Maimonides was a highly regarded medieval physician and Sephardic Jewish philosopher. He was an influential Torah scholar. He was also referred to by the acronym Rambam. Maimonides was born in present-day Spain in 1135 or 1138. He worked as a rabbi, physician, and philosopher in Morocco and Egypt, where he died in 1204. This is from the Mishneh Torah, his review of the Torah. It is a legal digest that encompasses the entire range of Talmudic literature. Scholars widely regarded the Mishneh Torah as Maimonides’ magnum opus, and an extremely influential work.

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Mishna Torah (English translation)

Excerpts

19. Semen is the strength of the body, its life [force], and the light of the eyes; the greater the emission [of sperm], [the greater] the damage to the body, to its strength and the greater the loss to one’s life [span]. This was implied by Solomon in his wisdom: “Do not give your strength to women” (Proverbs 31:3).

Whoever is steeped in sexual relations, old age springs upon him [before its time], his strength is depleted, his eyes become dim, a foul odor emanates from his mouth and his armpits, the hair of his head, his eyebrows, and eyelashes fall out, the hair of his beard, armpits and legs grows in abundance, his teeth fall out and he suffers many pains beyond these. The wise of the doctors have said: One of a thousand dies from other illnesses and a thousand from excessive intercourse.

Therefore, a person must take care in this matter if he wishes to live in good [health]. He should not engage in intercourse except when the body is healthy and particularly strong.

Note: No clear recommendation of Synergy itself has yet turned up in the Jewish tradition, but as a practice Synergy is very likely permissible under the rubric of medical/psychological interventions for Jews, given that there are experts who believe it works. According to a rabbi, this rule holds even when knowledge comes from a source that is contrary to the faith.