These include methylphenidate (e.g., Ritalin) and dextroamphetamine, among others. Selegiline may also be useful, as it is "primarily a metabolic precursor of amphetamine and exerts most of its therapeutic effects through amphetamine metabolism."[11] Increased dopamine release is felt to be the main property explaining wake-promotion from these medications.[11] Although stimulants can effectively reduce sleepiness in the short to medium term, they are rarely effective long-term, as patients frequently become resistant to their effects. In addition, there are unpleasant potential side effects, which include heart problems, aggressive behavior, and dependence.[5] Insomnia is another common side effect and may require additional treatment.[29]