It depends, says Noah Rosen, MD, assistant neurology professor at Great Neck, NY’s Cushing Neuroscience Institute and director of the Headache Center there, on factors including migraine type, how long you’ve had migraines, and how often they strike. Brace yourself. Pinpointing the right medication for you may be frustrating, because trying out a new migraine drug to see if it works takes time.

When starting a preventive migraine medication, such as topiramate (Topamax), determining how effectively it eases migraine severity and/or frequency can take four to six weeks. Physiological changes that such medications can cause (including difficulty concentrating) can also take weeks to emerge.

If the drug works for you and you continue, allow three to six months to see its full effectiveness as it further improves the headaches. (If it didn’t work for you, you might consider, at this point, changing to a different medication, which, when started would require the same four-to-six-week trial.)

Generally, when you start any preventive treatment—whether a prescription drug, acupuncture, or biofeedback—expect to be on it for three to six months. Within that range, you and your doctor can reassess your condition, determining treatment success and whether stopping is possible. In research studies, successful treatment is defined as having reduced headache frequency by at least 50 percent.

To assess success, our practice monitors headache frequency over the past one to three months, gauges whether the pain index (or episode severity) decreased, and/or reviews whether any existing disabilities (including lost work time) improved. No specific numbers advise us when to stop treatment, so decisions are tailored to individuals.

If, after you stop a medication, headaches later return or worsen, you may start the same medication a second time (if it was successful the first time, but the dose was too low, or the duration too short, for the benefits to last). Expect to be on it for six months to one year this second time, giving the drug more time to further suppress the condition.

If still later you start the same medication a third time, because prior treatments’ effects faded, you’ll likely take it for an extended time, possibly for life. At this point, you might also consider a different treatment.

Remember, each time you stop a migraine medication, to work closely with your doctor to taper down doses gradually to avoid any unpleasant withdrawal effects.