If your child takes medications such as Ritalin or Adderall to treat attention deficit hyperactivity disorder (ADHD), you should reconsider after two years or so whether the medications are still helping, according to a new CR Best Buy Drugs report. We found that while those drugs help most children and teens with the condition at first, it's unclear how long the benefits last.

We looked at an analysis of more than 400 studies of ADHD medications, including stimulants such as methylphenidate (Ritalin, Concerta, and generics) and amphetamine (Adderall), as well as nonstimulants such as atomoxetine (Straterra), guanfacine (Intuniv), and clonidine (Kapvay). Our findings show that 60 to 80 percent of children with ADHD who take these medications improve their ability to focus, become less impulsive, and are less disruptive at home and school, at least for the first couple of years. But no good quality studies have looked at continued treatment for longer than that.

Several small studies found that the benefits of methylphenidate start to drop off as soon as six months to two years after starting treatment. The largest study, which followed nearly 600 kids ages seven to nine, found that medication combined with close monitoring by a physician was more effective than medication or behavioral therapy alone for at least 14 months. Follow-up with those same kids eight years later showed that nearly 70 percent no longer had ADHD, regardless of what kind of treatment they initially received. (See our ADHD Best Buy Drug report for more details on this study.)

Given these uncertainties, you and your doctor should periodically discuss whether it makes sense for your child to take a break from ADHD medications, even for a short time. Some children might benefit from continuing to take them, while others might "outgrow" their ADHD symptoms and no longer need medication.

When drugs are necessary, our analysis found that stimulant medications reduce ADHD symptoms slightly better than nonstimulant drugs. Among the stimulants, we recommend generic methylphenidate (the generic version of Ritalin), which costs as little as $15 a month, and is as safe and effective as related drugs.

Before starting any ADHD treatment, get a diagnosis from a physician or mental-health professional with expertise in ADHD, and a second opinion if you have doubts. Be skeptical if a doctor or therapist diagnoses ADHD at the first visit and immediately prescribes a drug. A thorough diagnosis usually involves talking to parents and the child's teachers, as well as direct observation of the child in various settings.

Read our latest, free Best Buy Drugs report for more information about ADHD and the effectiveness and safety of medications used to treat the condition.