Multiple Drug Treatment Effects

#1
Suppose I have five vitamins VA VB VC VD VE, and wish to study the effects of each drug on the weight of patients with data measured at daily frequency.

The typical data look like this Patient 1 take 1000mg of VA at day 15 ; take 1000mg of VD at day 19. Patient 2 take 1000mg of VE at day 35 ; take 1000mg of VB at day 87 ; then take 1000mg of VE at day 99 ....etc

In other words, if I measure the weight of patient 1 at day 25 for example, it includes the consequence of taking both VA at day 15, and taking VD at day 19.

This is the type of data I have, is there any treatment effect methodology that allow me to study the treatment effect of the drugs? So I can make the conclusion like the following : taking a one-time 1000mg VA would decrease weight by 2.9% , 60 days post taking the drug, something like that hypothetically taking a one-time 1000mg VD would increase weight by 1.3%, 60 days post taking the drug.

Thank you