Gemara

3a (Shmuel): Mafis Morsa (piercing an abscess) is permitted.

107b - Version #1 (Mishnah): If one traps [rodents] for a need he is liable. [If it was not for a need, he is exempt.]

(Rav Yehudah): This is like R. Shimon, who exempts Melachah she'Einah Tzerichah l'Gufah.

Version #2 (Mishnah): If one punctures an abscess on Shabbos to make an opening, he is liable. If it was to let out pus, he is exempt.

(Rav Yehudah): This is like R. Shimon, who exempts Melachah she'Einah Tzerichah l'Gufah.

129a: They burned a bench for Rabah [after he let blood, for they could not find other wood].

Abaye: Isn't this Bal Tashchis (being wasteful)?

Rabah: It is preferable not to be wasteful with my health!

135a (Beraisa): A Nefel (stillborn baby) is [Muktzeh] like a stone. One may not move him on Shabbos. However, his mother may bend over to let him nurse [by himself], due to danger [if she is too full of milk].

147a (Mishnah): One may not make Afiktizin [to induce vomiting].

147b (Rabah bar bar Chanah): A potion is forbidden, but one may induce vomiting by hand (stick a finger down the throat).

(Beraisa - R. Nechemyah): It is forbidden even on a weekday, for this wastes food.

Rishonim

Rif and Rosh (63a and 22:16): Presumably, we forbid [inducing vomiting] when there is no pain. If one is in pain, and vomiting cures him, it is permitted. Bahag says so in the name of Rav Tzemach Gaon.

Rambam (Hilchos Shabbos 1:7): One is liable for a Melachah she'Einah Tzerichah l'Gufah.

Rambam (10:17): One may pierce a boil in order to let out the pus inside.

Magid Mishneh: Since the Rambam is Mechayev for Melachah she'Einah Tzerichah l'Gufah, he should be Mechayev for this! It seems that he rules like Version #1 in the Gemara, that even R. Yehudah exempts [and permits]. Shmuel permits, even though he rules like R. Yehudah! Piercing an abscess is a Melachah when he intends to widen the opening. If he just intends to remove pus, it is not a final Melachah.

Rambam (21:31): We do not induce vomiting on Shabbos, i.e. through a potion, lest one grind ingredients. Rather, one may stick his finger into the mouth to vomit.

Rosh (19:5) and Tosfos (135a DH Mipnei): One may nurse a Nefel not only due to danger. It is permitted even due to pain. She may even express her milk, even though it is a Melachah she'Einah Tzerichah l'Gufah, which is more stringent than moving Muktzeh. This is like piercing an abscess. We permit a Melachah she'Einah Tzerichah l'Gufah due to pain.

Tosfos (3a DH ha'Tzad): Bahag asked that here Shmuel exempts Melachah she'Einah Tzerichah l'Gufah like R. Shimon, and permits due to pain. On 42a, Shmuel forbids Melachah she'Einah Tzerichah l'Gufah, like R. Shimon! R. Tam answered that Shmuel taught according to R. Shimon, but Shmuel himself disagrees. However, we hold like R. Shimon, for Rava rules like him, and he is Basra.

Tosfos (107a DH umi'Mai): In Sanhedrin (85a), the Gemara concluded that the Mishnah that permits using a needle to remove a thorn is like R. Shimon. The Ri says that in the Hava Amina, it is even like R. Yehudah. He normally forbids Davar she'Eino Miskaven. Here he permits, due to pain. Likewise, R. Shimon permits piercing an abscess, which is Melachah she'Einah Tzerichah l'Gufah, due to pain.

Poskim

Shulchan Aruch (OC 278:1): One may extinguish a Ner to enable a dangerously sick Choleh to sleep.

Bi'ur Halachah (DH ha'Choleh): In 334:27, we permit extinguishing a wooden coal to avoid damage, for it is Melachah she'Einah Tzerichah l'Gufah. If so, we should permit also for a Choleh without danger! We can say that there we avoid pain of the Rabim, and here we discuss one Choleh.

Shulchan Aruch (328:28): One may pierce an abscess in order to let out the pus inside.

Beis Yosef (DH v'Im): We permit when he wants to remove pus now, and does not care whether or not it closes immediately. Since there is no Tikun, Chachamim did not decree, due to pain.

Magen Avraham (33): This is a Melachah she'Einah Tzerichah l'Gufah. Chachamim did not decree in a case of pain. According to the opinion that obligates for Melachah she'Einah Tzerichah l'Gufah, piercing to remove the pus is not the final Melachah. He can never come to a Chiyuv for Makeh b'Patish. Alternatively, this is Davar she'Eino Miskaven.

Mishnah Berurah (88): One may remove a splinter with a needle, as long as he is careful not to draw blood, for this is a wound (Sanhedrin 84b). Even though this is Mekalkel (destructive), all forbid. Even though they permitted an Isur mid'Rabanan regarding abscesses due to pain, here, since one can remove the thorn without drawing blood, one should not transgress without need.

