Natural Health Products

Canadian Diabetes Association Clinical Practice Guidelines Expert Committee

Richard Nahas MD, CCFP Jeannette Goguen MD, MEd, FRCPC

  • Key Messages
  • Recommendations
  • Figures
  • Full Text
  • References

Key Messages

  • Seventy-eight percent of patients with diabetes reported taking a natural health product (NHP) for various indications.
  • Some NHPs have shown a lowering of A1C by ≥0.5% in trials lasting ≥3 months in adults with type 2 diabetes, but most are single small trials so it would be premature to recommend their widespread use.
  • Healthcare providers should always ask about the use of NHPs since some may result in side effects or drug interactions.


Natural Health Products (NHPs) include herbal medicines, vitamins, minerals and other essential nutrients, probiotics and many other naturally occurring substances. Since 2004, they have been regulated in Canada by the Natural Health Products Directorate of Health Canada.


These guidelines include NHPs because they are widely used by patients, but the evidence of their efficacy and safety is unknown to most prescribing physicians. In a recent Canadian study of 502 patients with diabetes, 78% reported taking an NHP, with similar frequency in people with type 1 and type 2 diabetes (1). While it is important to be aware of potential harms, side effects and drug interactions, some NHPs may be potentially important new therapeutic agents. Interestingly, metformin is derived from French lilac, a remedy used to treat diabetes since the Middle Ages, and identification of the active agent guanidine led to the synthesis of biguanides (2).

In general, the current level of evidence for the efficacy and safety of NHPs in people with type 2 diabetes is lower than that for pharmaceutical drug treatments. Trials tend to be of shorter duration and involve smaller sample sizes. At the present time, concerns remain about standardization and purity of available compounds, including their contamination with regular medications and, in some cases, toxic substances (3).

While a number of NHPs have been studied to evaluate their impact on cardiovascular and other outcomes in patients with type 2 diabetes, this guideline is limited to NHPs for improving glycemic control. Trials were considered for review if they were randomized, controlled, and reported changes in glycated hemoglobin (A1C) over at least 12 weeks of treatment. Positive trials were those that demonstrated a reduction in the placebo-subtracted A1C of at least 0.5%.

The following NHPs lowered A1C by ≥0.5% in trials lasting at least 3 months in adults with type 2 diabetes:

  • Coccinia cordifolia (4)
  • Ganoderma lucidum (5)
  • Salacia reticulata (6)
  • Soybean-derived pinitol extract (7)
  • Touchi soybean extract (8)
  • Pterocarpus marsulium (vijayasar) (9)
  • Gynostemma pentaphyllum (10)
  • Marine collagen peptides (11)
  • Silymarin (12,13)
  • Citrullus colocynthis (14)
  • Trigonellafoenum-graecum (fenugreek) (15)

These products are promising and merit consideration and further research, but, as they are mostly single, small trials, it is premature to recommend their widespread use.

The following NHPs failed to lower A1C by ≥0.5% in trials lasting at least 3 months in adults with type 2 diabetes:

  • Tinospora crispa (16)
  • French maritime pine bark (17)
  • Soy phytoestrogens (18)
  • Agaricus blazei (19)
  • Antioxidants (fruit/vegetable extract) (20) , (pomegranate extract) (21)
  • Camellia sinensis (22)
  • Cinnamomum spp (cinnamon) (23–27)
  • Momordica charantia (bitter melon or bitter gourd) (28)
  • Flaxseed oil (29)
  • Ginseng (30)
  • Coenzyme Q10 (31)
  • Vitamin C (32)
  • Vitamin D (33–35)
  • Vitamin E (36–38)

It should be noted that, in many cases, small sample sizes made the trials insufficiently powered to establish a significant benefit from NHP interventions.

The following NHPs have demonstrated conflicting effects on A1C in trials lasting at least 3 months in adults with type 2 diabetes:

It should be noted that vanadium, a trace element that is commonly used to treat type 2 diabetes, has not been studied in trials evaluating glycemic control over a period of 3 months or longer.


It is important to consider potential harm from the use of NHPs. In 1 trial of Tinospora crispa , hepatotoxicity was seen in 2 patients (16). Large doses of Citrullus colocynthis can induce diarrhea, but no side effects were reported in the lower doses used in 1 trial (14). Momordica charantia , an NHP commonly used for glycemic control, is an abortifacient (62). Most clinical trials have evaluated small sample sizes over relatively short periods of time and, thus, may not identify side effects or risks.

Drug-herb interactions may also occur. The most well described is Hypericum perforatum (St. John's wort), which can affect the metabolism of many drugs, including statins, by inducing CYP3A4. Some studies have reported poorer glycemic control in patients using glucosamine sulfate for osteoarthritis, but a systematic review concluded that the evidence does not support this concern (63).

Clinicians should ask all patients with diabetes about their use of NHPs. Potential concerns should be addressed using a patient-centred approach that ensures patient safety while respecting their views to maintain a positive therapeutic relationship. For more detailed information about specific NHPs, practitioners should consult previously published reviews (64).


  1. 1.Natural health products are not recommended for glycemic control for individuals with diabetes as there is insufficient evidence, at this time, regarding efficacy and safety [Grade D, Consensus].
  2. 2.Healthcare providers should ask about the use of natural health products [Grade D, Consensus].


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