There is no such thing as clinical grade, CPTG (certified pure therapeutic grade), food grade, or anything else you may have heard. Pure unadulterated essential oils will be therapeutic whether they have been grown for the food industry or not.
These terms are created by the companies to help them sell more products, they want to make their essential oils stand out among someone else’s so you purchase from them. All of the purity and grade claims are just marketing techniques. There is no legislation around selling essential oils in the UK as they fall into the general category of legislation which is so broad and contains so many things there is very little policing within it.
When buying an essential oil ensure the label has on the botanical name which is often referred to as it's Latin name, country or origin, a use by or best before date and a company's name or address.
There will be variety in the same oils from different suppliers not because of purity or grade but because of environmental factors. Essential oils come from plants and how high they are grown above sea level, the amount or sunlight and rain and what country they are grown in will make a difference in chemistry and therefore in the scent.
To know whether an oil is of good quality is by asking the supplier for a GC-MS document which is something that analyses each batch of essential oil. Gas-Liquid Chromatography, commonly referred to as gas chromatography (GC), determines the components and their relative proportions in a given essential oil. Any good supplier should have these for each batch of essential oil as it shows they are checking the quality of what they are selling and a GC trace is an industry standard test. Certificates of Analysis are also something that companies do so ask for this if you are still not sure.
In summary the therapeutic or pure grade claims from companies can’t be the reason you purchase; these are an internal grade within that company and not a standardised grade across the industry. It is also why companies cannot be compared according to this claim. You need to do other research before making your decision.
Any good quality essential oil provider will be more than happy to answer your questions and help with any queries. Currently there is very little legislation surrounding selling or labelling essential oils in the UK so we recommend checking the Aromatherapy Trade Councils website for a list of suppliers as these have all been checked and approved by a regulatory body. The link for this is https://www.a-t-c.org.uk/membership-list/ and whilst it is not an exhausted list it is comprehensive enough to include suppliers for all your needs.