All you need to know about shelf-life and storage of Mestinon

Mestinon: Storage and Shelf-life

Mestinon (pyridostigmine)  is a lifeline for Myasthenia Gravis Warriors such as myself. I rely on it to keep my muscles functioning and take it every 4 hours. Without it, I can feel my eyes drooping and my muscles slowly turning to mush.

When we had a postal strike in South Africa, I ran out of Mestinon. ‘Perhaps in three weeks’ I would receive my medication was their verdict. I had to go from pharmacy to pharmacy trying to source Mestinon at my own cost. After this, I vowed to always have some spare. So on a good day, I would stretch out my doses. I now have about a month’s supply extra.

My concern was: 

What is the shelf life of Mestinon and can I take it if it says it’s expired.

Firstly Storage of Mestinon is essential as to maintain the drug's potency.

-          Keep your tablets in the bottle until it is time to take them.
I pack my medication out weekly in a medication dispenser. This helps me save time and keep track if I have taken the medication or not. This is not recommended as Mestinon is sensitive to light and moisture. Therefore, if you take the tablets out of the bottle they may not keep well.
The Mestinon bottle has dark glass and a special cap (amber glass bottles with either aluminum screw caps or low-density polyethylene caps and desiccant). This helps to keep the medication free of moisture and other contaminants.

-          Keep your tablets away from moisture.
Mestinon tablets are hygroscopic, therefore, absorb and retain moisture. If they absorb moisture discoloration of the tablets will occur. Therefore do not store them in the bathroom.  The desiccant helps absorb moisture, so don't toss it once you open the bottle.

-          Keep the temperature below 25°C
Even though it's tempting to keep some spare in the car, this is not advised as an average car can reach internal temperatures of 40°C.

-          Keep out of reach from children.
As this medication is part of our basic survival pack, keep it out of reach of little fingers and basset hounds. A locked cupboard at least one-and-a-half meters above the ground is a good place to store medicines

 The shelf-life under these conditions is three years. Once the bottle is opened, moisture and other environmental factors are in contact with the product and can significantly reduce shelf-life. So be the pedantic patient and ask for the proper packaging.
I have personally noted that was when dispensed in another bottle, Mestinon felt almost ineffective by the end of the month.

However, expired medications have not necessarily lost their potency. The company can not guarantee the effectiveness of the drug after their expiry date.  Ongoing research shows that drugs stored under optimal conditions can retain 90% of their potency for at least five years after the labeled expiration date.

Therefore, if your Mestinon is sealed in the correct packaging shelf life is three years. If you’re a doomsday prepper an approximate 5 years post expiry date is probable, but the potency cannot be guaranteed.

If you need to dispose of any medication, please take it to your pharmacy for medical disposal.    Keep our environment clean.

4) Lee Cantrell. Stability of Active Ingredients in Long-Expired Prescription Medications. Arch Intern Med. 2012;172(21):1685-1687


  1. Thanks for the information. Many of us have expired medication and it is always a concern if we shoudl use it or not. I do keep my expired medications for at least 6 months after they expire jsut becuas eof events like the postal strike.

    I hope you are doing well


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