Taste, colours and flavours from plants come from a great number of active and very complex chemical and biological constituents.
These constituents influence our organism, health and well being.
They can do good - and they can poison.
Any plant - whether you use it for culinary, medicinal or cosmetic purposes - can cause unpleasant reactions in some people.
Even everyday kitchen herbs like rosemary and thyme contain essential oils, which are very poisonous in great amounts.
Also - one part of a plant usually has different constituents from the other parts.
Light, air, heat, frost, preparation, drying, storage, etc. affect plant constituents.
They may even fluctuate depending on season, weather, soil, time of day, etc.
So, it's quite important to know something about the herbs, spices, fruits, berries, etc. that you use to make flavoured schnapps - or put in your food, juice, tea, drink, etc.
Or use for other purposes.
If you are uncertain you may find the answers in herb dictionaries, floras or local field guides, plant encyclopedias or other professional botanical books.
Look it up under the plants' botanical (scientific) names to be sure you find exactly what you are looking for.