Dosage and Herbal Remedies

They are right, BUT only to a limited extent.

Today most commercial herbal preparations that are sold over the counter have been prepared to rigorous standards. They may not be controlled by organizations like the FDA and therefore may not be subjected to the clinical trials that pharmaceuticals are subjected to but then most do not need to go through these trials as they are not new. Herbal remedies with few exceptions, have been tried and tested over hundreds of years.

These commercial herbal preparations are measured and dosage and contraindications is included.

Dosage becomes an issue when herbal remedies are prepared in the traditional manner.

For instance the strength of an infusion depends on many factors:

The herb:
Where was it grown? This may not be an issue with many herbs but in some of the cases the climate and soil that the herb grew in has a dramatic influence on the content of the desired and undesired constituents.

Which herb? An infusion made from Green Tea is likely to render its beneficial qualities regardless of whether it is weak or strong (in fact we have developed individual tastes for how strong we like our tea). An infusion made from Belladonna is likely to kill long before your sense of taste will tell you that it is too strong.
There are some herbs, like Belladonna, Aconite and Ignatius beans that MUST be left to qualified, knowledgeable professional to prepare but there are many more herbs where dosage is not an issue.

Knowledge:
Touched on above, but are you using the right herb? Comfrey is a very valuable medicinal herb when used as a topical application but should never be ingested. Not all herbs can be used as an infusion. Not all herbs have value as a poultice. 

Harvesting:
Some herbs have to be harvested at just the right time to ensure that the desired constituent is at its highest level (or even present at all). Get this wrong and your herbal medicine will have less or no efficacy.

Part used:
The whole herb is not always useable. In some cases it is the seed that contains the medicinal ingredient, in others the leaves or bark or even just the bark of the roots.

Preparation:
In an infusion alone the method of preparation can vary the dose of medicinally active compounds dramatically. If the amount of the dried herb used varies, if the amount of boiling water changes, if the temperature of the water varies, if the water cools faster or slower it will all affect how much of the active compounds end up in the water. Changing all of the above and there will be no way of determining the potential difference in dosage.

Adulteration:
Some herbs can easily be mixed with other substances which are not easily detected. In many of the countries where herbs are grown quality control is poor and individual growers are paid by weight or volume. Adding other, easier to obtain, plant material is a common way of cheating the system.
These adulterations can reduce the quality and ration of active substances.

The dosage issue can be totally avoided by buying standard extracts. Virtually all of the manufacturers of standard extracts have devised a way of controlling the strength of their extracts and they also always provide dosage instructions. For those of you that wish to make your own remedies always remember to start by under dosing (making the remedy weaker) and observing any potential side effects before increasing the dosage. Because bulk herbs can vary by batch, any new supply of herb should be tested in the same way. Never assume that two batches are the same.