Timing Your Medications for Lab Work
Accurate lab results depend on when you take your medications relative to your blood draw. These guidelines apply to all medications and supplements unless your provider gives you different instructions.
The 6-Hour Rule
Take every medication and supplement at least 6 hours before your blood draw. If your usual dosing time falls within 6 hours of your draw, set an alarm and take that dose early.
Fasting Labs
If your labs require fasting, have nothing to eat or drink except water for at least 10 hours before your draw.
Hydration
Hydrate well starting the day before your draw; it makes your draw easier and your results more accurate. No caffeine of any kind (coffee, tea, energy drinks, or soda) for at least 8 hours before your draw; 12 hours is optimal.
The Night Before
Take all evening medications and supplements at your normal times. Exception: evening-only thyroid or troche dosing with an afternoon draw. See Afternoon Blood Draw.
Morning Blood Draw
Set an alarm and take your morning medications and supplements at least 6 hours before your draw.
Afternoon Blood Draw
- Take your morning doses at least 6 hours before your draw.
- Thyroid or troche, morning and evening dosing: take the morning dose at least 6 hours before your draw. Don’t take the evening dose until after your draw.
- Thyroid or troche, evening dosing only: instead of taking your dose the night before, take it the morning of your draw, at least 6 hours before.
Hormone Creams
Apply your cream as normal, to one arm only, and have blood drawn from the opposite arm.
Injectable Medications
Get blood drawn in the middle of your injection cycle. If you inject twice weekly, get blood drawn the day of your injection, but before the actual injection.
Menstrual Cycle Timing for Hormone Testing
Only if progesterone, estradiol, or FSH are being testedIf your cycle is irregular, get blood drawn any time you are not bleeding.