Wasn't exposed to light. Still hasn't been opened. The expiration date is 3+ years away.
This was an expensive little 30ml bottle at $179 from b12site. Is it now completely useless because it was delivered at such a high temp by the P.O.? (It is definitely over 86 degrees.)
Until I receive a reply, I'm putting it in a dark, cool place before opening.
Please explain, if you know, what happens when the meth-c gets over 86 degrees (F).
I believe I failed to mention this is for injections, though it's probably obvious in context.
It is UV light that deteriorates B12, not heat.
cobalamins do have heat sensitivities as well as light sensitivities - I'm not sure what the reactive path is for methyl but it will probably convert to hydroxo - the longer it was exposed the more would have been converted. Methyl is more heat sensitive than hydroxo and cyano. It will still be B12 but not necessarily methyl - so no problems with using it but if you find that you aren't responding as normal when you do that might be the reason.
Ah! I think you got that methyl -> hydroxo from me. I was wrong. PAS-Admin corrected me by saying that it gets converted to aquocobalamin (with an H2O, not OH, replacing the CH3). I can't remember but I think it is probably, mainly, inactive.
I thought that was a bio-chemistry process in the cells - so needed another chemical to mediate but ... too much biochemistry and my brain starts to overheat 
Here's the thread where I learned of my error - healthunlocked.com/pasoc/po...
tl:dr
It seems that aquacobalamin combines with glutathione to irreversibly form glutathionylcobalamin. The paper that you quote in that thread, and one quoted by PAS-Admin, suggest that glutathionylcobalamin is an intermediate in the biochemical synthesis of the two active forms of B12. But the two later papers use that word 'irreversibly', which suggests it is not.
However, I've figured out how to make my fortune. I shall buy loads of out-of-date methylcobalamin, dissolve it in water and leave it to go off in the light for a few weeks. Then I'll add some glutathione and market it as glutathionylcobalamin - the magic combination of methylcobalamin (the best type - until now) and glutathione (the wonder antioxidant).
Quote the two old papers, set up a clickbait website, write a book and wait for the hype to spread.
Can't fail.
I've been taking B12 several years now for pernicious anemia (I had gastric bypass in 1999). In 2008 I went from barely able to walk a mile to running a half marathon (+ half triathlons) over 11 months once I was diagnosed & treated with cyan in the first couple months of that.
But in recent years as I'm now over 50 & finishing up menopause my energy level has really dropped just taking the monthly cyan.
Here on this forum a few days ago is where I first learned there was a natural alternative to cyan. I'd never heard of meth...
My plan is to reboot by taking cyan daily for a month, but using the meth one day/week. I'll ween to one shot overall per week the next month, then back to just monthly.
Bottom line - let's hope the extreme heat in the mailbox didn't do damage & that I see major improvement over the next couple months.
Thanks. Frustrating. I may have just spent all that money for nothing, & now I have to wait a couple months of using it to find out if it's ineffective. All because I live in Florida & have to share my mail box with the rest of the neighborhood!
Did the pharmacy whence it came detail that it needed to be shipped cold? If not, then I reckon they're to blame and the PO is innocent.
In the UK we have seen a huge rise in special packaging for things like salmon being delivered by post. If heat is an issue (and I think it might be), then the sender is responsible. They could have used a "keep cool" packaging - perhaps something like this company produces:
Good point. There's no stipulation about packaging at B12site.com, but since my options are limited without health insurance/prescription, I will be sure to request refrigerated packaging next time I order.
I must say, B12site was very quick, & shipping was free. I had it in 2 days. And the expiration is 12/29/19. I would definitely be OK paying a little extra for special packaging to ensure the whole thing doesn't get wasted.
Just some general info on why temperature can be important. For most chemical reactions that don't use a catalyst (so not the majority of biological reactions) the rate of the reaction roughly doubles with every 10ºC rise in temperature.
So, if the rate of degradation of a chemical is such that half of it is degraded after 1 year at 0ºC, then you can expect that half of it would degrade after about 10 days at 50ºC and 6 weeks at 30ºC (86ºF).
But we don't know how quickly methylcobalamin degrades at any temperature. Most places that supply B12 for injection in the US (that I've found) seem to give it a 1 year use-by date and say that it should be stored refrigerated. So I think it would be a good guess to say that 1 year at 10ºC would be about the same as three months at 30ºC.
Which means that I doubt that a few days at 30ºC would make a huge difference.
fingers crossed!
Oxford Biosciences Methylcobalamin
Accessing Methylcobalamin ampoules UK 
How to store Methylcobalamin
Oxford Biosciences methylcobalamin in 2023 ( - 6yrs on!).
cobalamin v methylcobalamin sublinguals
