When I first explored Stoicism, I was surprised to learn that they were fine with suicide. In fact, that was one of the few things I learned about them at first. I found out that Zeno of Citium (founder of Stoic philosophy in ancient Athens) broke his toe when he was in his 70s and decided to end his life as a result. It is said that the second head of the Stoic school Cleanthes starved himself to death because he reasoned that he was already halfway down the road of death after having to abstain from eating because of an ulcer. Later, during ancient Rome, Cato the Younger did not believe he could live in a world where Julius Caesar was a tyrant so he disemboweled himself in a protest of Caesar’s reign. So, with all these Stoics killing themselves, does that mean that any type of suicide goes? Well, no.
The Stoics believed that suicide was permissible under a few circumstances. According to Diogenes Laertius (7.130),
[The Stoics] say that the wise man will commit a well-reasoned suicide both on behalf of his country and on behalf of his friends, and if he falls victim to unduly severe pain or mutilation or incurable illness.
Translation from Long and Sedley Vol. I (1987) 425.
So according to Diogenes Laertius, the ancient Stoics believed that the Stoic Sage would sacrifice their life as a duty to protect their friends or their country. The Stoics believed that virtue is the only good and that would sometimes mean jumping in front of a bullet for someone. In the case of Cato the Younger, he felt it was his duty to protest Julius Caesar by suicide. Some believe that Cato’s suicide was pivotal to inspiring Senators to revolt against Caesar and ultimately led to Caesar’s assassination. It is important to realize that to the Stoics, life is merely a preferred indifferent. It is preferable to death, but it is not ethically valuable like virtue is. So sometimes death might be required to do one’s Stoic duty.
The second reason Stoics are permitted to commit suicide is when they have incurable chronic pain, or a terminal illness, and they know that life is going to make it harder for them to carry out virtue. While Stoics did believe that virtue is the only good, they did recognize that dispreferred indifferents (such as misery, disease, a bleak circumstance) could outweigh preferred indifferents (health, wealth, prosperity), so it might be time to call it quits because such circumstances make it difficult to choose indifferents virtuously. If a wise person cannot carry out the necessary steps to assist others and be productive, then the wise person might ask, then what is the point? If you cannot help others, or you know you’ll be in so much pain and be incapacitated two months down the road, you might decide euthanasia is the best course of action.
Diogenes Laertius also lists a third reason for why Stoics might commit suicide,
Avoidance of being forced to do or say immoral or shameful things. The Stoics held that it was permissible, perhaps even the duty, of a person who was being forced to perform an immoral or shameful act to commit suicide to avoid having to do it.
Walter Englert, Seneca and the Stoic View of Suicide (Dec. 1990). The Society for Ancient Greek Philosophy Newsletter.
The Stoics thought that if you live under a tyranny and you have a bully ruler and they try to make you do things that are completely unethical and violate virtue, then it might be necessary to take your life, especially if there is no way to stop the bully. Life is like a game and if you do not agree with the rules, you can just leave the game at any time. Same goes with being forced to speak things you do not believe to be true or go against the truth.
So, the Stoics were only suggesting suicide in situations where you are sober in your thinking, where you have given it some rational deliberation. The Stoics did not by any means ever condone suicide by whim or when one is consumed by pathos (disturbed thinking). So, while the Stoics were quite open-minded about suicide, they weren’t ok with it all situations, especially not in situations where someone is not sober in thinking enough to consider what is the virtuous course of action.
Stoicism | The Four Virtues 