Short answer: At least 30 minutes, and the label asks for that wait before any food, drink or other medicine too. The Fosamax (alendronate) label says calcium supplements, antacids and other oral medicines with minerals like calcium or magnesium interfere with absorption, so patients should wait at least half an hour after Fosamax before taking any other oral medicine. The NIH magnesium fact sheet suggests keeping magnesium products at least 2 hours apart.
The label tells patients to take Fosamax first thing after getting up, at least half an hour before the first food, drink or medicine of the day, with plain water only. It says calcium, antacids or oral medicines containing multivalent cations (minerals such as calcium, magnesium and iron) will interfere with absorption, so patients should wait at least half an hour after Fosamax before taking any other oral medicine.
It also says other drinks, including mineral water, and food are likely to lower absorption, and that waiting less than 30 minutes, or taking Fosamax with food, drinks other than plain water, or other medicines, will lessen its effect. The patient information names mineral water, coffee, tea, soda and juice as drinks not to take it with.
The label says the full glass of water and staying upright help the tablet reach the stomach and lower the chance of irritating the esophagus. The usual osteoporosis treatment dose is 70 mg once a week or 10 mg once a day.
The timing rule is not a reason to drop calcium. The label tells prescribers to have patients take supplemental calcium if their diet does not provide enough, says some people may need vitamin D, and says low blood calcium must be corrected before starting Fosamax.
The NIH Office of Dietary Supplements magnesium fact sheet says magnesium-rich supplements or medicines can lower absorption of oral bisphosphonates such as alendronate and suggests taking them at least 2 hours before or after. Many calcium products also contain magnesium or vitamin D, and many antacids contain calcium or magnesium.
For people on weekly Fosamax, the label says to choose the day that best fits their schedule. Calcium can then be taken later in the day, after the wait. Your prescriber or pharmacist can help plan around other morning pills, such as levothyroxine, which has its own empty-stomach and 4-hour rules; see calcium and iron with levothyroxine. Dose Track can set a weekly Fosamax reminder and a later calcium reminder so they do not land together.
Read more on Dose Track: Fosamax side effects · Calcium supplements · Vitamin D3 · Prolia side effects · Reclast side effects