Key takeaways

Healthcare providers consider height and weight, as these can affect the dosage and effectiveness of medication, with a “one size fits all” approach generally applied for adults.
The patient’s sex and age are crucial factors, as men and women metabolize drugs differently, and children and older adults have unique prescription needs due to their physiological differences.
Existing medical conditions and the potential for drug interactions are thoroughly evaluated to ensure that the prescribed medication will not adversely affect the patient’s health.
Communication between the patient and healthcare provider is emphasized as key to managing medication effectively, including discussions about medication intolerance or allergies.

In the United States, 66% of adults take at least one prescription medication. Yet, the average person is likely oblivious to the details that a healthcare provider uses to determine the appropriate prescription and dosage. It’s a process that involves choosing the right medication for your condition, the best timing and amount for your body, all while taking into account any other treatments or underlying conditions that could lead to side effects. In other words, medication prescribing is complicated.

The 6 main variables of medication prescribing

To make sure the treatment and dosage is safe for you, your healthcare provider will consider the prescribing info of the drug found in the package insert in addition to the following factors before sending a prescription to your pharmacy.

1. Height and weight

If you were to compare a smaller-framed person to a tall and broad person and discovered that they both took the same dose of the same prescription, you’d probably be pretty confused. Doesn’t your size make a difference when it comes to the dosage of a medication you take?

The answer is complex, but for most common pharmaceuticals, a “one size fits all” approach actually works out just fine for adults (the dosages of many medications for children are based on weight). When drugs are approved by the FDA for public use, they are assigned a therapeutic index. This means that the effectiveness of the medication is weighed against the potential side effects, and a proper dosage is then established.

Many drugs have a high therapeutic index to account for variations in height and weight, so most adults are able to take a generalized dose without experiencing negative effects. Some medications naturally have a lower (also called narrow) therapeutic index and in these instances, more care is exercised by prescribing physicians. Monitoring may be required, for example, with a blood thinner like Coumadin (warfarin).

2. Sex

Men and women metabolize certain drugs differently. For example, the recommended dose of the popular sleeping pill, Ambien, is about half for women as it is for men. There are several reasons, but primarily the speed of absorption in the gastrointestinal tract and processing by the kidneys varies between the sexes. That impacts how long it takes for medication to be absorbed by the body, and cleared from the body, creating different time intervals for the next dose.

3. Age

While a patient’s body size may not play a huge part in issuing prescriptions, that rule only applies to adults. Children are in a category all their own and their smaller bodies react differently to certain medications. Although these younger individuals will need specific consideration at the doctor’s office, another group does as well.

Ideally, it’s every doctor’s goal to issue a prescription to a patient and have their symptoms dissipate without them incurring too many side effects. However as we age, our risk of negative reactions increases—putting older adults in their own category as well. While part of the issue comes with the natural tendency of older individuals to have multiple medical needs and thus multiple medications, normal aging also plays a role.

An increase in body fat and a decrease in memory, kidney, and liver function, body fluids, and digestive system functions all affect how well one’s body can handle a specific prescription. Those who are older need to ensure they have clear communication with their physician about all the medications and supplements they are taking.

4. Existing medical conditions

There are some instances where a patient’s current medical condition(s) will affect the prescription that a doctor will recommend. Some groups are a little more obvious, like pregnant women, and extra care must be used when determining if medication is appropriate for their specific circumstances.

One such concern is in patients with liver disease, specifically when jaundice or encephalopathy is also present. Because the liver plays such a large role in our ability to metabolize pharmaceuticals and eliminate them from our system, doctors have to be careful.

If you have liver complications and are concerned about how your medications might affect you, discuss these matters with your physician.

5. Drug interactions

Yet other individuals with chronic conditions have to be very careful when it comes to drug interactions, and your doctor should be well aware of the potential complications. Whenever you get a new prescription, it merits a conversation with your physician and pharmacist about all the other medications and supplements you are taking—including over-the-counter treatments. There are many seemingly harmless drugs that can have dangerous interactions with certain medications.

6. Medication intolerance

Some individuals find that they are especially sensitive to the effects of certain medications as well. Termed “drug intolerance” by the medical community, it can make the task of prescribing drugs very challenging for physicians. Aside from this intolerance, some people exhibit an actual drug allergy in which their immune system plays a large role.

Communication is key

Whether you’re currently on prescription drugs or you’ll be visiting your physician soon, it’s important to remember that you have a say when it comes to the pharmaceuticals that are recommended for you. Clear communication and appropriate expectations are crucial for you to maintain your health.

Varying options are available based upon your needs including adjusting doses, switching to or from generic medications, or finding alternative therapies. Always discuss any issues with your healthcare provider—never try to adjust or change a medication on your own.