Hello. Regarding your medications: there are no significant interactions reported between alli and tamoxifen or Effexor. And while there is no direct interaction between alli and levothyroxine, as the package labeling states, if you are taking medicaiton for thyroid disease, you shoud talk to your doctor before using alli. Your doctor may want to monitor your thyroid level more closely as you lose weight, as your needs may change with with weight loss.
Your multivitamin should be taken at bedtime - at least 2 hours before or after any alli capsules to maximize absorption of the fat-soluble vitamins A, D, E and K. If you are taking a multivitamin, you can take your calcium supplement as you normally would - it is not affected by alli. Same goes for your glucosaine, B vitamins and vitamin C.
If your vitamin D is in a separate supplement, you can spearate that out and take it at bedtime. If it is combined with the calcium, you can take it as you normally would. While alli may block some of its absorption, the majority of the dose will be absorbed and there is vitamin D in a multivitamin that should provide you with you an adequate amount.
Hope this helps!
Maria Marzella Sulli, Pharm.D.