Supplements: quality, contamination and heavy metals
Supplements may contain lead, nickel and arsenic. What this means for your animal and when to see a vet immediately.
Short & honest
Plant-based supplements sometimes contain measurable amounts of heavy metals (lead, nickel, arsenic) — evidence grade B. Contamination has been demonstrated in market studies; risk to animals is real but insufficiently investigated on a species-specific basis.
Safety assessment: Risky
Veterinary review not yet completed
This page is awaiting review by a registered veterinary surgeon. Until then, treat the text as education based on the sources listed — not as a verified veterinary judgement.
Why quality control of supplements is crucial
Supplements for animals — herbs, adaptogens, algal meals, mineral mixtures — do not fall under the strict registration requirement for veterinary medicinal products in the Netherlands. The producer is responsible for safety themselves; external quality control is limited. Market research shows that this brings real risks.
Research into herbal supplements on the Polish market showed that a majority of the tested adaptogenic products exceeded safety limits for lead or nickel [1]. UAE market research on 277 supplements detected lead, cadmium and arsenic using sensitive ICP-MS analysis [2]. Both studies focused on human consumers, but the metals found are at least as relevant for animals — and more dangerous for many animal species.
Heavy metals: the primary risks
Lead (Pb)
Lead accumulates in bones and soft tissues. Chronic exposure via a supplement can remain unnoticed for weeks to months before symptoms occur. Young animals, small mammals and birds are considerably more sensitive than adult large animals [1].
Nickel (Ni)
Nickel exceeded safety limits by more than 300% in some ashwagandha samples [1]. Little is known about chronic animal toxicity of nickel via supplementation — this is not a reassuring conclusion, but a knowledge gap.
Cadmium (Cd) and arsenic (As)
Cadmium causes damage to kidneys and liver; arsenic disrupts multiple organ systems. Both were demonstrated in supplements on the market [2]. For animals, comparable standardisation is lacking in the context of long-term supplementation.
Species-specific vulnerability
Not all animal species react equally to heavy metals:
| Animal species | Increased risk |
|---|---|
| Cats | Limited metabolism capacity for many toxins |
| Small mammals (rabbit, guinea pig, rat) | High body surface-to-weight ratio; faster relative uptake |
| Birds (parrots, chickens) | Very sensitive to lead; low doses can be fatal |
| Dogs | Sensitive, but less so than cats for some substances |
| Large herbivores (horse, cattle) | Risk with long-term use of contaminated herbal mixtures |
How contamination occurs
Contamination occurs at multiple points in the chain:
- Soil and cultivation area — Plants take up metals from contaminated agricultural land; region of origin also determines the risk [1]
- Processing and excipients — Tablet products sometimes contain more lead than capsules or powders, possibly due to contaminated binders [1]
- Batch variability — One clean analysis result does not guarantee that a subsequent batch is equally clean [1]
"Natural", "organic" or "herb-based" says nothing about the absence of heavy metals.
What you can do
- Only buy supplements from suppliers that make demonstrable, batch-specific analysis reports (Certificate of Analysis, CoA) available, with explicit measurement values for heavy metals
- Check whether the product has been tested with ICP-MS — the most sensitive standard method for detecting low concentrations [2]
- Always inform your veterinary surgeon about every supplement your animal uses, including brand, formulation and duration of use
- Stop the supplement immediately and consult your veterinary surgeon if you suspect symptoms that could match poisoning
No supplement is inherently safe because of its plant-based or natural origin. Quality control by independent analysis is the only factual certainty.
Why this verdict?
Two market studies — a narrative review of 11 adaptogenic supplements on the Polish market [1] and a cross-sectional study of 277 products on the UAE market [2] — demonstrate using validated analytical methods that heavy metals occur in supplements. Grade B because contamination is demonstrable, but the studies are limited in scale, cover only one market, and do not measure bioavailability or species-specific toxicity.
Interactions with medication
- Heavy metals can disrupt the absorption of essential minerals (zinc, iron, calcium) with prolonged use
- Cumulative exposure increases when multiple plant-based supplements are given simultaneously
Legal status (Netherlands)
In the Netherlands, supplements for animals fall under European animal feed legislation (Regulation (EC) 767/2009 and 1831/2003), not under the Wet dieren (Animals Act) as veterinary medicinal products. Maximum limits for heavy metals in animal feed are established in Directive 2002/32/EC. Treatment advice and diagnosis are legally reserved for veterinary surgeons.
Sources
- [1] Heavy Metal Contamination in Adaptogenic Herbal Dietary Supplements: Experimental, Assessment and Regulatory Safety Perspectives. Biology (MDPI) 14(11):1479, 2025. Narrative review source ↗
- [2] Heavy Metal contamination of Dietary Supplements products available in the UAE markets and the associated risk. Scientific Reports 10:19330, 2020. Narrative review doi:10.1038/s41598-020-76000-w