If you have, say, 4 prescriptions that are all “take 3 times a day” you can often take the 4 medications at once, which is handy.

But some say “take on an empty stomach” and some say “take with food or milk”. If 2 of the 4 have those labels, they can’t be taken together. You need to take the first about half an hour before a meal. The other 2 may say nothing about food or say they can be taken with or without food. As long as nothing I bring up later comes up, you can take the others before breakfast or with it.

Maybe you take calcium in the form of Tums because you can swallow it, unlike the horse pill. A few pills say not to take with antacids. So watching when you take vitamins, especially chewable ones (horse pill calcium still slowly acts as an antacid, but the slower dissolving makes it not so much a factor).

Taking your sleeping pills in the morning (assuming you don’t work graveyard shift) would not make sense. Taking a medication meant to keep you alert, whether an ADHD drug or one for narcolepsy, with it is worse.

(I know that ADHD is more than lack of focus but when I am overfocused I am not alert to hunger, thirst, and can’t shift attention to the person asking me to do x long enough to remember that maybe I saw them but don’t know why).

Some antidepressants make you sleepy in their initial hours of working, others wake you up a bit during the same time. So advice to use one in the morning or the other at bedtime are for a reason.

There are problems with polypharmacy. This means the number of meds taken even if they are taken at different intervals on the same day as well as at the same time.

With each drug comes risks and contraindications, those that have additive effects and those who reduce the effectiveness of others. Some decrease adsorption of others for example calcium and magnesium. There are meds that need to be taken with meals and those that should be taken on an empty stomach. Some foods or beverages interfere with the metabolism of other drugs such as grapefruit juice.

Complicated instructions for each drug make compliance more difficult.

Sometimes conditions are complicated so there may need to be multiple approaches to controlling a condition and there is more information learned about pathophysiology every day. Multiple meds may be tried in an attempt to decrease side effects known to appear when higher doses of one agent are used. However, this still increases the chance that there will be interactions.

Your highest risk is Drug-Drug interactions that may result in adverse drug reactions (ADR). Preventable Adverse Drug Reactions: A Focus on Drug Interactions

According to the FDA ADRs cause 100,000 deaths annually. They result from drugs interacting in the body at two levels

  1. one drug may interfere with another drug’s mechanism of action (pharmacodynamic interactions)
  2. one drug may prevent or increase the metabolism (breakdown) and excretion (removal) of another drug (pharmacokinetic interactions) from the body thus
    1. diminishes drug levels due to faster removal or
    2. increases levels way above normal due to decreased removal.
  3. another possibility is the incidence of genetic mutations that alter ones ability to metabolize (breakdown) a drug

There are laboratory tests available that your doctor can request to help mitigate this consequences as well as identify possible drug drug interactions (DDI).

It all depends on what kind of drugs you take together.

You have to do internet researches to make sure the drugs you take together are not dangerous when taken together…

You could ask a Doctor but since there are thousands of drugs I don’t think they can know for sure. Unless they have a special tool reserved for them. It’s also the job of pharmacists, at least in France, to make sure that the Doctor’s prescriptions make sense.

Also, there are families of drugs, such as Benzodiazepines and Opioids. Taking both in high dosages can be very fatal.