How long does it take for a B12 shot to wear off?
That’s a tricky question, because it depends on what you’re trying to ask exactly. Is it how long the energy from a B12 shot lasts (as well as the other benefits of B12 shots), or how long any B12 injection side effects last? In any case, we’ll touch on both points.
How Long Does a B12 Injection Last?
First, a little primer on B12:
B12 is water-soluble, so any excess is urinated out. This is why it’s impossible to overdose. In cases of cyanide toxicity (think of a person saved from a fire after inhaling a lot of smoke), 5,000,000µg of B12 is injected as treatment to clear the cyanide out of the body. Sometimes, treatment is repeated for a total of 10,000,000µg of B12. That’s more than 4 million times the recommended daily dose, and still you can’t overdose. B12 levels in the blood return to normal once all that excess has been urinated.
And so, this brings back our question:
How long does a B12 shot last and stay in your system?
Often, most of the B12 from a shot is flushed out in the urine within hours. Only a tiny bit is absorbed. For this reason, we recommend to inject daily, especially in the presence of neurological symptoms. In cases like these, you just can’t rely on once-a-week or once-a-month shots, which are unfortunately the doses doctors most often prescribe.
Also, this is crucial:
For the full effects of B12 to take place, inject daily for at least three months. One injection will barely do anything. Your red blood cells have a lifespan of 90 days. Every day, some cells expire and new ones replace them. When you inject daily, you’re making sure that three months from now all of your malformed red blood cells will have been replaced by healthy ones. Only then will you feel like a completely new person.
But How Long Do Reactions Last?
B12 isn’t like coffee, you most probably won’t notice any reaction to it. When adverse reactions do occur, they’re often the result of a problematic substance in the product, for example carboxymethyl cellulose, mannitol, or benzyl alcohol. So if any preservative was added to the solution, it may very well be the cause of any side effect. Here’s an example case of adverse reactions to vitamin B12 shots due to benzyl alcohol sensitivity.
How long will these reactions last?
It’s hard to say, because there’s a variety of substances that could cause such side effects to B12 injections. Your best insurance to protect yourself against such cases is to only accept injecting pure B12, mixed only with pure, preservative-free, sterile saline.
Best of luck.