Tricyclics and monoamine oxidase inhibitors (MAO inhibitors or MAOIs) are older classes of medications that work differently from the antidepressants used to treat bipolar disorder and even differently from one another. These meds are used much less often than many of the other treatments for bipolar because the side effects of tricyclics and MAOIs can be difficult to manage:
Tricyclics: Tricyclics affect norepinephrine and serotonin levels primarily, but they also touch a number of other brain chemicals, including histamine. These "extra" chemical events cause many side effects, which may include sedation, dry mouth, constipation, and dizziness, as well as cardiac rhythm changes.
Monoamine oxidase inhibitors: MAOIs prevent the action of an enzyme that breaks down norepinephrine, serotonin, dopamine, and a number of related brain chemicals, which increases the levels of these chemicals in the brain. People taking MAOIs are restricted from eating certain foods, including but not limited to aged meats and cheeses and certain types of beans, to prevent a dangerous spike in blood pressure.
MAOIs can also have severe interactions with many other meds and, in particular, are very dangerous with SSRIs and SNRIs. If you're changing to or from MAOIs to an SSRI or SNRI, you must have a complete two-week washout of one medication before starting the other. When changing from fluoxetine to an MAOI, the washout period between medicines should be five weeks.