Most countries have the equivalent of the FDA in the US, which regulates medicine and supplements to a certain degree. In 1994 the Dietary Supplement Health and Education Act(DSHEA) was passed, under which dietary supplements fall under. Of course having multiple industries and large amounts of money involved is not conducive to the best outcome for the consumer, but that is the reality. In colloquial and tribal terms, Big Pharma and Big Supplement got their territories carved out.
The main difference between drugs and supplements is that, for drugs, pharmaceutical companies are required to scientifically prove efficacy and safety, and claims can be made for the specific use approved. For supplements, unless it is a New Dietary Ingredient (NDI), manufacturers are practically free to do whatever they wish. Technically there are recent requirements to adhere to cGMP (2007, to ensure production quality), however in reality there is widespread non-compliance. It is up to the FDA to prove that a supplement is unsafe, and so far it has only done so on one occasion with ephedra, and nowadays does little more than posting warnings on its website and hoping people read them. Regardless of whom is to blame for the apparent lack of resources in the FDA, the fact remains that this part remains mostly unregulated.
One of the rationales behind supplements was that supplements were presumed to be safe because of long history of use. The huge cost of double blind, randomized controlled studies are prohibitively expensive and time consuming, and seemed like overkill for innocuous supplements. However, in reality, naturalistic fallacy aside, most supplements are far removed from their original states, with the active ingredient extracted and concentrated beyond what could have been reasonably consumed traditionally – much farther along the dose-response curve than its original form. In other words, an unregulated drug. There is no requirement for efficacy or safety studies. The reason you rarely if ever see a “Contraindications” section for supplements is not because it does not exist, but because it is not required and often unknown.
Of course, many of the supplements, especially traditionally known vitamins and minerals, have been well studied scientifically and the pharmacodynamic and pharmacokinetic properties are well known. Others have evidence ranging from peer-reviewed studies to fake anecdotes. This graph beautifully shows some of the supplements, uses and current significant studies or lack thereof; the ranking is somewhat subjective but useful as reference.
My viewpoint is practical and some would say pessimistic or depressing. I believe that regardless of multiple negative scientific findings, short of outlawing a product, actual behavior will not be significantly changed, due to confirmation bias, cognitive dissonance, distrust or just plain stubbornness. It only takes one small scale, poor quality preliminary study with bad methodology, cherry picked data with dubious funding and strong researcher bias to be touted as the next miracle drug, I mean supplement. The fact that journals rarely publish replication studies, especially when it contradicts prior claims, does not help instill trust either. It is a sad but true reality.