Debate about non-conventional practices usually sorts them by origin or plausibility. A more useful division is by relationship to medical care, because whether something is used alongside treatment or instead of it determines the risk almost entirely.
The two positions carry different risk profiles
A practice used alongside conventional care adds to it. If it does nothing beyond providing pleasant attention, the loss is the money and the time.
A practice used in place of conventional care removes something. The cost is whatever the displaced treatment would have provided, which for treatable serious illness can be substantial.
Most documented harm in this area follows the second pattern rather than arising from the practices themselves being dangerous.
Symptom relief and disease modification are different targets
Many complementary approaches are aimed at how someone feels — pain, nausea, tension, distress — rather than at the disease process.
Improving how a person copes during treatment is a legitimate goal and is increasingly provided within cancer and palliative services for that reason.
The problem arises when relief of a symptom is taken as evidence that the underlying condition is being addressed, which does not follow.
Interaction is a real and underreported risk
Herbal preparations and high-dose supplements contain pharmacologically active compounds and can alter how prescribed drugs are metabolised.
Some affect blood clotting, some alter the clearance of other medicines, and some are relevant to anaesthesia, which is why surgical teams ask about them.
Patients frequently do not mention these products because they are not thought of as medicines, so the interaction is discovered only when something goes wrong.
The regulatory gap is about manufacture as much as claims
In many jurisdictions these products are regulated as foods or supplements rather than medicines, so pre-market evidence of effect is not required.
Manufacturing oversight is correspondingly lighter, and independent testing has repeatedly found products whose contents differ from their labels.
Arrangements vary considerably between countries and change over time, so what a given certification actually guarantees is worth checking rather than assuming.
The questions worth asking a practitioner
What is this expected to change, how would we know if it were not working, and how long before that judgement is made.
A practitioner who welcomes those questions and who wants to know what else you are receiving is operating in the complementary position.
One who discourages contact with medical services, advises stopping prescribed treatment, or treats questions as a lack of faith is operating in the substitutive one.