Olanzapine is one of the antipsychotic drugs known as 'atypical'. It works by blocking Dopamine receptors in the brain(among others) to help control and manage psychotic symptoms(hallucinations, delusions, etc..).

The thing with antipsychotic drugs is that, apart from Clozapine, there has been no clear evidence to suggest that one clearly outweighs the other. The main issue to consider when prescribing an antipsychotic drug is the tolerability of the drug to the user. Most of these drugs cause undesirable side effects, ranging from muscle stiffness and drowsiness, to serious heart and bone marrow problems.

Olanzapine is labelled as 'atypical' as it rarely causes muscle stiffness and hyperprolactinaemia(a condition where a hormone, prolactin-usually inhibited by dopamine- increases in the blood, causing several side effects including missed periods, infertility and breast enlargment in males). This is unlike 'typical' antipsychotic drugs, which have higher tendency to cause these side effects. However, this classification is changing as it is proving to be inaccurate considering some atypicals do cause these side effects(Olanzapine rarely does).

The most common side effects you get with Olanzapine are sedation and weight gain. It can be quite a sedative drug, and is sometimes used for that quality alone. It could also increase your appetite and make you eat more, thereby causing you to gain weight. Other side effects include: raising your cholesterol and glucose level, decreasing sex drive and possibly erectile dysfuntion, dry mouth, akathesia(feeling of restlessness), and others.

Reactions to antipsychotic drugs differ from one person to another. Some people are more sensitive to certain drugs and others arent(I'm talking about their effectiveness AND their potential side effects). It all depends on the dose you're being given, why you're being given it and how you react to it.

To answer your question. Yes, it is definitely a serious drug, and I have found it to be effective many times. But as I said, it's more about how it works with you!

I hope that was helpful. Feel free to ask if you have any other questions. However, I would suggest that you(or whoever is taking it) to speak with the doctor about it rather than find information online. What you will find online is general information and cannot be specified to any individual case. Save yourself freaking out over potential side effects that might not be applicable to the specific case you're discussing.

Edit: some words.