Doctors have a lot of standard medications they use to treat many common physical disorders. For example, when I hit the diabetes border, my doctor prescribed metformin, a reliable (and inexpensive) drug to help control my blood sugar. It has worked admirably and the only side effect disappeared after a few weeks.
It's different with mental illnesses. While there are basically four types of drugs that are used in treating bipolar disorder, within each of those types is a bewildering array of possible medications.
For mood stabilizers and anti-manic drugs, there's lithium, a large group of meds used to treat epilepsy that also help bipolar disorder, and a few others as well.
There's a large number of antipsychotic drugs, and some of them also have mood stabilizing, antidepressant and/or sedative properties.
Anti-anxiety drugs include a class of tranquilizers, and in addition several antidepressants may have a positive effect on anxiety. This type also includes sedatives and many medications that primarily treat other bipolar disorder symptoms but also promote good sleep.
The largest type of drugs used in treating bipolar disorder is the antidepressants. Not only are there dozens of antidepressant medications, but several drugs of other types also have antidepressant properties.
With so many drugs to choose from, a doctor prescribing for a newly diagnosed bipolar patient is likely to choose medications that have worked well in his or her experience. A mood stabilizer is generally the first type of drug chosen.
Particularly in Bipolar I disorder with psychotic features, an antipsychotic may well be the next type of drug prescribed.
My current medications are Lamictal (mood stabilizer), Cymbalta (antidepressant), Seroquel (antipsychotic with antidepressant and sedative properties), and trazodone (mild antidepressant with sedative properties). But since every person's body chemistry is unique, what works for me isn't going to work for everyone.
Trial and error is the rule rather than the exception when a patient is newly diagnosed. Not only does it take time to see how well a medication is working and whether the side effects are a problem, but each time a med is changed, the effectiveness of one or more of the other drugs in the "cocktail" may change, too.
In addition, the efficiency of drugs can change over time. And even minor changes in your physical condition can affect the performance of a medication.
So over your lifetime as a person diagnosed with bipolar disorder, you should expect that one or more of your medications will need to be changed periodically, and there may be another trial and error period while that's being done.
The goal is always stability. Be honest with your doctor when you have a problem with a medication, or when your moods become less stable after you've been taking the same drugs for some time. There are plenty of other meds that can be tried.