dosage form is a tablet. 

Yes there is a dec in content at room temp as well.

Yes that might be a reason Mr ganesh....Can you suggest some solution? 

Dear Anwar,

Thanks for your suggestion.

Appreciate your feedback.

Dear Dr Khan

The method you described , I do not think it is decomposition. It is loss of quantity. It is due to volatile ness of essential oils. Previously we worked on cough drop(candy) containing menthol. We always got remarkable loss of menthol content. You have to find out how much loss after manufacturing and certain period of that and put that much extra quantity to resolve this problem or  make  micro encapsulated granules and then start it.

Most aromatic essential oils are volatile, and also degrade faster by heat.  It is their nature.  One possible solution is to use capsule instead of tablet, with the sealed capsule of a nature that will not decompose from the volatile oil.  If must be a tablet, use the foil pouch as suggested by Prof Hussain.

thanks all

If you're problem is mostly from evaporation after manufacture, then encapsulation is your catch-word. There are several methods of encapsulation in discussion at the moment. I don't know what your Tablets are being used for, but if they are meant for swallowing, then I suggest encapsulation with beta-cyclodextrin. This is already an accepted feed additive. The mono- or sesquiterpenes are trapped in sugar cages and are slower to release. I don't know what this does to the taste, it may disguise the taste or flavour, so if you're tablets are meant to be tasted then you'll have to assess the affect on this. Another encapsulation method is to make liposomes, but I think they will not survive the drying out process. 

However, if you are also losing a vast amount of oil to evaporation during the manufacturing process itself, due to heated ingredients, then the challenge relates more to the logistics of preparing your tablets without that initial loss. 

Many essential oils are volatile even at room temperatures. Thermal degradation and loss of low boiling components in known in several essential oils. You may contact Essential Oil Association of India with a large number of manufacturers for sharing their practical experiences.

i am completely agree with Ajay Padmawar .

you may use soft gelatin capsule for this oil