When to expect results from a new medication

Each one can have a different timetable. Find out in advance what you should expect, and then track your symptoms.

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When your doctor prescribes a new medication, you may expect to start feeling the effects right away. But some drugs can take time to make a difference. "It depends on how quickly your body absorbs the medication, how your body distributes it, and how your body breaks down or metabolizes it," says Laura Carr, a pharmacist at Harvard-affiliated Massachusetts General Hospital.

Giving it time

Some medications start working on the first day. These include drugs that treat high blood pressure, like the beta blocker metoprolol (Toprol, Lopressor), which slows down the heart and reduces the force of its contractions; or H2 blockers such as famotidine (Pepcid) and ranitidine (Zantac), which treat heartburn by blocking the stomach's acid-secreting cells from making acid.

Some medicines can take longer to start working. For example, it might be two to four weeks before a cholesterol-lowering statin drug like atorvastatin (Lipitor) takes effect. It blocks an enzyme that the liver needs to make cholesterol. With less cholesterol circulating in the blood, the body is forced to better use and break down the remaining cholesterol. But it takes time for that effect to kick in.

And it may be months before you feel the full effects of certain drugs, such as medications to treat depression — like sertraline (Zoloft). "The antidepressants that have been available so far work to enhance the activity of chemical messengers between nerve cells. That direct effect is immediate, but mood improvement seems to depend on a downstream effect on brain circuits that modulate mood. Those changes take longer to develop," says Dr. Michael Craig Miller, an assistant professor of psychiatry at Harvard Medical School.

"As a pharmacist, I always tell patients starting on new antidepressants to be sure to wait a full 12 weeks before deciding if it is helping with their symptoms," says Carr.

Monitoring progress

You may be able to monitor your own symptoms to see if a drug makes you feel better. "That can be the case for medications that lower blood pressure or blood sugar, or treat depression," Carr says. It's helpful to track when you've taken a medication and any changes in symptoms you experience.

Sometimes your doctor will want to monitor a medication's effectiveness with blood tests. That may be the case if you're taking a statin. Your blood cholesterol level will be checked periodically, to be sure the drug and dose are achieving the desired effect.

If you start a new medication and you feel you are having new symptoms or your symptoms are getting worse, then you should contact your doctor right away.

When a medication doesn't seem to be working

If you're concerned that a new medication is not working, you should always talk with your doctor or pharmacist.

But whatever you do, don't stop taking the drug without speaking to your doctor first. "Some medicines need to be stopped slowly, over time, to prevent side effects or worsened symptoms," Carr says. For example, suddenly stopping an antidepressant or a medication to treat heartburn may actually provoke symptoms.

A better plan: talk to your doctor about finding a more effective drug. "For common conditions, such as high blood pressure, high cholesterol, diabetes, or depression, there are many different medicines that your doctor can use to treat your condition," Carr says. "Just keep in mind that it can take time to find the one that's right for you."