Consider the following scenario: A patient has advanced metastatic cancer and the doctors believe she will succumb to the illness. “There is one new experimental treatment which may possibly reverse the disease,” she is told, “but the treatment is dangerous, and if it does not succeed it will kill you.”

The patient must now decide: Should she undergo the risky experimental treatment or let the disease take its course? On the one hand, the intervention may deprive her of the remaining short time she has to live, but on the other hand, it offers a chance for a cure. What would Jewish law (halachah) say in this situation? Would one be allowed to undergo this risky treatment?

Defining Terminal Illness - “Chayei Shaah

We first need to establish what exactly we mean when we say “she does not have long to live.” In halachah, this is a state known as chayei shaah, or “temporary life,” in contrast to its counterpart, chayei olam, “indefinite life” (meaning, not terminally ill).

The exact definition of chayei shaah is debated among Jewish scholars, with opinions ranging from a life expectancy of six to 12 months,1 to as few as seven or even three days.2 Others focus less on an exact length of time, maintaining that chayei shaah means anyone with a terminal illness to which they will ultimately succumb.3

(There is a related term in halachic literature known as gosses,”4 someone whose death is imminent,5 which is beyond the scope of this article. Some scholars, however, believe that a gosses and one with only chayei shaah remaining are one and the same. Others advocate the more expanded definition of chayei shaah outlined above, maintaining that a gosses implies a far more dire condition.)

Halachic Attitude Towards Chayei Shaah

Regardless of the exact timeframe, the implication of chayei shaah is that life expectancy is limited. Halachah places immense value on human life, and one with chayei shaah remaining is no different. For example, if a building collapses and we suspect a person is trapped underneath, we may do whatever is needed to rescue that person on Shabbat when such activity would normally be forbidden. Even if we discover, while excavating, that the trapped person is mortally wounded and has only chayei shaah remaining, we continue our efforts to free the person.6

Similarly, when discussing a gosses, halachah urges us to be extremely careful to avoid anything that might shorten his life; any such action would constitute murder.7

Let’s return to our patient scenario with the assumption that the prognosis fits the definition of chayei shaah. Given the extreme value that halachah places on life, including one who has only chayei shaah remaining, would the patient be allowed to undergo treatment (potential for cure notwithstanding) that may jeopardize her chayei shaah?

Risking Chayei Shaah

The Talmud addresses a comparable scenario, and discusses whether a Jew may seek help from a doctor who is a virulent anti-Semite, suspected of inflicting harm on his Jewish patients.8 The consensus is that while generally one would be forbidden from visiting such a practitioner, a person who is already terminally ill and in a state of chayei shaah may do so despite the risk to his life, for the small chance that he may in fact be cured.

In issuing this ruling, the Talmud draws precedent from the story of the four lepers.9 During the war with the Arameans, there was a famine in the besieged Jewish encampment. Four lepers, banished to the outer gates, were likewise starving, and decided to surrender themselves to the nearby Aramean encampment:

“If we say that we will come into the city, with the famine in the city, we will die there, and if we stay here we will die. So now, let us go and let us defect to the Aramean camp. If they spare us we will live, and if they kill us we will die.”10

The Talmud considers these men, in their dire state of starvation, to be in a state of chayei shaah.11 By defecting to the Aramean camp, they risked being killed immediately, but there was also a chance they would be kept as prisoners and fed, thereby saving themselves from inevitable starvation. Based on this anecdote, the Talmud concludes that one may jeopardize chayei shaah for the chance to achieve chayei olam.12

As a result of this Talmudic ruling, many halachic experts agree that a person may undergo treatment for the chance to achieve a cure, even if it may jeopardize their remaining chayei shaah.13

Defining “Risky Treatment”

There are still several factors that must be addressed. For instance, does it matter how risky the treatment is? In our scenario above, if the treatment has a 95% chance of death, would the patient really be allowed to assume that risk? And if the treatment has only minimal risk, then perhaps she should not only be allowed to assume that risk, but be obligated to, under the general mandate to guard and optimize one’s life!14

Rabbi Moshe Feinstein, one of the foremost halachic experts of post-war Jewry, published extensive responsa addressing this issue,15 concluding that if the chance for success is greater than 50%, the patient is not only allowed to undergo the treatment, but is halachically obligated to do so. If the chance of success versus risk is an even toss up with a 50% chance of death, then it is allowed, but not required.16

When it comes to treatments that are associated with a relatively high degree of risk, Rabbi Feinstein notes that although there is some debate in the halachic literature (with one prominent authority forbidding it17 and another permitting it18), if the patient wanted to do the risky treatment, he or she could rely on the more lenient position and undergo the treatment despite the high degree of risk.19 This position, which allows one to undertake the treatment even if the risk of death is greater than 50%, has been qualified by some20 as only being allowed if that risk does not exceed 70%.21

Even when the risk is considered low, and one would be allowed or even obligated to undergo this treatment, it goes without saying that there has to be a reasonable chance of success.22 According to several halachic experts, there has to be at least a supermajority consensus of two-thirds of the physicians in the field that there is a chance of success with this treatment.23

Additional Mitigating Factors

The operative factor here is that the risky treatment must have the potential to convert a patient from the status of chayei shaah to that of chayei olam. If, however, the patient is not in a chayei shaah status, this allowance to undergo risky treatment may not apply. For example, if the patient does not have a terminal illness but is severely incapacitated, and the risky treatment can alleviate the suffering, many halachic experts opine that the patient would not be permitted to endanger himself for this quality of life factor.24 (There is an opinion, however, that if in this setting the patient requests the risky treatment, then it may be nonetheless permitted.25)

Conversely, if the patient is indeed in chayei shaah status, but it’s questionable whether the risky treatment will directly address the cause of that status, then it would not be permitted. For example, a scenario was presented to Rabbi Yitzchok Zilberstein concerning a patient who was severely malnourished and cachectic from a combination of underlying comorbidities. The patient, already in a tenuous state, then contracted bronchitis, placing him in grave danger. The bronchitis could be treated with antibiotics, but the antibiotics could also cause serious side effects. Rabbi Zilberstein was inclined to permit the antibiotics, despite the potential for harm, based on our discussion above. His father-in-law, halachic expert Rabbi Yosef Shalom Elyashiv, overruled him, however, stating that our discussion of chayei shaah would not apply in this case, because the patient’s deteriorating health was not exclusively due to bronchitis, and treating the bronchitis would not reverse the underlying deterioration of health.26


If a patient has a terminal illness, then in certain situations he or she may undergo treatment that has the potential to reverse the terminal illness despite the risk associated with the procedure. Of course, as with any topic in the field of medical ethics and halachah, for practical guidance a rabbinic authority competent in both fields should be consulted.

May G‑d Almighty grant strength to all those facing these challenging situations, remembering His promise to the nascent Jewish nation on the eve of battle: “Be strong and resolute; do not be terrified or dismayed, for the L‑rd your G‑d is with you wherever you go.”27