The term pH refers to the relative amount of hydrogen ions in an environment. Therefore, the pH of a formulation is a measure of the acidity or alkalinity of the formulation. It is important to evaluate the pH of a drug formulation because pH can affect drug solubility, activity, absorption, and stability, as well as patient comfort (Allen, 2011). The pH of a mixture can also affect other physical characteristics such as viscosity, which is typical for polymeric materials or formulations that contain them (Li and Kwak, 2002, Sa et al., 2019). The rate of product hydrolysis may also be dependent on the pH of the product. Consequently, determining the pH of a formulation can help in optimising the formulation, as it may necessitate the addition of excipients to ensure product stability and tolerability after administration.

The bodies of mammals need specific pH environments for biological and chemical reactions such as catalysis to occur. For instance, an enzyme will typically work effectively in a medium with a specific pH. Additionally, pH can affect the functions of the immune, digestive, circulatory, respiratory, and intestinal systems (Vogel, 2017). Excessive acid in the body is deactivated by buffer systems in the body, which include buffering mechanisms in the blood (chemical buffer) and the respiratory and renal systems (Biga et al., 2020). Blood pH in humans is the consequence of net production, buffering, and excretion of acids and bases in the body. Young people typically have normal kidney function and can therefore maintain their blood pH and bicarbonate levels adequately, such that high acid amounts in the body are sufficiently excreted by the kidneys in urine (Frassetto et al., 2018). However, this ability reduces with increasing age (Frassetto and Sebastian, 1996).

Inadequate performance of the buffer systems results in the use of alkaline minerals from vital organs and bones to help combat acidity. Unfortunately, the latter can result in bone demineralisation. Chronic ingestion of net acid-producing diets combined with reduced kidney function with respect to the regulation of acid-base balance might therefore significantly contribute to osteoporosis (Frassetto et al., 2018, Vogel, 2017).

Typically, the pH of an herbal preparation may not majorly impact human health if it within narrow limits (Beasley et al., 2015). Herbal medicines are generally considered as safe products, and they may be consumed in large quantities and over long periods. As a result, their pH must be evaluated to ensure that they are safe. Moreover, it is well reported that changes in environmental factors and variations in seasons and spatial locations result in differences in the chemical compositions of herbs (Al-Qahtani et al., 2020, Gololo et al., 2018, Ncube et al., 2011). Therefore, it is important to evaluate the pH of herbal medicines that are even prepared from the same plants but in different seasons.

It has been shown that pH can influence medicine quality because it can control chemical reactions and microbiological activity (Liu et al., 2011, Shitanda and Wanjala, 2006). For instance, it is reported that when an herbal preparation has a low pH due to the presence of acidic substances, bacterial count in that preparation could be low; however, at neutral or higher pH levels bacterial contamination could be high. This suggests that a neutral or alkaline pH favours bacterial contamination in herbal preparations. Specifically, it has been indicated that bacterial growth in medicinal products is optimal within a pH range of 5.0–8.5 (Allen, 2011).

Furthermore, Bayliak et al. (2016) have studied the effects of pH on the in vitro H2O2-scavenging and H2O2-producing activities of plant extracts. The results of the study showed that the prooxidant activity of the extracts increased whereas their antioxidant activity decreased at an alkaline pH of 7.8. This clearly shows that pH can affect the pharmacological activities of herbal formulations.

Currently, there are no strict pH standards for herbal medicines. However, we believe it is important to ensure that herbal medicines are formulated to have specific pH values that are optimum to ensure maximum benefits to the consumer. Moreover, variations in pH can affect drug absorption and cause irritation, discomfort, or pain at the site of administration, especially if the difference in pH between a formulation and that at the site is wide (Kinouchi et al., 1996). In the present study, the pH of each batch of 29 varying herbal formulations, including decoctions, powders, and ointments, produced at the Centre for Plant Medicine Research (Mampong-Akuapem, Ghana) over the last two batch years and sold to the public were determined and analysed. The aim of the study was to analyse the consistency of pH of the formulations over the period and to suggest suitable pH ranges for the various categories of products.