Wrong containers
Don't use anything but a glass container.
Nitroglycerin is a very unstable substance and will be damaged by moisture, warmth, light, and coming in contact with just about anything other than glass. You need to keep your tablets in a dark, dry, cool (in your pocket or on a necklace next to your skin is no good) container.
Plastic, 
aluminum or any substance other than glass will ruin the effectiveness of the nitroglycerin tablets. That's also why cotton padding is not used in nitroglycerin containers.
On this page we will show you pictures of containers we have found being sold for use as nitroglycerin containers. Just because they are sold in a drug store or because some on the internet says they are for nitroglycerin, don't be fooled.
Many of the sellers don't know the difference