The first thing you need to be aware of when taking lithium is that you need to drink plenty of fluids (preferably without sugar or caffeine). If you don't make sure you're flushing your system properly, lithium can build up, possibly leading to toxicity. (See Monitoring Lithium Levels - Why It's Essential.)
It's also important to get enough salt in your diet. Without this, lithium can also build up in your system.
There are a lot of medications that can cause serious problems...