How far apart should you take vitamin B12 from levothyroxine?
There’s usually no need for a long waiting period between levothyroxine (for thyroid hormone replacement) and vitamin B12. In most cases, you can take them at the same time or with no special spacing.
The main reason people ask about timing is levothyroxine’s sensitivity to absorption from certain substances; vitamin B12 generally does not block levothyroxine absorption in the way that iron, calcium, magnesium, or some antacids do.
When spacing does matter: focus on what can interfere with levothyroxine
Even though B12 usually isn’t a problem, levothyroxine is commonly separated from these agents to protect absorption:
- Calcium supplements
- Iron supplements
- Magnesium (including some supplements)
- Aluminum-containing antacids
- Some cholesterol binders (e.g., cholestyramine/colestipol)
- Sucralfate
If your B12 is taken alongside any of those interfering products, that’s when spacing becomes important.
Practical timing approach (simple schedule)
If you want a cautious, easy routine:
- Take levothyroxine on an empty stomach (as prescribed).
- Take vitamin B12 at the same time as long as it’s not combined with an interfering product.
- If you prefer separation for convenience, taking B12 later in the day is fine too (for example, with breakfast or lunch), as long as levothyroxine timing rules are followed for the things that interfere.
What to do if your B12 is part of a multi-vitamin or “B-complex”
Check the label. Some multivitamins include calcium, iron, or magnesium. If your B12 product contains any of those, then you should space it away from levothyroxine rather than relying on a B12-only rule.
Tell me what you’re taking and I’ll help you time it
If you share:
1) the brand/dose of levothyroxine,
2) the form of B12 (tablet, sublingual, injection), and
3) whether your B12 is in a multivitamin/B-complex,
I can suggest a specific schedule that avoids the common levothyroxine absorption issues.