One of my patients I saw last week developed osteoporosis while taking Topamax (topiramate). Topiramate is known to cause osteoporosis by causing loss of calcium through the kidneys. While osteoporosis is not common, we don’t know if it is really that rare. A side effect that was thought to be rare (less than 1%, according to the manufacturer) when the drug was launched, is kidney stones. Now we know that close to 20% of people taking topiramate for a long time, develop kidney stones. Both kidney stones and osteoporosis occur through similar mechanisms, so it is possible that osteoporosis is also much more common than doctors think.
This patient had no other side effects and topiramate was very effective in controlling her migraines. Since osteoporosis is a very serious and potentially dangerous condition, she will have to stop taking topiramate. However, she does have other options because she has never tried Botox injections and several other drugs for the prevention of migraines.
Another very serious side effect that is not obvious to women taking Topamax, is the potential for serious problems in the fetus. The FDA designates topiramate as belonging to category D: “Pregnancy Category D drugs are those with positive evidence of human fetal risk based on human data, but still may be used in pregnant women in certain situations when its benefits are thought to outweigh potential risks”. Drugs in category B are considered to be safe in pregnancy, while category C means that there is not enough data and category X means it is absolutely contraindicated in pregnancy.
Topamax (topiramate) is one of the more popular drugs for the prevention of migraines (as well as treatment of epilepsy). It works only in half of the patients, while for the other half it doesn’t work or causes unacceptable side effects. The reason for its popularity is that unlike many other medications which can cause weight gain, this one often causes weight loss.
In addition to the side effects that occur over time, there are many that happen quickly and which are usually, but not always, patients easily linked to the drug: 1) cognitive impairment, such as inability to recall a word, slow thinking, or as some patients tell me, feeling stupid, 2) drowsiness, 3) dizziness, 4) fatigue, 5) blurred vision due to an acute glaucoma, and other.
