Adulterants and contaminants in herbal supplements sold in Accra (Ghana), for improved sexual performance and their associated health risks

Felicia Akuamoa

Research output: Thesisinternal PhD, WU


The use of herbal supplements for sexual improvement and recreational purposes is a rather common practice in Ghana. Although the high accessibility, acceptability and assumed benefits of herbal products has promoted growth in the herbal industry, the presence of adulterants and other contaminants in these products is a major health concern.

In this thesis, selected herbal supplements were initially screened using the PDE-Glo bioassay to determine their inhibition potentials against PDE-5 enzyme activity, the mode of action underlying their effect on erectile function. Results based on the bioassay revealed that about 90% of the samples were able to inhibit PDE-5 enzyme activity at various degrees, with estimated intakes of 25 samples (62.5%) pointing at daily doses higher than 25 mg sildenafil equivalents and 9 (22.5%) of these even at doses higher than the maximum recommended daily intake of 100 mg sildenafil equivalents. Further investigations were carried out to confirm if the observed effects were due to inherent plant constituents or merely the result of added synthetic PDE-5 enzyme inhibitors.

Further chemical analysis revealed significant amounts of sildenafil and other approved PDE-5i in 13 out of the 40 supplements. Based on data from the chemical analysis, the estimated daily intakes (EDIs) of six out of the 13 even resulted in EDIs above 100 mg sildenafil equivalents. Only one sample contained a natural ingredient (icariin) potentially able to inhibit PDE-5 enzyme activity, but its concentration (0.013 mg/g) was too low to explain the observed response in the bioassay. The estimated concentrations of PDE5 inhibitors in 35 supplements as derived from the bioassay results, were in line with those of the LC-MS/MS analysis, while discrepancies were observed for 5 supplements. A tiered approach for one of the latter supplements using the PDE-Glo bioassay to select the positive fraction and further examination with LC-MS/MS and 1H-NMR revealed the presence of hydroxythiohomosildenafil, a sildenafil analogue not yet included in the LC-MS reference library. These results highlight the importance of the bioassay to detect unknown PDE-5 inhibitors.

To further investigate the safety of the herbal supplements, the presence of contaminants such as polycyclic aromatic hydrocarbons (PAHs), dioxins (polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs)) and dl-PCBs possibly introduced into the products as a result of contaminated raw materials or during processing were also investigated. Selected supplements were initially screened using the DR CALUX® bioassay in order to identify the presence of stable (acid-silica clean-up and 48 hrs exposure) and less stable (without acid-silica clean-up and 4 hrs exposure) aryl hydrocarbon receptor (AhR)-agonists. The results revealed that the selected supplements contained only low levels of stable AhR-agonists like dioxins and dl-PCBs, while some contained less stable AhR-agonists like PAHs.

Ten supplements selected for confirmation with GC-HRMS analysis contained PCDD/Fs and dl-PCBs at levels varying from 0.01 to 0.19 pg toxic equivalents (TEQ)/g, while the level of the sum of 4 polycyclic aromatic hydrocarbons (Σ4PAHs), representing less stable AhR agonists, ranged from not detected (ND) to 25.5 ng/g. These concentrations were in line with the responses observed in the DR CALUX® bioassay. The concentration of PCDD/Fs and dl-PCBs corresponded to EDIs ranging from 0.001 to 0.12 pg TEQ/kg bw/week for a 70 kg bw consumer, which is below the established tolerable weekly intake (TWI) of 2 pg TEQ/kg bw/week, thus indicating low concern for consumers’ health. Similarly, the EDIs based on the detected Σ4PAHs in supplements ranged from 7.2 to 111 ng/day, or 0.1 to 1.6 ng/kg bw/day, which compared to carcinogenic effects in animals corresponds to margin of exposure (MOE) values above 10,000, indicating a low health concern.

Finally, the presence of pyrrolizidine alkaloids (PAs) in the 40 supplements as a result of contaminated raw materials and/or the unintentional co-harvesting of raw materials with PA containing weeds, was examined using liquid chromatography mass spectrometry (LC/MS). Up to 17 different PAs were identified in 19 out of the 40 samples. In decreasing order, the most detected PAs were rinderine (in 15 samples), its N-oxide (10), intermedine (11), its N-oxide (11), lycopsamine (8) and its N-oxide (5). The total sum of PAs in samples ranged from 0.005 to 3.2 µg/g, resulting in EDIs from 0.01 to 12 µg/day, corresponding to exposures from 0.0002 to 0.2 µg/kg bw/day for a 70 kilogram bodyweight person. When compared to a BMDL10 of 237 µg/kg bw/day for liver tumours in rats treated with riddelliine, the margin of exposure (MOE) values ranged from 1200 to 1,400,000 with 8 samples showing MOE values below 10,000, thus indicating a health concern upon long-term regular use of these 8 supplements.

The presence of contaminants and especially added adulterants in the selected supplements compromises their purity and safety, the latter depending on the concentrations present. These findings are indicative of what is pertaining to the numerous herbal products available on the Ghanaian market. The practical approaches employed in this thesis, using a combination of a bioassay and chemical analysis to determine the presence and concentrations of added pharmaceuticals and undesirable contaminants is expected to be applicable in most laboratories. These approaches can be applied in investigating other herbal products available on the Ghanaian market.

The adulteration of herbal products with active pharmaceutical ingredients and the presence of contaminants continues to be a problem for regulatory agencies globally including Ghana. In the present thesis, the presence of intentionally added adulterants in the selected herbal products shed a light on on-going practices in Ghana and provides some answers to the numerous reported casualties and deaths of consumers of sexual enhancing herbal products sold on the Ghanaian markets.


Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
  • Rietjens, Ivonne, Promotor
  • Hoogenboom, Ron, Co-promotor
  • Bovee, Toine, Co-promotor
Award date9 Feb 2022
Place of PublicationWageningen
Print ISBNs9789464470208
Publication statusPublished - 2022


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