Liquid Natural Health Products: Key Formulation Considerations

Liquid natural health products (NHPs) are becoming an increasingly popular option for consumers and product developers because they can offer convenient dosing and flexible formulation options. However, selecting a liquid dosage form should not be based on consumer preference alone. A successful liquid NHP must be chemically and physically stable, microbiologically controlled, palatable, manufacturable, and compatible with its packaging.

When Does a Liquid Formulation Offer an Advantage?

A liquid formulation can be particularly useful when the required dose is relatively small, and the ingredients have good solubility or can be reliably suspended or emulsified. Liquids can also be advantageous for products intended for individuals who have difficulty swallowing conventional solid dosage forms.

For example, vitamin D3 in an oil-based liquid can be a logical formulation because vitamin D3 is fat-soluble and can be incorporated into an appropriate lipid vehicle. Similarly, liquid iron products may be attractive when the target consumer has difficulty swallowing tablets/capsules or when a lower, adjustable dose is desired.

Botanical extracts can also be suitable for liquids when the extract is compatible with the selected vehicle. Tincture-style products, glycerin-based botanical preparations, and certain water-soluble botanical extracts are examples where a liquid format may provide a practical delivery system.

By contrast, a powder may be preferable when the ingredients are poorly soluble, chemically unstable in the presence of water, difficult to preserve, or required at a high dose. A 5 g botanical powder, for example, may be considerably more practical than attempting to incorporate the same quantity into a small-volume liquid.

What Should Be Considered During Liquid Formulation?

1. Solubility and dispersion are usually the starting point: Each medicinal ingredient and excipient should be evaluated for its solubility, pH dependence, interaction with other ingredients, and tendency to precipitate. An ingredient that appears soluble individually may become insoluble when combined with other components.

2. pH is equally important: The formulation pH can affect solubility, chemical stability, preservative performance, colour, flavour, and compatibility with other ingredients. Buffer selection should therefore be based on the requirements of the complete formulation rather than the properties of a single ingredient.

3. Microbiological control is a major consideration: Unlike a dry powder, an aqueous liquid can provide an environment that supports microbial growth. Formulators may need to consider water quality, water activity, preservative selection, manufacturing hygiene, container closure, and preservative effectiveness. 

4. Physical stability must also be demonstrated: A liquid may develop precipitation, sedimentation, phase separation, viscosity changes, colour changes, or loss of dispersibility during storage. For suspensions and emulsions, the formulation must remain sufficiently uniform so that the consumer receives an appropriate dose throughout the product's use. Homogeneity and microbiological control are recognized as important stability considerations for liquid dosage forms.

5. Taste and mouthfeel can determine consumer acceptance: Ingredients such as minerals, certain botanical extracts, amino acids, and concentrated vitamins may produce bitterness, metallic notes, astringency, odour, or aftertaste. Flavour systems, sweeteners, organic acids, masking agents, and suitable vehicles may therefore be necessary. However, these ingredients must be selected within the applicable regulatory and formulation requirements.

6. Packaging is part of the formulation: Light-sensitive ingredients may require light-protective containers, while oxygen-sensitive formulations may benefit from appropriate oxygen-control strategies. The closure system should also be evaluated for compatibility, leakage, sorption, and protection against contamination. 

Key Questions Before Selecting a Liquid Dosage Form

A practical way to determine whether a liquid is the most appropriate dosage form is to consider the following questions:

1. Can the target dose be delivered conveniently in a reasonable volume?

2. Can the ingredients remain soluble, suspended, or emulsified throughout shelf life?

3. Can microbial growth be adequately controlled?

4. Can taste, odour, colour, and mouthfeel be made acceptable?

5. Can the formulation remain stable in its intended packaging under the proposed storage conditions?

If the answers to these questions are favourable, a liquid dosage form may provide meaningful advantages. Otherwise, a powder, capsule, or tablet may offer a more robust formulation solution.

Ultimately, developing a successful liquid NHP is not simply a matter of dissolving ingredients in water. It is a formulation exercise that requires consideration of chemistry, microbiology, physical stability, sensory characteristics, manufacturing capability, packaging, and regulatory requirements from the beginning of development. The best dosage form is therefore not the one that looks most convenient on paper, but the one that consistently delivers a safe, stable, acceptable, and appropriately dosed product throughout its intended shelf life.

References 

1. Health Canada. Quality of Natural Health Products Guide. This guidance covers NHP quality expectations, including microbial quality, antimicrobial effectiveness, and stability. 

2. Health Canada. Good Manufacturing Practices Guide for Natural Health Products (GUI-0158): Stability Period. Health Canada — NHP GMP Guide

3. Vázquez-Blanco, S., González-Freire, L., Dávila-Pousa, M. C., & Crespo-Diz, C. (2018). pH determination as a quality standard for the elaboration of oral liquid compounding formula. Farmacia Hospitalaria, 42(6), 221-227.

4. Andrews, D., Salunke, S., Cram, A., Bennett, J., Ives, R. S., Basit, A. W., & Tuleu, C. (2021). Bitter-blockers as a taste masking strategy: a systematic review towards their utility in pharmaceuticals. European Journal of Pharmaceutics and Biopharmaceutics, 158, 35-51.

5. Sanjay, L. R., Ashokbhai, M. K., Ghatole, S., Roy, S., Kashinath, K. P., & Kaity, S. (2025). Strategies for beating the bitter taste of pharmaceutical formulations towards better therapeutic outcomes. RSC Pharmaceutics, 2(1), 59-81.