Hello, This is Dr. Dodson and I just happened to run across your question while I was looking for something else.
The answer is that Vyvanse is stable in water essentially forever and without refrigeration. The FDA says you can dissolve Vyvanse in water for people who cannot swallow pills but that you should throw away whatever is left. This is because the FDA did not specifically study whether Vyvanse remained stable or not.
But the DEA (Drug Enforcement Administration) did study it because they were worried Vyvanse could be put in water and injected (it is their job to worry about such things.) They put Vyvanse in a Mason jar of tap water and put it on a bookshelf for one year. At the end of that year there was no degradation of the lis-dextroamphetamine prodrug delivery system. It was as good as the day it was put in the water. My patients have consistently reported the same thing to me. For example, a student will usually buy the largest 70 mg size and do the math to make up a pitcher of Vyvanse in water at the first of the semester.
This feature can save a lot of money for people who take relatively low dosages (ex. A person who takes a dose of 20 mg can get 3 1/2 doses out of a single 70 mg capsules (all of the various dosage strengths cost the same).
One minor caveat… there will be a white powder that falls to the bottom of the container. It is not medication. It is titanium dioxide that is put in the capsule to prevent caking. It is totally inert. I am told by my patients that if you stir it up, it makes your teeth feel gritty for a few minutes.
I hope this is helpful,
Bill Dodson, M.D.