Kaf ha'Chayim (167): One should puncture it only with a needlepoint, but not with his fingernail, lest he tear off skin, which is Gozez. However, Tosfos (brought in the Magen Avraham - PF) at the beginning of Siman 340 holds that Gozez is a Melachah she'Einah Tzerichah l'Gufah. If so, if it is impossible in any other way, one may tear off a little skin, to avoid pain. However, the Rivash forbids according to everyone.

Kaf ha'Chayim (169): Even if he is healthy, one may open it to remove the pus, due to pain.

Shulchan Aruch (31): If a fingernail detached and thin strands of skin around the nail, if the majority separated l'Ma'alah (above) and they are paining him, he may remove them by hand.

Mishnah Berurah (96): Since the majority detached, they are close to coming off and it is as if they are detached, so Chachamim were not stringent in a situation of pain, if one removes them through a Shinuy. One must be careful not to draw blood.

Shulchan Aruch (ibid.): Rashi explains that 'l'Ma'alah' means towards the fingertips. R. Tam explains that it means towards the body. One must be concerned for both opinions.

Shulchan Aruch (35): A woman may make her milk flow so a baby will nurse.

Kaf ha'Chayim (205): All needs of a child are like a Choleh without danger.

Mishnah Berurah (112): She makes it flow into the baby's mouth.

Sha'ar ha'Tziyun (81): Tosefes Shabbos (59) says that this is Melachah she'Tzerichah l'Gufah. Why is it permitted? He says that expressing human milk even into a Kli is Mefarek k'Le'acher Yad (unskillfully), for it is normal only to nurse from people, unlike the Levush. This is wrong. See Tosfos 135a. (He exempts due to Melachah she'Einah Tzerichah l'Gufah.) The Pri Megadim says that the Shulchan Aruch discusses expressing onto the ground, and the baby sees [and nurses]. However, Shibolei ha'Leket permits expressing into the baby's mouth. Perhaps this is because it is dangerous if the baby will not nurse. This requires investigation.

Kaf ha'Chayim (206): If needed, she may make it flow into his mouth.

Rema: She may not spray her milk on someone seized by a Ru'ach Ra'ah without danger.

Beis Yosef (DH Kasav): R. Binyamin says that there is not even excessive pain [due to the Ru'ach Ra'ah].

Magen Avraham (41): If there were excessive pain, it would be permitted, for it is a Melachah she'Einah Tzerichah l'Gufah. See Sa'if 17 and 278:1.

Eshel Avraham: Why in Sa'if 17 do we forbid for a Choleh without danger? (One opinion forbids anything close to a Torah Isur, even if there is danger to a limb!) Why are we more lenient for piercing an abscess and similar matters? The Rambam holds that piercing an abscess is not even Melachah she'Einah Tzerichah l'Gufah.

Kaf ha'Chayim (209): If one has a great ear ache, a wet nurse may spill a drop straight into his ear, since it is Melachah she'Einah Tzerichah l'Gufah. The same applies to one with a great headache.

Shulchan Aruch (39): One may not make Afiktizin even during the week, due to wasting food. If one is in great pain due to overeating, it is permitted during the week, and on Shabbos it is forbidden through a potion and permitted by hand.

Beis Yosef (DH Ein): Rashi explains that Afiktizin is not for Refu'ah, rather, to empty the intestines to enable him to eat more. The Rif and Rosh permit when there is pain. I.e. it is not forbidden due to wasting food, but one may not use a potion on Shabbos, since it is possible by hand.

Gra: We learn from 129a.

Damesek Eliezer: There we find that Bal Tashchis does not apply if it alleviates pain.

Note: Seemingly, the cold was hazardous to Rabah's health!

Kaf ha'Chayim (229): If one cannot vomit by hand, or it is very painful for him, he may drink hot water to induce vomiting. It must be hot from before Shabbos. If he is in great pain, they may ask a Nochri to heat it.

Shulchan Aruch (330:8): One may not move a Nefel on Shabbos. However, his mother may bend over to nurse him if her milk is paining her. She herself may express her milk if it is paining her.

Beis Yosef (DH v'Chasav): The Mordechai (371) says that R. Nisim Ga'on learns from the Tosefta (10:14) that a woman may not express milk. However, some (Or Zaru'a) say that this is only into a Kli, for this is Mefarek, a Toladah of Dash. She may express onto the ground.

Magen Avraham (17) and Gra: This is like piercing an abscess.

Mishnah Berurah (32): She may express onto the ground. This is unlike Mefarek, for the milk is wasted. Also, it is Melachah she'Einah Tzerichah l'Gufah. Chachamim did not decree due to pain, just like piercing an abscess.

Shulchan Aruch (340:2): One may not cut a wart from his body, with his hand or a Kli, whether for himself or for another.

Bi'ur Halachah (DH Yabeles): If something is normally detached by hand, one is liable due to Gozez. If so, even if the majority separated, those who permit in 328:31 to detach (thin strands around the nail) when they pain him, here it is forbidden. Since it is normal with the hand, this is like with a Kli.