, failed miserably at keeping the CBD safe. So, while we haven't found the perfect, magic potion yet, this research gives us a clear map: to keep CBD from disappearing, we need to build thicker, stronger barriers around it, perhaps using those tiny "brick" particles, even if it means the cream feels a bit heavier on the skin.

Technical Summary: Stability of South African Commercial and Extemporaneously Prepared Cannabidiol (CBD) Topical Oil-in-Water Emulsions

Problem Statement
In South Africa, topical formulations containing cannabidiol (CBD) are regulated as Schedule 0 products under the Medicines and Related Substances Act, requiring low CBD content and negligible THC (<0.001%). However, the reliability of these products is compromised by inconsistent CBD content, mislabeling, and degradation. Previous studies have highlighted that clinical trials for topical CBD often suffer from bias and small sample sizes, while commercial quality testing reveals significant discrepancies between labeled and actual CBD content. Furthermore, CBD is susceptible to degradation via light exposure and elevated temperatures, leading to product inactivity and consumer mistrust. There is a lack of standardized data regarding the stability of South African commercial CBD topicals compared to extemporaneously prepared formulations under local "in-use" conditions.

Methodology
The study evaluated the physical properties and stability of a selection of commercially available South African CBD topicals (body lotion, hand cream, muscle joint cream, tissue oil, and gel) alongside extemporaneously prepared oil-in-water (o/w) emulsions.

Formulations: Four extemporaneous formulations were developed to mimic commercial aqueous creams: a standard aqueous cream, a gel emulsion, an emulgel, and a Pickering emulsion stabilized with Aerosil® R974 (partially hydrophobic silica). These were prepared using cold-processing techniques at room temperature (22°C).
Characterization: Physical properties were assessed including viscosity (Brookfield viscometer), dynamic yield stress and shear-thinning behavior (Anton Paar rheometer), spreadability (parallel-plate method at 22°C, 25°C, 30°C, and 35°C), and Zeta potential (ZP) using a 10 mM NaCl solution.
Analytical Method: A new extraction and High-Performance Liquid Chromatography (HPLC) method was developed and validated according to ICH guidelines (Q2(R2)) to quantify CBD content. The method utilized a C18 column with UV detection at 228 nm.
Stability Testing: Samples were subjected to three conditions over 12 weeks:
1. Room temperature (22°C) in the dark.
2. Room temperature (22°C) with light exposure (simulating benchtop use).
3. Elevated temperature (37°C) in the dark (simulating storage in warm climates or body heat).
Data Analysis: CBD degradation was modeled using first-order reaction kinetics to determine rate constants ( $k$ ).

Key Results

Physical Properties:
- Viscosity and Yield Stress: The Pickering emulsion (4.5% Aerosil® R974) exhibited the highest viscosity (5,100,000 cP) and dynamic yield stress (215.03 Pa) among all tested samples. The commercial gel was the most viscous commercial product (4,595,000 cP). The tissue oil was a low-viscosity Newtonian fluid.
- Spreadability: Temperature significantly affected spreadability. While most creams and lotions became more spreadable at 35°C, the high-viscosity gel and Pickering emulsion showed decreased spreadability as temperature increased. Specifically, the Pickering emulsion exhibited lower spreadability at 35°C compared to the other extemporaneously prepared o/w emulsion formulations.
- Zeta Potential: Values ranged from -13.33 mV to -30.73 mV. The Pickering emulsion showed a ZP of -25.50 mV, attributed to the silanol groups of Aerosil® R974 and the absence of non-ionic surfactants.
CBD Stability:
- Degradation Factors: Light exposure and elevated temperature (37°C) significantly increased CBD degradation rates across all formulations.
- Commercial Products: The commercial gel demonstrated the best stability, with the lowest degradation rates under all conditions. The tissue oil showed the poorest stability, losing 90.4% of CBD content after 12 weeks at 37°C. The hand cream and body lotion showed moderate stability, with the hand cream retaining more CBD than the body lotion at 37°C, potentially due to higher viscosity and shea butter content.
- Extemporaneous Formulations: Generally, extemporaneous formulations degraded faster than commercial products. However, the Pickering emulsion exhibited a slower degradation rate ( $k = 0.0156$ day $^{-1}$ at 37°C in the dark) compared to other extemporaneous o/w emulsions ( $k = 0.0170$ and $0.0174$ day $^{-1}$ ).
- Viscosity Correlation: Higher viscosity formulations (gel and Pickering emulsion) generally correlated with slower degradation rates, likely due to reduced penetration of pro-oxidants to the CBD entrapped in oil droplets.

Significance and Claims
The paper concludes that storage temperature and light exposure are critical drivers of CBD degradation in topical formulations, particularly those with lower viscosity and fewer antioxidants. The study validates that:

Commercial Superiority: Commercially available gels offer superior CBD stability compared to other tested commercial products and extemporaneous formulations, likely due to specific excipient combinations (including antioxidants) and high viscosity.
Pickering Emulsion Potential: The Pickering emulsion, stabilized with Aerosil® R974, offers a viable alternative for extemporaneous preparation. It provides high viscosity and improved CBD stability at 37°C compared to other cold-processed o/w emulsions, despite having lower spreadability at elevated temperatures.
Formulation Design: The use of excipients like Aerosil® R974 can create a stable, high-viscosity o/w emulsion that mimics commercial cream attributes while improving CBD stability under thermal stress.
Limitations: The inclusion of antioxidants (like rosmarinic acid in other studies) did not necessarily enhance stability in all contexts, suggesting that physical barriers (viscosity, droplet packing) may be as critical as chemical stabilization.

The authors emphasize that while the Pickering emulsion showed promise, further studies are required to fully understand the relationship between high viscosity, low spreadability, droplet size, and oxidation rates in CBD formulations. The research underscores the need for rigorous quality control and appropriate packaging (opaque containers) to ensure product efficacy in the South African market.

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