According to Health Canada, a recent study reported in JAMA showed that many Ayurvedic medicines contain high levels of lead, mercury and/or arsenic. One product was:
found to contain arsenic levels in excess of 40 times the maximum allowable concentration for drugs. Described by its labelling as a blood purifier used for skin diseases and as a treatment for digestive problems, SAFI is available as a liquid in a 200ml bottle and packaged in a lime green box, bearing a black and red label on both the front and back. Consumers are advised not to use this product.
Good advice. Of course, even many evidence based medicines can have bad effects, some unexpected. For example, critics will quote recent studies of Vioxx and similar drugs as evidence that western medicines can also be harmful. There is some truth in this. But western medicines, because they are evidence-based, are usually beneficial too, and so there is a risk / reward trade-off to be made.
With many alternatives such as Ayurvedic, there is no evidence that the treatment does any good, (and often evidence that it does no good), and so the risk has no balancing reward at all. Instead they offer:
a false hope based on an unscientific imagination seeped in mysticism and cheerily dispensed gibberish. Science is unnecessary to test Ayurvedic claims since "the masters of Ayurvedic medicine can determine an herb's medicinal qualities by simply looking at it
CBC News illustrates a basic problem:
Practitioners and followers believe the heavy metals in the products carry therapeutic value.
Western scientists say heavy metals pose a health risk because they accumulate in vital organs.
Alternatives, unlike real medicines, do not need to be tested for safety (or efficacy), and can be marketed in the US as long as it cannot be proved they are harmful. The problem with this should be obvious. Proponents of alternatives often promote the benign nature of their therapies as opposed to the supposed dangers of therapies that actually have been shown to work. Clearly they are often as wrong in this assertion as they are in their claims for the efficacy of their products.